Transgenic expression of DwMYB2 impairs iron transport from root to shoot in Arabidopsis thaliana

In plant, iron uptake and homeostasis are tightly regulated to ensure its absorption from soil and to avoid excess iron in the cell. Many genes involved in this process have been identified during past several years, but there are many problems remain unsolved in the genetic regulation of whole plant iron trafficking and allocation. MYB transcription factors contain tandem repeats of a -50 amino acid DNA-binding motif （R） and are involved in the regulation of many aspects of plant development, hormone signaling and metabolism. Here, we report that the ectopic expression of orchid R2R3-MYB gene DwMYB2 in Arabidopsis thaliana confers the transgenic plants hypersensitivity to iron deficiency. In DwMYB2 transgenic plants, the iron content in root is two-fold higher compared to that in wild-type root, while the reverse is true in shoot. This imbalance of iron content in root and shoot suggested that the translocation of iron from root to shoot was affected by the expression of DwMYB2 in the transgenic plants. Consistently, gene chip and reverse transcription-polymerase chain reaction analysis revealed that the ferric-chelate reductase gene, AtFRO2, and the iron transporter gene, AtlRT1 and AtlRT2, are up-regulated by DwMYB2 expression, while other potential iron transporters such as AtlREG1, AtFRD3 and NRAMP1 are down-regulated. In addition, the expression of several putative peptide transporters and transcription factors are also altered in the 35S：：DwMYB2 transgenic lines. These data provide us insight into the whole plant translocation of iron and identify candidate genes for iron homeostasis in plants despite the fact that a heterologous gene was expressed.

Inaugural Editorial:Seed Biology

Seed is the most important reproductive organ in plant.Since its first emergence approximately 370 million years ago,seed plant had overwhelming advantage to non-seed plants in reproduction,spreading and colonization in terrestrial land.Beside its essential function in the sexual reproduction of plants,seed is the most economically important agricultural product,offering necessity food for human and wildlife,nutritious feed for livestock.Seeds and grains also provide massive amount of raw materials for manufactured goods,such as coffee,starch,and oil.Seeds also play a pivotal role in development of fruits which supplement significant portion of food and nutrition for human and wildlife.

Pollen-expressed RLCKs control pollen tube burst

In angiosperms,the pollen tube enters the receptive synergid cell,where it ruptures to release its cytoplasm along with two sperm cells.This interaction is complex,and the exact signal transducers that trigger the bursting of pollen tubes are not well understood.In this study,we identify three homologous receptor-like cytoplasmic kinases(RLCKs)expressed in pollen tubes of Arabidopsis,Delayed Burst 1/2/3(DEB1/2/3),which play a crucial role in this process.These genes produce proteins localized on the plasma membrane,and their knockout causes delayed pollen tube burst and entrance of additional pollen tubes into the embryo sac due to fertilization recovery.We show that DEBs interact with the Ca^(2+)pump ACA9,influencing the dynamics of cytoplasmic Ca^(2+)in pollen tubes through phosphorylation.These results highlight the importance of DEBs as key signal transducers and the critical function of the DEB-ACA9 axis in timely pollen tube burst in synergids.

RLKs orchestrate the signaling in plant male-female interaction

Different from animals, sessile plants are equipped with a large receptor-like kinase(RLK) superfamily. RLKs are a family of single trans-membrane proteins with divergent N-terminal extracellular domains capped by a signal peptide and C-terminal intracellular kinase. Researches in the last two decades have uncovered an increasing number of RLKs that regulate plant development, stress response and sexual reproduction, highlighting a dominant role of RLK signaling in cell-to-cell communications. Sexual reproduction in flowering plants is featured by interactions between the male gametophyte and the female tissues to facilitate sperm delivery and fertilization. Emerging evidences suggest that RLKs regulate almost every aspect of plant reproductive process, especially during pollination. Therefore, in this review we will focus mainly on the function and signaling of RLKs in plant male-female interaction and discuss the future prospects on these topics.

Receptor-like kinases take center stage in plant biology

Like the animals,higher plants must perceive and interpret numerous external and endogenous cues to properly program growth and development and physiological responses.Animal cells use diverse receptors to perceive external signals to regulate cellular processes.Thus,receptor-tyrosine kinases（RTKs）are responsible for perceiving growth regulators

TICKET attracts pollen tubes and mediates reproductive isolation between relative species in Brassicaceae

In flowering plants,pollen tubes are attracted to the ovule by secreted peptides to release the sperm cells for double fertilization.This process is species-specific and acts as an important stage of reproductive isolation between species.Here we identified a cysteine-rich peptide TICKET2 in Arabidopsis thaliana and its orthologs in Arabidopsis lyrata and Capsella rebella that can attract the conspecific pollen tubes,but not the pollen tubes of relative species in Brassicaceae.Genetic knockout of the AtTICKET subclade compromised the pollen tube attraction efficiency.This study identified a new pollen tube attracting signal and shed light on the molecular basis of reproductive isolation.

GAMETOPHYTIC FACTOR 1,Involved in Pre-mRNA Splicing,Is Essential for Megagametogenesis and Embryogenesis in Arabidopsis

RNA biogenesis is essential and vital for accurate expression of genes. It is obvious that cells cannot continue normal metabolism when RNA splicing is interfered with. sgt13018 is such a mutant, with partial loss of function of GAMETOPHYTIC FACTOR 1 （GFA1）; a gene likely involved in RNA biogenesis in Arabidopsis. The mutant is featured in the phenotype of diminished female gametophyte development at stage FG5 and is associated with the arrest of early embryo development in Arabidopsis. Bioinformatics data showed that homologs of gene GFA1 in yeast and human encode putative U5 snRNPspecific proteins required for pre-mRNA splicing. Furthermore, the result of yeast two-hybrid assay indicated that GFA1 physically interacted with AtBrr2 and AtPrp8, the putative U5 snRNP components, of Arabidopsis. This investigation suggests that GFA1 is involved in mRNA biogenesis through interaction with AtBrr2 and AtPrp8 and functions in megagametogenesis and embryogenesis in plant.

Quantitative proteomics reveals key pathways in the symbiotic interface and the likely extracellular property of soybean symbiosome

An effective symbiosis between legumes and rhizobia relies largely on diverse proteins at the plantrhizobium interface for material transportation and signal transduction during symbiotic nitrogen fixation.Here,we report a comprehensive proteome atlas of the soybean symbiosome membrane(SM),peribacteroid space(PBS),and root microsomal fraction(RMF)using state-of-the-art label-free quantitative proteomic technology.In total,1759 soybean proteins with diverse functions are detected in the SM,and 1476 soybean proteins and 369 rhizobial proteins are detected in the PBS.The diversity of SM proteins detected suggests multiple origins of the SM.Quantitative comparative analysis highlights amino acid metabolism and nutrient uptake in the SM,indicative of the key pathways in nitrogen assimilation.The detection of soybean secretory proteins in the PBS and receptor-like kinases in the SM provides evidence for the likely extracellular property of the symbiosome and the potential signaling communication between both symbionts at the symbiotic interface.Our proteomic data provide clues for how some of the sophisticated regulation between soybean and rhizobium at the symbiotic interface is achieved,and suggest approaches for symbiosis engineering.

SPOROCYTELESS Is a Novel Embryophyte-Specific Transcription Repressor that Interacts with TPL and TCP Proteins in Arabidopsis

Germlines in plants are formed de novo during post-embryonic development, while little is known about the mechanism that controls this process. In Arabidopsis, the earliest gene controlling this process is SPOROCYTELESS （SPL）. A decade ago, we showed that loss of SPL function abolished sporogenesis in both male and female organs of Arabidopsis. However, its function is unclear up to now. In this study, we showed that SPL belongs to a novel transcription repressor family specific in embryophyte, which consists of 173 members in the land plants so far. All of them contain a conserved SPL-motif in their N-terminal and an ethylene-responsive element binding factor-associated amphiphilic repression （EAR） motif in the C-terminal, therefore designated as SPL-like, EAR-containing proteins （SPEARs）. Consis- tently, SPL acts as a transcriptional repressor in yeast and tobacco cells, and SPEAR proteins are able to form homodimer and/or het- erodimer with each other in vitro. Furthermore, SPEARs interact with the TOPLESS （TPL） co-repressors via the EAR motif and TCP family transcription factors in yeast cells. Together, we propose that SPL and SPEARs most likely belong to a novel transcription repressor family in land plants which may play a variety of developmental roles in plants.

Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development

Nucleolus is a membrane-less organelle where ribosomes are assembled, and ribosomal RNAs(r RNAs)transcribed and processed. The assembled ribosomes composed of ribosomal proteins and r RNAs synthesize proteins for cell survival. In plants, the loss of nucleolar ribosomal proteins often causes gametophytically or embryonically lethality. The amount of r RNAs are under stringent regulation according to demand and partially switched off by epigenetic modifications. However, the molecular mechanism for the selective activation or silencing is still unclear, and the transcriptional coordination of r RNAs and ribosomal proteins is also unknown. Here, we report the critical role of three Arabidopsis nucleolar proteins HDT1,HDT2, and HDT3 in fertility and transcription of r DNAs and r RNA processing-related genes through histone acetylation. This study highlights the important roles of transcriptional repression of ribosome biogenesisrelated genes for plant reproductive development.

Emerging role of ER quality control in plant cell signal perception

The endoplasmic reticulum quality control(ER-QC)is a conserved mechanism in surveillance of secreted signaling factors during cell-to-cell communication in eukaryotes.Recent data show that the ER-QC plays important roles in diverse cell-to-cell signaling processes during immune response,vegetative and reproductive development in plants.Pollen tube guidance is a precisely guided cell-cell communication process between the male and female gametophytes during plant reproduction.Recently,the female signal has been identified as small secreted peptides,but how the pollen tube responds to this signal is still unclear.In this review,we intend to summarize the role of ER-QC in plants and discuss the recent advances regarding our understanding of the mechanism of pollen tube response to the female signals.

SLOW WALKER3,Encoding a Putative DEAD-box RNA Helicase,is Essential for Female Gametogenesis in Arabidopsis

RNA helicases are adenosine tri-phosphatases that unwind the secondary structures of RNAs and are required in almost any aspect of RNA metabolism. They are highly conserved from prokaryotic to eukaryotic organisms. However, their precise roles in plant physiology and development remain to be clarified. Here we report that the mutation in the gene SLOW WALKER3 （SWA3） results in the slow and retarded progression of mitosis during megagametogenesis in Arabidopsis. SWA3 is a putative RNA helicase of the DEAD-box subfamily. Mutant megagametophyte development is arrested at fouror eight-nucleate stages, furthermore, one of the synergids in about half of the mutant embryo sacs displays abnormal polarity, with its nucleus locating at the chalazal end, instead of the micropylar end in the wild-type. Transmission of the mutation through female gametophytes is severely reduced in swa3. However, a small portion of mutant embryo sacs are able to develop into mature and functional female gametophytes when pollination was postponed. The SWA3 in Arabidopsis is a homolog of Dbp8 in yeast. Dbp8 interacts with Efs2 and is essential for biogenesis of 18S rRNA in yeast. Our data suggest that SWA3 may form a complex with AtEfs2 and take roles in ribosomal biogenesis as RNA helicase during megagametogenesis in Arabidopsis.

Pollen and Plant Reproduction Biology： Blooming from East to West

The idea of assembling a Special Issue on Pollen Tube and Reproduction in Molecular Plant was conceived during the organization of the 2012 Pollen Biology International Symposium and Workshop held at the Shanghai Institute of Plant Physiology and Ecology （SIPPE）, Chinese Academy of Science （CAS）, 27-31 October 2012. Wei-Hua Tang of the SIPPE led the organization, with the support of Hong-Wei Xue, Director of SIPPE acting as Chair of the Organization Committee. The 2-d symposium was attended by about 100 international participants and focused on reports and discus- sions on the most recent research activities in the field. The 2-d workshop that followed provided a forum for in-depth introduction on various aspects of pollen and plant reproduc- tion biology to about 200 graduate students, postdoctoral fellows, and new investigators to the field.

Novel Nuclear Protein ALC-INTERACTING PROTEIN1 is Expressed in Vascular and Mesocarp Cells in Arabidopsis

Pod shattering is an agronomical trait that is a result of the coordinated action of cell differentiation and separation. In Arabidopsis, pod shattering is controlled by a complex genetic network in which ALCATRAZ （ALC）, a member of the basic helix-loop-helix family, is critical for cell separation during fruit dehiscence. Herein, we report the identification of ALC-INTERACTING PROTEIN1 （ACI1） via the yeast two-hybrid screen. ACll encodes a nuclear protein with a lysine-rich domain and a C-terminal serine-rich domain. ACI1 is mainly expressed in the vascular system throughout the plant and mesocarp of the valve in siliques. Our data showed that ACI1 interacts strongly with the N-terminal portion of ALC in yeast cells and in plant cells in the nucleus as demonstrated by bimolecular fluorescence complementaUon assay. Both ACI1 and ALC share an overlapping expression pattern, suggesting that they likely function together in planta. However, no detectable phenotype was found in plants with reduced ACll expression by RNA interference technology, suggesting that ACll may be redundant. Taken together, these data indicate that ALC may interact with ACI1 and its homologs to control cell separation during fruit dehiscence in Arabidopsis.

Osmoregulation determines sperm cell geometry and integrity for double fertilization in flowering plants

Distinct from the motile flagellated sperm of animals and early land plants,the non-motile sperm cells of flowering plants are carried in the pollen grain to the female pistil.After pollination,a pair of sperm cells are delivered into the embryo sac by pollen tube growth and rupture.Unlike other walled plant cells with an equilibrium between internal turgor pressure and mechanical constraints of the cell walls,sperm cells wrapped inside the cytoplasm of a pollen vegetative cell have only thin and discontinuous cell walls.The sperm cells are uniquely ellipsoid in shape,although it is unclear how they maintain this shape within the pollen tubes and after release.In this study,we found that genetic disruption of three endomembrane-associated cation/H+exchangers specifically causes sperm cells to become spheroidal in hydrated pollens of Arabidopsis.Moreover,the released mutant sperm cells are vulnerable and rupture before double fertilization,leading to failed seed set,which can be partially rescued by depletion of the sperm-expressed vacuolar water channel.These results suggest a critical role of cell-autonomous osmoregulation in adjusting the sperm cell shape for successful double fertilization in flowering plants.

Erratum to“Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development”[Journal of Genetics and Genomics(2022)49,30–39]

This erratum clarifies information in the article“Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development”by Luo et al.(2021).In the section on“Phenotype of hdt mutants”,the T-DNA insertional knockdown mutant for HDT2(hdt2,salk_1247_A02)should be“Sail_1247_A02”in the main text and Fig.3A.

Patterning the embryo in higher plants:Emerging pathways and challenges

Embryogenesis,which establishes the basic body plan for the post-embryonic organs after stereotyped cell divisions,initiates the first step of the plant life cycle.Studies in the last two decades indicate that embryogenesis is a precisely controlled process,and any defect would result in abnormalities.Here we discuss the recent progresses,with a focus on the cellular pathways governing early embryogenesis in the model species Arabidopsis.

Transgenic Crops:An Option for Future Agriculture

The world population is projected to reach seven billion at the end of year 2011, with an increase of 1 billion from year 2000 to 2011. Currently, Asia alone accounts for about 60% of the world population. China and India together account for over 36%. It will be, undoubtedly, quite challenging to feed the increasing population of the world. On the other hand, the world＇s arable land will not increase and most likely it will reduce due to industrial development and urbanization in developing countries. On the other hand, global warming and climate changes,