Gibberellin (GA) is a plant hormone that regulates various physiological phenomena of plants. Studies on the dy mutant of rice indicated that GA_1 is the active form of GA that regulates shoot elongation. To confirm the importance of GA_1 , we successively cloned DY gene that encodes GA 3-oxidase, an enzyme that catalyzes the final step of GA_1 synthesis. Deletion of nine nucleotides that provided reduction in the enzyme activity was found in dy gene. Together with the previous studies on physiology and biochemistry of endogenous gibberellins in rice, we concluded that GA_1 is active per se for the shoot elongation of rice. Biological resources such as dwarf mutants played indispensable roles in the study. In 2001, RIKEN BioResource Center was established, and we started the collection, preservation and distribution of plant resources such as Arabidopsis seeds, plant cultured cells and genes. We have provided approximately 40,000 plant materials to more than 1,600 research groups and laboratories in the world. Reliability of the resource as well as observance of laws and rules is the most important in our resource project.

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Gibberellin (GA) regulates various developmental processes in plants. To study on some actions triggered by GA biochemically, we prepared antisera against GA. At first, we used the antisera for the detection of GA in plants. In developing seeds of morning glory and also of Arabidopsis, GA was immunologically detected in their integuments where starch granules were observed and then disappeared. Taking together with other result for related genes expression, we proposed that GA plays a role for seed maturation of dicotyledonous plants at least through the degradation of starch. Secondly, we established a biochemical method for a detection of water - soluble GA receptor candidates in crude solution, which led to the identification of a rice GA receptor, Gibberellin Insensitive Dwarf1 (GID1). Its GA - binding activity and ligand selectivity were confirmed. The suppressor of GA signaling called DELLA boosted the GA - binding activity of GID1 in vitro, which means the formation of a GID1-DELLA complex tightens the binding of GA to GID1. In Arabidopsis, we found three GA receptors. By using loss - of - function mutants, we elucidated the functional redundancy and partial specificity of their receptors. After some approaches, we proposed that the phenotype(s) appeared in the mutants depends on the abundance of the remaining receptor and on its preference to DELLAs.

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In higher plant, when wounding or grafting interrupted the original organ or tissue connection, cell division was induced and tissue-reunion occurs to restore physiological connections. Our previous work suggests that leaf gibberellin is required for the tissue-reunion of cortex in the cucumber and tomato cut hypocotyls. We identified the tissue reunion-responsive genes using Arabidopsis cut flowering stem. Genes that were up-regulated during the reunion process include those involved in cell division, cell wall modification, phytohormone-related gene and transcription factors (TFs). Among them, two plant-specific TF genes, ANAC071 and RAP2.6L, were abundantly expressed. ANAC071 was expressed at 1-3 days after cutting exclusively in the upper region of the cut gap with concomitant accumulation of indole-3-acetic acid. In contrast, RAP2.6L was expressed at 1 day after cutting exclusively in the lower region with concomitant deprivation of indole-3-acetic acid. The expression of ANAC071 and RAP2.6L were also promoted by ethylene and jasmonic acid, respectively. Our results suggested that plant-specific TFs differentially expressed around the cut position were essential for tissue reunion of Arabidopsis wounded flowering stems, and were under opposite control by polar - transported auxin, with modification by two wound-inducible hormones.

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Availability of mineral nutrients affects strigolactone (SL) production and exudation from plants. In legumes which form symbiotic relationship with root nodule bacteria, deficiency of phosphorus (P) but not other nutrients including nitrogen (N) significantly promoted SL production and exudation. By contrast, in non-legume plants, N deficiency as well as P deficiency increased SL exudation. Such a promotion of SL exudation under nutrient deficiency could be observed, in general, with mycotrophic plants but not with non-mycotrophic plants including Arabidopsis and white lupin.

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Endogenous peptide elicitors are 8-23 amino acid peptides that can induce plant defense responses including H_2O_2 generation, MAP kinase activation, and induction of defense related gene expression. These responses are very similar to those induced by pathogen-and herbivore-derived molecules called elicitors, which have recently been referred to as pathogen-associated molecular patterns (PAMPs) and herbivore-associated molecular patterns (HAMPs), respectively. Endogenous peptide elicitors are believed to be amplifiers of PAMP and HAMP to establish a strong defense response to combat pathogens and herbivores. Six different groups of endogenous peptide elicitors have been isolated thus far. In this review, we will summarize the characteristics of each peptide elicitor, the recently analyzed perception of AtPep by its receptors, and discuss the role of peptide elicitors in plant defense responses.

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Recent studies have identified small secretory peptides as intercellular signaling molecules in plant cell-cell communication. TDIF (tracheary element differentiation inhibitory factor) is a twelve amino-acid peptide originally isolated as an inhibitory factor for xylem cell differentiation in a xylogenic culture system of Zinnia elegans. TDIF is a CLE family peptide and is encoded by CLE41 and CLE44 genes in Arabidopsis thaliana. This finding led to the isolation of its membrane receptor, namely TDR, and a target transcription factor WOX4. Detailed analysis on their in planta functions showed that TDIF is a phloem-derived signal regulating the behavior of procambial stem cells localized between phloem and xylem tissues within the vasculature. In the procambial cells, the TDIF signal is perceived via the TDR receptor and plays two distinct functions : suppression of xylem differentiation and enhancement of proliferation. WOX4 function in TDIF signaling is limited to the latter function. I describe the detail of these works along with the studies on CLV3, a negative regulator for the shoot apical meristem stem cells, and some other CLE peptides acting on vascular development to point out the generality and diversity in molecular mechanisms and biological functions of CLE peptide signaling.

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Root meristem growth factor (RGF) is a 13-amino-acid tyrosine-sulfated peptide involved in maintenance of the root stem cell niche in Arabidopsis. RGF was identified in a search for sulfated peptides that recover root meristem defects of the tpst-1 mutant in combination with in silico screening of genes encoding sulfated peptides and practical bioassays using synthetic sulfated peptides. This approach is based on the assumption that the severe short root phenotype of the tpst-1 mutant reflects deficiencies in the biosynthesis of all the functional tyrosine-sulfated peptides. RGFs are produced from ≈ 100-amino-acid precursor peptides via post-translational sulfation and proteolytic processing. RGF family peptides are expressed mainly in the stem cell area and the innermost layer of central columella cells. RGF peptides regulate root development by upregulating PLETHORA transcription factor which are specifically expressed in root meristem and mediate patterning of the root stem cell niche.

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ROTUNDIFOLIA4 (ROT4) is a peptide unique to land plants. Angiosperm species have more than 10 paralogs (RTFL/DVLs) in their genome and the high redundancy is an obstacle to know the detailed function of this peptide family. The discovery of this peptide family was based on two indepdendent activation-tagging screenings in Arabidopsis thaliana for two different aims. First it was thought that the RTFL/DVL is involved in cell proliferative activity along the longitudinal axis of leaves because the over-expression of the members of RTFL/DVL causes stunted leaves. Our recent detailed analysis suggested that the ROT4 is involved in determination of longitudinal positional cues in lateral organs/tissues. Curiously, GFP-fused version of the ROT4 is localized on the plasma membrane, although the ROT4 itself has no special known motif. Here we overview the history of our understanding of the enigmatic RTFL/DVL family.

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Multicellular organisms achieve organ morphogenesis through coordination of cell proliferation and differentiation. Because plant cells do not migrate during organogenesis, cell-cell communications among various types of cells play important roles for elaboration of each organ morphology and also resultant final body shape. It has been known since 1950s that Arabidopsis erecta (er) mutants exhibit a characteristic compact inflorescence with short internodes and short pedicels. Because the ER gene encodes a receptor-like kinase, the identification of a ligand(s) for the receptor in the inflorescence regulation has been expected. Recently two members of the EPIDERMAL PATTERNING FAC-TOR-LIKE (EPFL) family encoding secreted cysteine-rich peptide hormones, EPFL4 and EPFL6, were identified as redundant ligand genes for the ER-mediated inflorescence growth. Interestingly, the endodermal expression of EPFL4 or EPFL6 and also the activity of ER in phloem are critical in the inflorescence regulation. These suggest that the inter-tissue layer communication between endodermis and phloem mediated by peptide hormones and a receptor coordinates inflorescence morphology. In this review, the detailed explanation of the EPFL4/6-ER signaling module and further prospects will be described.

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Pollen tube guidance is a crucial mechanism for successful fertilization in angiosperms, which precisely controls directional growth of pollen tubes of own species to deliver immotile sperm cells to an embryo sac. Since pollen tubes were observed to grow toward excised pistil tissues on a medium in the late nineteenth century, plant biologists have conducted studies to reveal mechanisms of pollen tube growth and guidance. Recently, pollen tube attractants, LURE peptides, have been identified in a unique dicot, Torenia fournieri. However, universal molecular mechanisms involving species-specific pollen tube attraction are still unclear. In this review, we present identification of pollen tube attractants of Arabidopsis thaliana, AtLURE1 peptides, and discuss universality, species specificity, and expression mechanism of the attractant molecules.

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Plant hormones regulate various aspects of the growth and development of plants. Perception and signaling of plant hormones are highly sophisticated, but have been increasingly clarified by biochemical and molecular techniques. Recently, chemical genetics is becoming a more powerful approach to elucidate hormone actions, where plant hormone agonists and antagonists as well as biosynthesis inhibitors are utilized. In this review, we give an overview of plant hormone agonists and antagonists which have been or can be used for elucidation of plant hormone actions. Some successful chemical genetic studies are also introduced.

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Determining the mobile signal used by plants to defend against biotic and abiotic stresses has proved elusive, but jasmonic acid (JA) and its derivatives appear to be involved. Using deuterium-labeled analogs, we investigated the systemic transport of jasmonoyl isoleucine (JA-Ile) in response to leaf wounding in tobacco (Nicotiana tabacum) and tomato (Solanum lycopersicum) plants. It was found that de novo synthesized JA-Ile responded to wound damages was transported to induce JA-mediated wound response in healthy systemic organ.

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