iTRAQ-Based Proteomics Investigation of Critical Response Proteins in Embryo and Coleoptile During Rice Anaerobic Germination

Direct-seeding of rice has become popular in recent years due to its low cost and convenience,however,hypoxic condition limits seedling establishment.In this study,weedy rice WR04-6 with high germination ability under anaerobic conditions was used as a gene donor,and we successfully improved the seedling establishment rate of rice cultivar Qishanzhan(QSZ)based on selection of a new rice line R42 from the recombinant inbred line population.R42 inherited high anaerobic germination(AG)ability,and was used for isobaric tags for relative and absolute quantitation(iTRAQ)-based comparative proteomic studies with QSZ to further explore the molecular mechanism of AG.A total of 719 differentially abundant proteins(DAPs)were shared by R42 and QSZ responded to AG,and thus defined as common response DAPs.A total of 300 DAPs that responded to AG were only identified from R42,which were defined as tolerance-specific DAPs.The common response and tolerance-specific DAPs had similar biochemical reaction processes and metabolic pathways in response to anoxic stress,however,they involved different proteins.The tolerance-specific DAPs were involved in amino acid metabolism,starch and sucrose metabolism,tricarboxylic acid cycle pathway,ethylene synthesis pathway,cell wall-associated proteins and activity of active oxygen scavenging enzyme.The in silico protein-protein interactions for the top 60 DAPs indicated that tolerance-specific DAPs had relatively independent protein interaction networks in response to an anoxic environment compared with common response DAPs.The results of physiological indicators showed thatα-amylase and superoxide dismutase activities of R42 were significantly increased under anoxic conditions compared with aerobic conditions.Multiple lines of evidence from western blot,physiological analysis and quantitatDirect seeding of rice has become popular in recent years due to its low cost and convenience,however,hypoxic conditions can limit seedling establishment.In the present study,weedy rice WR04-6 with high germination ability in anaerobic conditions was used as the gene donor and successfully improved the seedling establishment rate of rice cultivar Qishanzhan(QSZ)based on selection of a new rice line R42 from the recombinant inbred line(RIL)population.R42 inherited the had high anaerobic germination(AG)ability,which was used for the isobaric tags for relative and absolute quantitation(iTRAQ)based comparative proteomic studies with QSZ to further explore the molecular mechanism of AG.A total of 719 differentially abundant proteins(DAPs)shared by R42 and QSZ responded to AG and were thus defined as common response DAPs.A total of 300 DAPs that responded to AG were only identified from R42,which were defined as tolerance-specific DAPs.The common response and tolerance-specific DAPs had similar biochemical reaction processes and metabolic pathways in response to anoxic stress,however they involved different proteins.The 300 tolerance-specific DAPs were involved in amino acid metabolism,starch and sucrose metabolism,TCA cycle pathways,ethylene synthesis pathway,cell wall-associated proteins and activity of active oxygen scavenging enzyme.The in silico protein-protein interactions for the top 60 DAPs indicated that tolerance-specific DAPs had relatively independent protein interaction networks in response to an anoxic environment compared with common response DAPs.The results of physiological indicators showed thatα-amylase and SOD activities of R42 were significantly increased under anoxic conditions compared with aerobic conditions.Multiple lines of evidence from western blot,physiological analyses and real-time PCR jointly supported the reliability of proteomics data.In summary,our findings deepened the understanding of the molecular mechanism for the rice response to AG.ive real-time PCR jointly supported the reliability of proteomics data.In summary,our findings deepened the understanding of the molecular mechanism for the rice response to AG.

Genetic Characterization of Genetic Resources of <i>Aegilops tauschii</i>, Wheat D Genome Donor, Newly Collected in North Caucasia

For the purpose of broadening the available genetic resources to improve wheat breeding and to elucidate wheat evolution, 16 accessions of Aegilops tauschii newly collected in North Caucasia named NCT accessions were characterized genetically based on morphology, chloroplast SSR variation and AFLP. Ae. tauschii is one of the most important wild wheat genetic resources because it is the progenitor of the D genome of hexaploid wheat. Since Caucasia is considered to be a center of diversity of both cultivated and wild wheat, a lot of studies have been conducted to evaluate the diversity of Caucasian genetic resources including Ae. tauschii. Such kind of analyses, however, focused on Transcaucasia but little attention has been paid to North Caucasia because of the lack of available genetic resources. Based on the molecular analyses in this study, the 16 NCT accessions were generally divided into two groups although morphologically those are classified into the same subspecies. The grouping also represented geographical distribution, that is, the northern part group and Derbent group. This division is consistent with the two major genepools in Ae. tauschii reported in previous studies. The northern part and Derbent groups correspond to Eurasian wide genepool (called Tauschii genepool) and Caucasia and Caspian coast limited genepool (Strangulata genepool), respectively. Regarding to chloroplast, all the 16 accessions were genotyped as HG7, the most major haplogroup of the species. Although all the 16 NCT accessions were categorized into ssp. tauschii morphologically, accessions of Derbent group showed a tendency to have larger spikelets. Among them, especially NCT3 had the quite large size of spikelets and grains that are at almost the largest level in ssp. tauschii. The results of this study filled the missing information of Ae. tauschii and will be helpful for future utilization.

Coat protein of Chinese wheat mosaic virus upregulates and interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase,a negative regulator of plant autophagy,to promote virus infection

Autophagy is an intracellular degradation mechanism involved in antiviral defense,but the strategies employed by plant viruses to counteract autophagy-related defense remain unknown for the majority of the viruses.Herein,we describe how the Chinese wheat mosaic virus(CWMV,genus Furovirus)interferes with autophagy and enhances its infection in Nicotiana benthamiana.Yeast two-hybrid screening and in vivo/in vitro assays revealed that the 19 k Da coat protein(CP19 K)of CWMV interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenases(GAPCs),negative regulators of autophagy,which bind autophagy-related protein 3(ATG3),a key factor in autophagy.CP19 K also directly interacts with ATG3,possibly leading to the formation of a CP19 K–GAPC–ATG3 complex.CP19 K–GAPC interaction appeared to intensify CP19 K–ATG3 binding.Moreover,CP19 K expression upregulated GAPC gene transcripts and reduced autophagic activities.Accordingly,the silencing of GAPC genes in transgenic N.benthamiana reduced CWMV accumulation,whereas CP19 K overexpression enhanced it.Overall,our results suggest that CWMV CP19 K interferes with autophagy through the promotion and utilization of the GAPC role as a negative regulator of autophagy.

Knockout of a rice K5.2 gene increases Ca accumulation in the grain

Rice is a staple food for half of the world’s population,but it is a poor dietary source of calcium(Ca)due to the low concentration.It is an important issue to boost Ca concentration in this grain to improve Ca deficiency risk,but the mechanisms underlying Ca accumulation are poorly understood.Here,we obtained a rice(Oryza sativa)mutant with high shoot Ca accumulation.The mutant exhibited 26%-53% higher Ca in shoots than did wild-type rice(WT)at different Ca supplies.Ca concentration in the xylem sap was 36% higher in the mutant than in the WT.There was no difference in agronomic traits between the WT and mutant,but the mutant showed 25% higher Ca in the polished grain compared with the WT.Map-based cloning combined with a complementation test revealed that the mutant phenotype was caused by an 18-bp deletion of a gene,OsK5.2,belonging to the Shaker-like K+channel family.OsK5.2 was highly expressed in the mature region of the roots and its expression in the roots was not affected by Ca levels,but upregulated by low K.Immunostaining showed that OsK5.2 was mainly expressed in the pericycle of the roots.Taken together,our results revealed a novel role for OsK5.2 in Ca translocation in rice,and will be a good target for Ca biofortification in rice.

The ferroxidases LPR1 and LPR2 control iron translocation in the xylem of Arabidopsis plants

Iron(Fe)deficiency is common in agricultural crops and affects millions of people worldwide.Translocation of Fe in the xylem is a key step for Fe distribution in plants.The mechanism controlling this process remains largely unknown.Here,we report that two Arabidopsis ferroxidases,LPR1 and LPR2,play a crucial and redundant role in controlling Fe translocation in the xylem.LPR1 and LPR2 are mainly localized in the cell walls of xylem vessels and the surrounding cells in roots,leaves,and stems.Knockout of both LPR1 and LPR2 increased the proportion of Fe(II)in the xylem sap,and caused Fe deposition along the vascular bundles especially in the petioles and main veins of leaves,which was alleviated by blocking blue light.The lpr1 lpr2 double mutant displayed constitutive expression of Fe deficiency response genes and overaccumulation of Fe in the roots and mature leaves under Fe-sufficient supply,but Fe deficiency chlorosis in the new leaves and inflorescences under low Fe supply.Moreover,the lpr1 lpr2 double mutant showed lower Fe concentrations in the xylem and phloem saps,and impaired 57Fe translocation along the xylem.In vitro assays showed that Fe(III)-citrate,the main form of Fe in xylem sap,is easily photoreduced to Fe(II)-citrate,which is unstable and prone to adsorption by cell walls.Taken together,these results indicate that LPR1 and LPR2 are required to oxidize Fe(II)and maintain Fe(III)-citrate stability and mobility during xylem translocation against photoreduction.Our study not only uncovers an essential physiological role of LPR1 and LPR2 but also reveals a new mechanism by which plants maintain Fe mobility during long-distance translocation in the xylem.

Plant Nutrition for Human Nutrition:Hints from Rice Research and Future Perspectives

Both plants and humans require mineral elements for their healthy growth and development.Mineral elements in the soil are taken up by the plant roots and transported to the edible parts for human consumption through various different transporters.An ideal future crop for human health should be rich in essential mineral elements but with less toxic elements in the edible parts.However,due to the great difference in the numbers and amounts of mineral elements required between plants and humans,it is a challenge to balance plant growth and nutrient requirement for humans.In this article,we mainly focus on the transport system of mineral elements from soil to grain in rice,a staple food for half of the world's population,and discuss recent progress on the underlying genetic and physiological mechanisms.Examples are given for silicon,zinc,and iron essential/beneficial for both plants and humans,selenium and iodine only essential for humans,and toxic cadmium and arsenic for all organisms.Manipulation of some transporters for these elements,especially those localized in the node for allocation of mineral elements to the grain,has been successful in generating rice with higher density and bioavailability of essential elements but with less accumulation of toxic elements.We provide our perspectives toward breeding future crops for human health.

Molecular evidence for biochemical diversification of phenolamide biosynthesis in rice plants

Two phenolamides （PAs）, p-coumaroylputrescine and feruloylputrescine strongly accumulate in rice （Oryza sativa cv. Nipponbare） leaves subjected to attack of chewing and sucking herbivores. Here we identified and characterized in vitro three novel rice genes that mediated coumaroyI-CoA/ feruloyI-CoA conjugation to polyamines, putrescine and agmatine. Interestingly, two genes were highly specific for their polyamine substrates, encoding putresdne N-hydrox- ycinnamoyltransferase and agmatine N-hydroxycinnamoyl- transferase, while the third enzyme could use both polyamines and it was therefore annotated as putrescine/ agmatine N-hydroxycinnamoyltransferase. All genes were preferentially expressed in rice roots and developing flowers, and in addition, the putrescine/agmatine N-hydroxycinnamoyl- transferase transcripts were strongly induced by wounding in the young rice leaves. Because the wound response of this gene was only partially suppressed in the jasmonoyI-L-isoleucine deficient plants （Osjarl）, it suggests that its upregulation （as well as inducible PAs in rice） may be largely independent of jasmonoyI-L-isoleucine signaling pathway. The finding of three closely related genes with a similar and/or overlapping activity in PA biosynthesis provides another striking example of rapid diversification of plant metabolism in response to environmental stresses in nature.

Response of Rice to Insect Elicitors and the Role of OsJAR1 in Wound and Herbivory-Induced JA-lle Accumulation

Plants produce jasmonic acid （JA） and its amino acid conjugate, jasmonoyI-L-isoleucine （JA-Ile） as major defense signals in response to wounding and herbivory. In rice （Oryza sativa）, JA and JA-Ile rapidly increased after mechanical damage, and this increase was further amplified when the wounds were treated with oral secretions from generalist herbivore larvae, lawn armyworms （Spodoptera mauritia）, revealing for the first time active perception mechanisms of herbivore-associated elicitor（s） in rice. In the rice genome, two OsJAR genes can conjugate JA and lie and form JA-Ile in vitro; however, their function in herbivory- induced accumulation of JA-Ile has not been investigated. By functional characterization of TOS17 retrotransposon-tagged Osjarl plants and their response to simulated herbivory, we show that OsJAR1 is essential for JA-Ile production in herbivore-attacked, field-grown plants. In addition, OsJAR1 was required for normal seed development in rice under field conditions. Our results suggest that OsJAR1 possesses at least two major functions in rice defense and development that cannot be complemented by the additional OsJAR2 gene function, although this gene previously showed overlapping enzyme activity in vitro.

To Gate, or Not to Gate： Regulatory Mechanisms for Intercellular Protein Transport and Virus Movement in Plants

Cell-to-cell signal transduction is vital for orchestrating the whole-body physiology of multi-cellular organ- isms, and many endogenous macromolecules, proteins, and nucleic acids function as such transported signals. In plants, many of these molecules are transported through plasmodesmata （Pd）, the cell wall-spanning channel structures that interconnect plant cells. Furthermore, Pd also act as conduits for cell-to-cell movement of most plant viruses that have evolved to pirate these channels to spread the infection. Pd transport is presumed to be highly selective, and only a limited repertoire of molecules is transported through these channels. Recent studies have begun to unravel mechanisms that actively regulate the opening of the Pd channel to allow traffic. This macromolecular transport between cells comprises two consecutive steps： intracellular targeting to Pd and translocation through the channel to the adjacent cell. Here, we review the current knowledge of molecular species that are transported though Pd and the mechanisms that control this traffic. Generally, Pd traffic can occur by passive diffusion through the trans-Pd cytoplasm or through the membrane/lu- men of the trans-Pd ER, or by active transport that includes protein-protein interactions. It is this latter mode of Pd trans- port that is involved in intercellular traffic of most signal molecules and is regulated by distinct and sometimes interdependent mechanisms, which represent the focus of this article.

Integrated view of plant metabolic defense with particular focus on chewing herbivores

Success of plants largely depends on their ability to defend against herbivores.Since emergence of the first voracious consumers,plants maintained adapting their structures and chemistry to escape from extinction.The constant pressure was further accelerated by adaptation of herbivores to plant defenses,which all together sparked the rise of a chemical empire comprised of thousands of specialized metabolites currently found in plants.Metabolic diversity in the plant kingdom is truly amazing,and although many plant metabolites have already been identified,a large number of potentially useful chemicals remain unexplored in plant bioresources.Similarly,biosynthetic routes for plant metabolites involve many enzymes,some of which still wait for identification and biochemical characterization.Moreover,regulatory mechanisms that control gene expression and enzyme activities in specialized metabolism of plants are scarcely known.Finally,understanding of how plant defense chemicals exert their toxicity and/or repellency against herbivores remains limited to typical examples,such as proteinase inhibitors,cyanogenic compounds and nicotine.In this review,we attempt summarizing the current status quo in metabolic defense of plants that is predominantly based on the survey of ubiquitous examples of plant interactions with chewing herbivores.

Exome-wide variation in a diverse barley panel reveals genetic associations with ten agronomic traits in Eastern landraces

Barley(Hordeum vulgare ssp.vulgare)is one of the first crops to be domesticated and is adapted to a wide range of environments.Worldwide barley germplasm collections possess valuable allelic variations that could further improve barley productivity.Although barley genomics has offered a global picture of allelic variation among varieties and its association with various agronomic traits,polymorphisms from East Asian varieties remain scarce.In this study,we analyze exome polymorphisms in a panel of 274 barley varieties collected worldwide,including 137 varieties from East Asian countries and Ethiopia.We reveal the underlying population structure and conduct genome-wide association studies for 10 agronomic traits.Moreover,we examin genome-wide associations for traits related to grain size such as awn length and glume length.Our results demonstrate the value of diverse barley germplasm panels containing Eastern varieties,highlighting their distinct genomic signatures relative to Western subpopulations.

ART1 and putrescine contribute to rice aluminum resistance via OsMYB30 in cell wall modification

Cell wall is the first physical barrier to aluminum(Al)toxicity.Modification of cell wall properties to change its binding capacity to Al is one of the major strategies for plant Al resistance;nevertheless,how it is regulated in rice remains largely unknown.In this study,we show that exogenous application of putrescines(Put)could significantly restore the Al resistance of art1,a rice mutant lacking the central regulator Al RESISTANCE TRANSCRIPTION FACTOR 1(ART1),and reduce its Al accumulation particularly in the cell wall of root tips.Based on RNA-sequencing,yeast-onehybrid and electrophoresis mobility shift assays,we identified an R2R3 MYB transcription factor OsMYB30 as the novel target in both ART1-dependent and Put-promoted Al resistance.Furthermore,transient dual-luciferase assay showed that ART1 directly inhibited the expression of OsMYB30,and in turn repressed Os4CL5-dependent 4-coumaric acid accumulation,hence reducing the Al-binding capacity of cell wall and enhancing Al resistance.Additionally,Put repressed OsMYB30 expression by eliminating Alinduced H2O2accumulation,while exogenous H2O2promoted OsMYB30 expression.We concluded that ART1 confers Put-promoted Al resistance via repression of OsMYB30-regulated modification of cell wall properties in rice.

Knockout of a gene encoding a Gγ protein boosts alkaline tolerance in cereal crops

Sorghum is highly tolerant to alkaline stress,but the underlying mechanisms are not well understood.Here,based on genotypic difference in alkaline tolerance of sorghum,it was found that AT1(Alkaline tolerance 1)encoding a G protein is involved in alkaline tolerance through negatively modulating the phosphorylation level of PIP2,an aquaporin with transport activity for H_(2)O_(2).Knockout of AT1 releases its inhibition of PIP2,thereby resulting in an increased transport of H_(2)O_(2)from the cytosol into the apoplast,subsequently boosting alkaline tolerance.

Defective Etioplasts Observed in Variegation Mutants May Reveal the Light-Independent Regulation of White/Yellow Sectors of Arabidopsis Leaves

Leaf variegation resulting from nuclear gene mutations has been used as a model system to elucidate the molecular mechanisms of chloroplast development. Since most variegation genes also function in photosynthesis, it remains unknown whether their roles in photosynthesis and chloroplast development are distinct. Here, using the variegation mutant thylakoid formation1 （thfl） we show that variegation formation is light independent. It was found that slow and uneven chloroplast development in thfl can be attributed to defects in etioplast development in darkness. Ultrastructural analysis showed the coexistence of plastids with or without prolamellar bodies （PLB） in cells of thfl, but not of WT. Although THF1 mutation leads to significant decreases in the levels of Pchlide and Pchliide oxidoreductase （POR） expression, genetic and 5-aminolevulinic acid （ALA）-feeding analysis did not reveal Pchlide or POR to be critical factors for etioplast formation in thfl. Northern blot analysis showed that plastid gene expression is dramatically reduced in thfl compared with that in WT, particularly in the dark. Our results also indicate that chlorophyll biosynthesis and expression of plastidic genes are coordinately suppressed in thfl. Based on these results, we propose a model to explain leaf variegation formation from the plastid development perspective.

Vascular Cambium-Localized AtSPDT Mediates Xylem-to-Phloem Transfer of Phosphorus for Its Preferential Distribution in Arabidopsis

During plant growth and development mineral elements are preferentially delivered to different organs and tissues to meet the differential demand. It has been shown that the preferential distribution of mineral nutrients in gramineous plants is mediated by node-based transporters, but the mechanisms of preferential distribution in dicots are poorly understood. Here, we report a distinct mechanism for the preferential distribution of phosphorus (P) in Arabidopsis plants, revealed by detailed functional analysis of AtSPDT/AtSULTR3;4 (SULTR-like P Distribution Transporter), a homolog of rice OsSPDT. Like OsSPDT, AtSPDT is localized at the plasma membrane and showed proton-dependent transport activity for P. Interestingly, we found that AtSPDT is mainly expressed in the rosette basal region and leaf petiole, and its expression is up-regulated by P deficiency. Tissue-specific analysis showed that AtSPDT is mainly located in the vascular cambium of different organs, as well as in the parenchyma tissues of both xylem and phloem regions. Knockout of AtSPDT inhibited the growth of new leaves under low P due to decreased P distribution to those organs. The seed yields of the wild-type and atspdt mutant plants are similar, but the seeds of mutant plants contain – less P. These results indicate that AtSPDT localized in the vascular cambium is involved in preferential distribution of P to the developing tissues, through xylem-to-phloem transfer mainly at the rosette basal region and leaf petiole.

Essentials of Proteolytic Machineries in Chloroplasts

Plastids are unique organelles that can alter their structure and function in response to environmental and developmental stimuli. Chloroplasts are one type of plastid and are the sites for various metabolic pro- cesses, including photosynthesis. For optimal photosynthetic activity, the chloroplast proteome must be properly shaped and maintained through regulated proteolysis and protein quality control mechanisms. Enzymatic functions and activities are conferred by protein maturation processes involving consecutive proteolytic reactions. Protein abundances are optimized by the balanced protein synthesis and degrada- tion, which is depending on the metabolic status. Malfunctioning proteins are promptly degraded. Twenty chloroplast proteolytic machineries have been characterized to date. Specifically, processing peptidases and energy-driven processive proteases are the major players in chloroplast proteome biogenesis, remod- eling, and maintenance. Recently identified putative proteases are potential regulators of photosynthetic functions. Here we provide an updated, comprehensive overview of chloroplast protein degradation ma- chineries and discuss their importance for photosynthesis. Wherever possible, we also provide structural insights into chloroplast proteases that implement regulated proteolysis of substrate proteins/peptides.

Farinose fiavonoids are associated with high freezing tolerance in fairy primrose (Primula malacoides) plants

The deposition of surface （farinose） flavonoids on aerial parts of some Primula species is a well-documented but poorly understood phenomenon. Here, we show that flavonoid deposition on the leaves and winter buds may contribute strongly to preventing freezing damage in these plants. The ice nucleation temperature of fairy primrose （Primula malacoides） leaves covered with natural flavone was approximately 6~C lower compared to those that had their flavone artificially removed. Additionally, farinose flavonoids on the leaves reduced subse- quent electrolyte leakage （EL） from the cells exposed to freezing temperatures. Interestingly, exogenous application of flavone at 4 mg/g fresh weight to P. malacoides leaves, which had the original flavone mechanically removed, restored freezing tolerance, and diminished EL from the cells to pretreatment values. Our results suggest that farinose flavonoids may function as mediators of freezing tolerance in P. malacoides, and exogenous application of flavone could be used to reduce freezing damage during sudden but predictable frost events in other plant species.

Improving disease resistance to rice false smut without yield penalty by manipulating the expression of effector target

Rice grain production and quality are threatened by many devastating diseases.False smut caused by Ustilaginoidea virens is emerging as a major fungal disease of rice,leading to a severe loss of yield.U.virens invades only rice panicles at the late stage of booting and replaces grains with false smut balls containing mycotoxins,which endanger human and animal health(Sun et al.,2020).This successful colonization is accomplished through manipulating host immune responses by U.virens effectors.

Phototropin-and photosynthesis-dependent mitochondrial positioning in Arabidopsis thaliana mesophyll cells^FA

Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic in-teractions. We previously reported that, in leaf palisade cel s of Arabidopsis thaliana, mitochondria exhibit blue-light-dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue-light receptor phototropins. In this study, precise motility analyses by fluorescent micro-scopy revealed that the individual mitochondria in palisade cel s, labeled with green fluorescent protein, exhibit typical stop-and-go movement. When exposed to blue light, the velocity of moving mitochondria increased in 30 min, whereas after 4 h, the frequency of stoppage of mi-tochondrial movement markedly increased. Using different mutant plants, we concluded that the presence of both phototropin1 and phototropin2 is necessary for the early acceleration of mitochondrial movement. On the contrary, the late enhancement of stoppage of mitochondrial movement occurs only in the presence of phototropin2 and only when intact photosynthesis takes place. A plasma-membrane ghost assay suggested that the stopped mi-tochondria are firmly adhered to chloroplasts. These re-sults indicate that the physical interaction between mi-tochondria and chloroplasts is cooperatively mediated by phototropin2- and photosynthesis-dependent signals. The present study might add novel regulatory mechanism for light-dependent plant organel e interactions.

LATERAL ROOTLESS2, a Cyclophilin Protein, Regulates Lateral Root Initiation and Auxin Signaling Pathway in Rice

Dear Editor, Cyclophilins （CYP） are a class of highly conserved pepti- dyl-prolyl cis-trans isomerases （PPlases） that play important roles in various biological processes in eukaryotes （reviewed in Romano et al. （2004））. In higher plants, a conserved sin- gle domain cyclophilin has been identified as a novel com- ponent of the auxin signaling pathway by analyzing the tomato diageotropica （dgt） mutant （Ivanchenko et al., 2006; Oh et al., 2006）. The dgt mutant displays a lateral-rootless and auxin-resistant phenotype （Ivanchenko et aL, 2006）. Further studies revealed that mutations in the DGT-like genes of Physcomitrella patens also exhibited an auxin-resistant phenotype, suggesting a conserved role of DGT-like proteins in auxin signaling. Moreover,