Auxin-brassinosteroid crosstalk:Regulating rice plant architecture and grain shape

Rice(Oryza sativa)plant architecture and grain shape,which determine grain quality and yield,are modulatedby auxin and brassinosteroid via regulation of cell elongation and proliferation.We review the signaltransduction of these hormones and the crosstalk between their signals on the regulation of rice plantarchitecture and grain shape.

Utilizing auxin dwarf genes to optimize seed yield and lodging resistance in rapeseed

Direct-seeding rapeseed production at high plant density raises the risk of lodging.We investigated the use of dwarf genes to improve rapeseed plant architecture to balance yield and lodging.Three genotypes with different plant architectures(dwarf sca^(HS5),semi-dwarf+/sca^(HS5),and tall ^(HS5))were evaluated under varying nitrogen rates(N1,N2,and N3:120,240,and 360 kg N ha^(-1))and plant densities(D1,D2,and D3:15,45,and 75 plants m^(-2))from 2019 to 2022.The results showed that increasing N rate positively influenced yield while decreasing lodging resistance in all genotypes.Increasing plant density(D2-D3)enhanced lodging resistance and yield in sca^(HS5) and+/sca^(HS5),but reduced yield in ^(HS5).Compared to the two parents,+/sca^(HS5) exhibited moderate expressions of IAA3,GH3.15,and SAUR30 in stems under N2D3,resulting in reduced plant height and increased compactness.Additionally,+/sca^(HS5) had a thicker silique layer than ^(HS5) by 14.7%,and it had a significant correlation between branch height/angle and yield.Increasing N rate led to increased lignin and pectin contents,while cellulose content decreased.Increasing plant density resulted in greater stem cellulose content and CSLA3/7 expression in sca^(HS5) and+/sca^(HS5),but decreased in ^(HS5).Compared to ^(HS5),+/sca^(HS5) exhibited higher expressions of ARAD1 and GAUT4,along with a 51.1%increase in pectin content,leading to improved lodging resistance under N2D3.Consequently,+/sca^(HS5) showed a 46.4%higher yield and 38.9%lodging resistance than ^(HS5) under N2D3,while sca^(HS5) demonstrated strong lodging resistance but lower yield potential.Overall,this study underscores the potential of utilizing auxin dwarf genes to optimize the trade-off between yield and lodging resistance in rapeseed and the possibility of maximizing yield potential by optimizing the plant architecture of+/sca^(HS5) through nitrogen reduction and dense planting.

Advances in the study of auxin early response genes:Aux/IAA,GH3,and SAUR

Auxin plays a crucial role in all aspects of plant growth and development.Auxin can induce the rapid and efficient expression of some genes,which are named auxin early response genes(AERGs),mainly including the three families:auxin/indole-3-acetic acid(Aux/IAA),Gretchen Hagen 3(GH3),and small auxin-up RNA(SAUR).Aux/IAA encodes the Aux/IAA protein,which is a negative regulator of auxin response.Aux/IAA and auxin response factor(ARF)form a heterodimer and participate in a variety of physiological processes through classical or non-classical auxin signaling pathways.The GH3 encodes auxin amide synthetase,which catalyzes the binding of auxin to acyl-containing small molecule substrates(such as amino acids and jasmonic acid),and regulates plant growth and stresses by regulating auxin homeostasis.SAURs is a class of small auxin up-regulated RNAs.SAUR response to auxin is complex,and the process may occur at the transcriptional,post-transcriptional and protein levels.With the development of multi-omics,significant progress has been made in the study of Aux/IAA,GH3,and SAUR genes,but there are still many unknowns.This review offers insight into the characteristics of Aux/IAA,GH3,and SAUR gene families,and their roles in roots,hypocotyls,leaves,leaf inclinations,flowers,seed development,stress response,and phytohormone crosstalk,and provides clues for future research on phytohormone signaling and the molecular design breeding of crops.

The role of the auxin-response genes MdGH3.1 and MdSAUR36 in bitter pit formation in apple

Apples often exhibit bitter pits in response to metabolic disorders during ripening and storage;however, the mechanisms underlying the bitter pit(BP) development remain unclear. Here, metabolome and transcriptome analyses were performed to investigate BP pulp of 'Fuji'. Two auxin-response genes, MdGH3.1 and MdSAUR36, were screened. Their expression as well as the auxin content in BP pulp were found to be higher than those in healthy pulp(P < 0.01). In the field, excess CO(NH2)2increased the incidence of BP. Moreover, the auxin content and MdGH3.1 expression increased in apples after nitrogen fertilization. On Day 30 before harvest, the two genes were transiently transferred to the fruit, and 20.69% and 23.21% of BP fruits were harvested. After 10 μmol·L-1auxin was infiltrated at low pressure into postharvest fruit, the increase in MdGH3.1 expression occurred earlier than that in MdSAUR36. MdGH3.1 increased the expression of MdSAUR36, but MdSAUR36 did not increase expression of MdGH3.1. Therefore, we suggest that MdGH3.1 acts upstream of MdSAUR36 during BP formation and that these genes induce BP formation by regulating auxin and phenylpropanoid biosynthesis.

Silencing of early auxin responsive genes MdGH3-2/12 reduces the resistance to Fusarium solani in apple

Apple replant disease(ARD)has led to severe yield and quality reduction in the apple industry.Fusarium solani(F.solani)has been identified as one of the main microbial pathogens responsible for ARD.Auxin(indole-3-acetic acid,IAA),an endogenous hormone in plants,is involved in almost all plant growth and development processes and plays a role in plant immunity against pathogens.Gretchen Hagen3(GH3)is one of the early/primary auxin response genes.The aim of this study was to evaluate the function of MdGH3-2 and MdGH3-12 in the defense response of F.solani by treating MdGH3-2/12 RNAi plants with F.solani.The results show that under F.solani infection,RNAi of MdGH3-2/12 inhibited plant biomass accumulation and exacerbated root damage.After inoculation with F.solani,MdGH3-2/12 RNAi inhibited the biosynthesis of acid-amido synthetase.This led to the inhibition of free IAA combining with amino acids,resulting in excessive free IAA accumulation.This excessive free IAA altered plant tissue structure,accelerated fungal hyphal invasion,reduced the activity of antioxidant enzymes(SOD,POD and CAT),increased the reactive oxygen species(ROS)level,and reduced total chlorophyll content and photosynthetic ability,while regulating the expression of PR-related genes including PR1,PR4,PR5 and PR8.It also changed the contents of plant hormones and amino acids,and ultimately reduced the resistance to F.solani.In conclusion,these results demonstrate that MdGH3-2 and MdGH3-12 play an important role in apple tolerance to F.solani and ARD.

Overexpression of auxin/indole-3-acetic acid gene MdIAA24 enhances Glomerella leaf spot resistance in apple(Malus domestica)

Auxin is throughout the entire life process of plants and is involved in the crosstalk with other hormones,yet its role in apple disease resistance remains unclear.In this study,we investigated the function of auxin/indole-3-acetic acid(IAA)gene Md IAA24 overexpression in enhancing apple resistance to Glomerella leaf spot(GLS)caused by Colletotrichum fructicola(Cf).Analysis revealed that,upon Cf infection,35S::Md IAA24 plants exhibited enhanced superoxide dismutase(SOD)and peroxidase(POD)activity,as well as a greater amount of glutathione(reduced form)and ascorbic acid accumulation,resulting in less H_(2)O_(2)and superoxide anion(O_(2)^(-))in apple leaves.Furthermore,35S::Md IAA24 plants produced more protocatechuic acid,proanthocyanidins B1,proanthocyanidins B2 and chlorogenic acid when infected with Cf.Following Cf infection,35S::Md IAA24 plants presented lower levels of IAA and jasmonic acid(JA),but higher levels of salicylic acid(SA),along with the expression of related genes.The overexpression of Md IAA24 was observed to enhance the activity of chitinase andβ-1,3-glucanase in Cfinfected leaves.The results indicated the ability of Md IAA24 to regulate the crosstalk between IAA,JA and SA,and to improve reactive oxygen species(ROS)scavenging and defense-related enzymes activity.This jointly contributed to GLS resistance in apple.

Carbon Monoxide Modulates Auxin Transport and Nitric Oxide Signaling in Plants under Iron Deficiency Stress

Carbon monoxide(CO)and nitric oxide(NO)are signal molecules that enhance plant adaptation to environmental stimuli.Auxin is an essential phytohormone for plant growth and development.CO and NO play crucial roles in modulating the plant’s response to iron deficiency.Iron deficiency leads to an increase in the activity of heme oxygenase(HO)and the subsequent generation of CO.Additionally,it alters the polar subcellular distribution of Pin-Formed 1(PIN1)proteins,resulting in enhanced auxin transport.This alteration,in turn,leads to an increase in NO accumulation.Furthermore,iron deficiency enhances the activity of ferric chelate reductase(FCR),as well as the expression of the Fer-like iron deficiency-induced transcription factor 1(FIT)and the ferric reduction oxidase 2(FRO2)genes in plant roots.Overexpression of the long hypocotyl 1(HY1)gene,which encodes heme oxygenase,or the CO donor treatment resulted in enhanced basipetal auxin transport,higher FCR activity,and the expression of FIT and FRO2 genes under Fe deficiency.Here,a potential mechanism is proposed:CO and NO interact with auxin to address iron deficiency stress.CO alters auxin transport,enhancing its accumulation in roots and up-regulating key iron-related genes like FRO2 and IRT1.Elevated auxin levels affect NO signaling,leading to greater sensitivity in root development.This interplay promotes FCR activity,which is crucial for iron absorption.Together,these molecules enhance iron uptake and root growth,revealing a novel aspect of plant physiology in adapting to environmental stress.

Camellia sinensis CsMYB4a participates in regulation of stamen growth by interaction with auxin signaling transduction repressor CsAUX/IAA4

Subgroup 4(Sg4)members of the R2R3-MYB are generally known as negative regulators of the phenylpropanoid pathway in plants.Our previous research showed that a R2R3-MYB Sg4 member from Camellia sinensis(CsMYB4a)inhibits expression of some genes in the phenylpropanoid pathway,but its physiological function in the tea plant remained unknown.Here,CsMYB4a was found to be highly expressed in anther and filaments,and participated in regulating filament growth.Transcriptome analysis and exogenous auxin treatment showed that the target of CsMYB4a might be the auxin signal pathway.Auxin/indole-3-acetic acid 4(AUX/IAA4),a repressor in auxin signal transduction,was detected from a yeast two-hybrid screen using CsMYB4a as bait.Gene silencing assays showed that both CsIAA4 and CsMYB4a regulate filament growth.Tobacco plants overexpressing CsIAA4 were insensitive to exogenous a-NAA,consistent with overexpression of CsMYB4a.Protein-protein interaction experiments revealed that CsMYB4a interacts with N-terminal of CsIAA4 to prevent CsIAA4 degradation.Knock out of the endogenous NtIAA4 gene,a CsIAA4 homolog,in tobacco alleviated filament growth inhibition and a-NAA insensitivity in plants overexpressing CsMYB4a.All results strongly suggest that CsMYB4a works synergistically with CsIAA4 and participates in regulation of the auxin pathway in stamen.

The nitrate-responsive transcription factor Md NLP7 regulates callus formation by modulating auxin response

Under appropriate culture conditions,plant cells can regenerate new organs or even whole plants.De novo organ regeneration is an excellent biological system,which usually requires additional growth regulators,including auxin and cytokinin.Nitrate is an essential nutrient element for plant vegetative and reproductive development.It has been reported that nitrate is involved in auxin biosynthesis and transport throughout the growth and development of plants.In this study,we demonstrated that the ectopic expression of the MdNLP7 transcription factor in Arabidopsis could regulate the regeneration of root explants.MdNLP7 mainly participated in the regulation of callus formation,starting with pericycle cell division,and mainly affected auxin distribution and accumulation in the regulation process.Moreover,MdNLP7 upregulated the expression of genes related to auxin biosynthesis and transport in the callus formation stage.The results demonstrated that MdNLP7 may play a role in the nitrate-modulated regeneration of root explants.Moreover,the results revealed that nitrate–auxin crosstalk is required for de novo callus initiation and clarified the mechanisms of organogenesis.

Genome-wide identification of apple auxin receptor family genes and functional characterization of MdAFB1

The auxin receptor(TIR1/AFBs)family encodes the F-box protein subunit,which is involved in the formation of the E3 ubiquitin ligase SCFTIR1/AFBs complex,a key component of the auxin signaling pathway.However,there are few studies on the auxin receptor family in apple(Malus×domestica).In this study,eight MdAFBs were identified,and phylogenetic analysis showed that they were classified into four groups and distributed on eight chromosomes.Herein,a comprehensive analysis of the MdAFB gene family was conducted to identify cis-acting elements,gene structures,protein structures,aligned sequences,conserved motifs,conserved amino acids,and the protein–protein interaction network.The results of yeast two-hybrid assays showed that MdAFB1 interacted with three auxin repressor proteins.The results of qRT-PCR showed that MdAFB1 responded to osmotic and salt stress.The overexpression of MdAFB1 increased osmotic and salt resistance in apple calli,and the ectopic expression of MdAFB1 enhanced osmotic and salt tolerance in Arabidopsis.This study provided a basis for the identification of auxin receptor genes in apple and their functions in mediating osmotic and salt stress.

Less hairy leaf 1,an RNaseH-like protein,regulates trichome formation in rice through auxin

The trichomes of rice leaves are formed by the differentiation and development of epidermal cells.Plant trichomes play an important role in stress resistance and protection against direct ultraviolet irradiation.However,the development of rice trichomes remains poorly understood.In this study,we conducted ethylmethane sulfonate(EMS)-mediated mutagenesis on the wild-type(WT)indica rice‘Xida 1B’.Phenotypic analysis led to the screening of a mutant that is defective in trichome development,designated lhl1(less hairy leaf 1).We performed map-based cloning and localized the mutated gene to the 70-kb interval between the molecular markers V-9 and V-10 on chromosome 2.The locus LOC_Os02g25230 was identified as the candidate gene by sequencing.We constructed RNA interference(LHL1-RNAi)and overexpression lines(LHL1-OE)to verity the candidate gene.The leaves of the LHL1-RNAi lines showed the same trichome developmental defects as the lhl1 mutant,whereas the trichome morphology on the leaf surface of the LHL1-OE lines was similar to that of the WT,although the number of trichomes was significantly higher.Quantitative real-time PCR(RT-qPCR)analysis revealed that the expression levels of auxin-related genes and positive regulators of trichome development in the lhl1 mutant were down-regulated compared with the WT.Hormone response analysis revealed that LHL1 expression was affected by auxin.The results indicate that the influence of LHL1 on trichome development in rice leaves may be associated with an auxin pathway.

The HD-Zip transcription factor GhHB12 represses plant height by regulating the auxin signaling in cotton

Upland cotton(Gossypium hirsutum L.)is the most important natural textile fiber crop worldwide.Plant height(PH)is a significant component of plant architecture,strongly influencing crop cultivation patterns,overall yield,and economic coefficient.However,cotton genes regulating plant height have not been fully identified.Previously,an HD-Zip gene(GhHB12)was isolated and characterized in cotton,which regulates the abiotic and biotic stress responses and the growth and development processes.In this study,we showed that GhHB12 was induced by auxin.Moreover,overexpression of GhHB12 induces the expression of HY5,ATH1,and HAT4,represses the spatial-temporal distribution,polar transport,and signaling of auxin,alters the expression of genes involved in cell wall expansion,and restrains the plant height in cotton.These results suggest a role of GhHB12 in regulating cotton plant height,which could be achieved by affecting the auxin signaling and cell wall expansion.

Transcriptome Analysis of Auxin Drives Cone Size Regulation in Fokienia hodginsii

As the reproductive organ of the endangered species Fokienia hodginsii,the size of the cones is a constraint on the reproductive renewal of the population.In this study,the molecular basis of the influence of cone size on F.hodginsii was elucidated by comparing the phenotype,biochemistry,and transcriptome of two cultivars of F.hodginsii(‘FJ431’and‘FJ415’).The two cultivars differed significantly in cone size,with FJ431 having a significantly larger cone size and weight than FJ415,1.32 and 1.90 times that of FJ415,respectively.RNA-Seq analysis of both cultivars retrieved 75,940 genes whose approximate functions were classified as the pathway of response to endogenous stimulus and response to hormone and showed significant differences in the auxin-activated signaling pathway,particularly the MAPK signaling pathway-plant.Furthermore,the endogenous IAA content was significantly higher in FJ431 than in FJ415,and 1.58 and 1.29 times more IAA was present in immature and mature cones,respectively.Moreover,exogenous IAA treatment significantly induced the expression of the MAPK pathway-related gene TRINITY_DN10564_c0_g1 and significantly inhibited the expression of the MAPK pathwayrelated gene TRINITY_DN17056_c0_g1.Our work suggests that IAA can affect the cone size of F.hodginsii,most probably through the MAPK pathway.This has high theoretical and practical significance for the improvement of genetic breeding and the further cultivation of quality germplasm resources of F.hodginsii.

Light Promotes Protein Stability of Auxin Response Factor 7#

Light is an environmental signaling,whereas Aux/IAA proteins and Auxin Response Factors(ARFs)are regulators of auxin signalling.Aux/IAA proteins are unstable,and their degradation dependents on 26S ubiquitin-proteasome and is promoted by Auxin.Auxin binds directly to a SCF-type ubiquitin-protein ligase,TIR1,facilitates the interaction between Aux/IAA proteins and TIR1,and then the degradation of Aux/IAA proteins.A few studies have reported that some ARFs are also unstable proteins,and their degradation is also mediated by 26S proteasome.In this study,by using of antibodies recognizing endogenous ARF7 proteins,we found that protein stability of ARF7 was affected by light.By expressing MYC tagged ARF activators in protoplasts,we found that degradation of ARF7 was inhibited by 26 proteasome inhibitors.In addition,at least ARF5 and ARF19 were also unstable proteins,and degradation of ARF5 via 26S proteasome was further confirmed by using stable transformed plants overexpressing ARF5 with a GUS tag.

Evidence That the Auxin Signaling Pathway Interacts with Plant Stress Response

Auxin influences a variety of developmental and physiological processes. Early reports, suggested that auxin might affect plant stress response. We have identified a number of auxin responsive genes in Arabidopsis thaliana (L.) Heynh. by using cDNA an-ay and found that stress responsive genes, such as,Arabidopsis homolog of MEK kinase 1 (ATMEKK1), ReL/SpoT homolog 3 ( At-RSH3), Catalase 1 ( Cat1) and Ferritin 1 (Fer1), were down-regulated by auxin, indicating that auxin regulates ale expression of stress responsive genes. We also demonstrated that nitrilase genes, nitrilase I ( NIT]) and nitrilase 2 (NIT2) involving in indole-3-acetic acid (IAA) biosynthesis, were induced by salinity stress, suggesting that the level of IAA might increase in response to salinity stress. To dissect the signal pathway involved in the interaction, two auxin insensitive mutants, auxin resistant 2 (axr2) and auxin resistant 1-3 (axrl-3) were used. Stress responsive genes were induced by salt stress in wild type and axr2, but not in axr1-3. The result suggests that die interaction between auxin and stress responses may be linked in the ubiquitin pathway.

Effects of Different Kinds of Exogenous Auxin on the Growth of Rice Roots under Cadmium Stress

[Objective] The aim was to study the effect of different kinds of exogenous auxin on the growth of rice roots under cadmium stress.[Method] Oryza sativa L.cv Zhonghua No.11 was used as experimental materials to detect the effect of different kinds of exogenous auxin on the growth of rice roots.[Result] The results showed that 0.1 mmol/L Cd treatment could not only increase primary,adventitious and lateral root length but also lateral root number,whereas the shoot growth was inhibited.When supplemented with different concentrations of NAA,IAA,IBA and 2,4-D,the growth of root system varied and similar change trend had been found.At the auxin concentration of 10^-9-10^-7 mol/L in particular 10^-8 mol/L,all four kinds of auxin promoted the elongation growth of primary and adventitious roots,but inhibition was observed when auxin was higher than 10^-7 mol/L.The decreased shoot growth caused by Cd could not be counteracted by supplementing with the four kinds of auxin.However,at the auxin concentration of 10^-9-10^-8 mol/L,NAA could improve rice growth under Cd stress condition.The formation and development of lateral roots on primary and adventitious roots was not only similar but also different after applying the same concentration of four auxins.[Conclusion] The addition of suitable amount of auxin under cadmium stress （such as 10^-9-10^-8 mol/L of NAA and so on） could ease the damage of cadmium on plants to a certain extent.

Quercetin Promotes Auxin Transport in Arabidopsis thaliana

Study on the role of quereentin in polar auxin transportation. Arabidopsis was cultured on medium supplemented with quereetin to observe the growth of hypoeotyls, ^14C-IAA transport assays were conducted to measure the auxin transport activity. The results showed that Arabidopsis mutant auxl which had been deficient in auxin influx transportion obviously recovered the ability after eultured on the medium with quercetin. The polar auxin transport was promoted by the addition of quereetin. These results indicated that quereetin could promote polar auxin transport in vivo.

A Pin gene families encoding components of auxin efflux carriers in Brassica juncea

Based on the sequence information of Arabidopsis PIN1, two cDNAs encoding PIN homologues from Brassica juncea, Bjpin2 and Bjpin3, were isolated through cDNA library screening. Bjpin2 and Bjpin3 encoded proteins containing 640 and 635 amino acid residues, respectively, which shared 97.5% identities with each other and were highly homologous to Arabidopsis PIN1, PIN2 and other putative PIN proteins. BJPIN2 and BjPIN3 had similar structures as AtPIN proteins. Northern blot analysis indicated that Bjpin2 was expressed in stem, leaf and floral tissues, while Bjpin3 was expressed predominantly in stem and hypocotyls. Two promoter fragments of pin genes, Bjpin-X and Bjpin-Z, were isolated by 'genome walking' technique using primers at 5'-end of pin cDNA. Promoter-gus fusion studies revealed the GUS activities driven by Bjpin-X were at internal side of xylem and petal; while those driven by Bjpin-Z were detected at leaf vein, epidermal cell and cortex of stem, vascular tissues and anther. Results of the pin genes with different expression patterns in B. juncea suggested the presence of a gene family.

Transcript Profiles of Auxin Efflux Carrier and IAA-Amido Synthetase Genes Suggest the Role of Auxin on Apple (<i>Malus</i>×<i>domestica</i>) Fruit Maturation Patterns

Auxin has been suggested to play an essential role in regulating apple fruit maturation and ripening, though the molecular function of auxin and its interaction with ethylene during apple fruit development are largely unknown. To understand the function of auxin during apple fruit maturation and ripening, auxin efflux carrier and IAA-amido synthetase encoding genes were identified from the apple genome based on the results of previous microarray analysis. The expression patterns of these genes were analyzed using qRT-PCR during 10 - 12 weeks of fruit maturation for two apple cultivars: “Golden Delicious” (GD) and “Cripps Pink” (CP), which have the distinct patterns of maturation progression. Our results showed that the expressions of auxin efflux carrier and IAA-amido synthetase genes have a correlation with the timing of ethylene biosynthesis pathway activation in both cultivars. The earlier and stronger expression of MdGH3.102 and MdAECFP1 in the fruit of GD, a mid-season cultivar, correlates with the earlier activation of a pre-climacteric ethylene biosynthesis gene of MdACS3, compared with that in CP, a late-ripening apple cultivar. Results of exogenous IAA treatment indicated that the expression patterns of the genes were regulated in a fruit maturity dependent manner. Our results suggested that the dynamics of the auxin level in apple fruit cortex could be one of the key factors influencing the timing of ethylene biosynthesis pathway activation and consequently contributed to the control of the apple maturation progression.

Participation of Auxin Transport in the Early Response of the Arabidopsis Root System to Inoculation with Azospirillum brasilense

The potential of Plant Growth Promoting Rhizobacteria(PGPR)has been demonstrated in the case of plant inoculation with bacteria of the genus Azospirillum which improves yield.A.brasilense produces a wide variety of molecules,including the natural auxin indole-3-acetic acid(IAA),as well as other phytoregulators.However,several studies have suggested that auxin induces changes in plant development during their interaction with the bacteria.The effects of A.brasilense Sp245 on the development of Arabidopsis thaliana root were investigated to help explain the molecular basis of the interaction.The results obtained showed a decrease in primary root length from the first day and remained so throughout the exposure,accompanied by a stimulation of initiation and maturation of lateral root primordia and an increase of lateral roots.An enhanced auxin response was evident in the vascular tissue and lateral root meristems of inoculated plants.However,after five days of bacterization,the response disappeared in the primary root meristems.The role of polar auxin transport(PAT)in auxins relocation involved the PGP1,AXR4-1,and BEN2 proteins,which apparently mediated A.brasilense-induced root branching of Arabidopsis seedlings.