Chemical biology is a new research field to elucidate unknown mysteries in biology by compounds as research tools.　If we are able to find a novel compound that positively regulates plant growth, it will be useful tool, which can elucidate unknown molecular mechanisms in plant growth, and it will be used for applied plant science in agriculture.　Using these chemical biological approaches, I identified novel genes and compounds that regulated plant growth.　In the aspect of gene exploration, I had screened brassinosteroid （BR） signaling genes that promote plant growth.　At first, I had used brassinazole （Brz） that is synthesized as a specific inhibitor for BR biosynthesis enzyme DWF4.　Then, I attempted to screen for a mutant with a Brz-insensitive long hypocotyl phenotype using gain-of-function mutant germinations.　My first isolated mutant was named as bil1 （Brz-inseisitive-long hypocotyl1） and the resulted BIL1 is known as a master transcription factor that regulates 3,000 genes expressions.　Furthermore, I am continuing to screen and analysis of bil mutants, bss（Brz-sensitive-short hypocotyl）, bpg（Brz-insensitive-pale green）mutants.　Trials to reveal molecular mechanisms of plant growth based on novel BR signaling factors are still going on.

The phytohormone 7-iso-（+）-jasmonoyl-L-isoleucine （JA-Ile） mediates plant defense responses against environmental stresses such as herbivore and pathogen attacks.　JA-Ile induces protein-protein interaction （PPI） between COI1 （the F-box protein of E3 ubiquitin ligase） and JAZ （the transcriptional repressor proteins）, leading to plant defense responses, as well as plant growth inhibition or senescence.　COI1 and 13 subtypes of JAZ are encoded in the genome of Arabidopsis thaliana, and JA-Ile can induce PPI between COI1 and most of JAZ subtypes to cause various physiological responses at the same time.　However, the detailed function of most of JAZ subtypes remain unclear, partially due to the genetic redundancy of JAZ genes.　Here I summarize the studies of our versatile detection methods for COI1/JAZ PPI based on binary-tag pull-down or fluorescence anisotropy assay systems, according to the previously reported crystal structure of COI1/JAZ co-receptor.　By using these methods, a stereoisomer of （+）-coronatine （COR, a structural and biological mimic of JA-Ile） was found to be a moderate JAZ-subtype selective agonist.　Moreover, based on the stereoisomer of COR, rationally designed JAZ-subtype selective agonist （NOPh） that induces PPI between only two JAZ （subtype 9/10） and COI1 was reported.　It enhances defense responses against pathogen infection at concentrations that do not cause growth inhibition.　The unique bioactivity of NOPh can be attributed the uncoupling of the growth-defense trade-off through the selective activation of JAZ9-EIN3/EIL1-ORA59 signaling pathway.

It is an undeniable fact that herbivore attack is a major problem in agriculture.　As a result, a number of insecticides have been developed to support agricultural production.　In recent years, however, the emergence of the herbivores that developed highly insecticide resistance has become a global problem.　In particular, thrips have developed a high level of insecticide resistance in various parts of the world, and they have been rampant both in Japan and overseas.　In some areas, this is a serious situation leading to abandonment of cultivation.　Thysanoptera have a wide host range, causing damage to many crops and vegetables as well as flowers.　In addition, since these pest species are also vectors of plant viruses, they cause viral diseases such as tomato spotted wilt virus, chrysanthemum stem necrosis virus on crops, causing multiple damages. Moreover, since thrips are only about 1〜2 millimeters long, it is not easy to prevent them from invading large gardening facilities, such as plant factories, and once they do, the damage is devastating.　Because thrips can increase their population with females alone for parthenogenesis without males, invasion by only one female is a significant risk.　Thus, the development of new control measures against thrips has long been required, but a fundamental solution has yet to be reached.　Therefore, we have developed a repellent for the purpose of controlling thrips’ behavior based on the interaction between thrips and plants, rather than killing them, and are advancing research and development with the aim of developing innovative behavior control technology.

Plant growth and development is dynamically regulated by plant hormones.　Among them, auxins show unique directional transport designated polar auxin transport （PAT） by which auxin gradient is generated, it being instrumental in the diverse regulation of various plant developmental processes.　To clarify the mechanism by which gravity controls PAT, we carried out the space experiment “Auxin Transport” on the International Space Station （ISS） using etiolated pea and maize seedlings, focusing on auxin efflux carrier PIN proteins.　Here I would summarize the ISS experiment, and discuss the gravity-controlled mechanism to regulate PAT.　I also briefly introduce plant experiments done on the ISS.

Although water is essential for plant growth, excess water due to flooding has an adverse effect on the growth of most plants.　Rice, a semiaquatic species, has acquired specialized anatomical traits such as aerenchyma and radial oxygen loss barriers to survive under excess water conditions.　However, these traits are not effective under severe flooding such as continuous complete submergence.　Certain rice varieties have developed specific strategies to adapt to various flooding conditions such as complete submergence at germination, flash flooding, and periodic flooding, by regulating stem elongation and thereby plant height.　In this review, we describe here the recent progress on the molecular mechanisms regulating the anatomical traits and specific strategies to adapt to various flooded environments.　We primarily focus on our recent report describing the hormonal regulation of internode elongation in deepwater rice to adapt to periodic flooding.

Synthetic abscisic acid （ABA） agonists have distinct properties from naturally occurring one.　For instance, they have relatively simple structures, are not inactivated by ABA catabolic enzymes and can target specific receptor.　Therefore, synthetic ABA agonists are attractive tools for understanding molecular mechanism of ABA actions in plants.　Furthermore, ABA agonists will help crop productivity by optimizing ABA sensitivity.　The development of ABA agonist has been actively conducted since the identification of ABA receptor.　In addition, over 70 X-ray crystal structures of ABA receptors have been registered.　The accumulated information on the detailed structures of receptors and various ABA agonists make it possible to develop new molecules more accurately and rationally.　This research note introduces how we developed potent ABA agonist that exceeds the activity of natural ligand in Arabidopsis and wheat.

4-Methylthio-3-butenyl glucosinolate （glucoraphasatin） is known as the main glucosinolate of Japanese radish, daikon.　4-Methylthio-3-butenyl isothiocyanate （raphasatin） is also the main breakdown compound of glucoraphasatin by myrosinase.　Raphasatin is the starting compound of sulfurous odors and yellow pigments of manufacturing products of daikon.　Recently, three cultivars without containing glucoraphasatin, ‘Daikon parental line No.5’ for a breeding material, ‘Yuhaku’ and ‘Sarah White’ for the commercial cultivars were developed.　These cultivars were bred using lines lacking glucoraphasatin, which were successfully developed using mutants selected from genetic resources.　Currently, new manufacturing products from ‘Yuhaku’ or ‘Sarah White’ completely prevent sulfurous odors and yellow pigments.

Technology involving the targeted mutagenesis of plants using programmable nucleases has been developing rapidly and has enormous potential in next-generation plant breeding.　Its application has been hindered in many cases, however, due to technical hurdles, such as the low delivery rate of macromolecules into plant cells or tissues and difficulties in plant transformation and regeneration.　Here, we report a genome-editing system via PEG-Ca²⁺-mediated transfection of rice zygotes, produced by in vitro fertilization of isolated rice gametes.　Cas9-gRNA ribonucleoprotein complexes（RNPs）, were transfected into zygotes, resulting in the regeneration of plants with a high frequency of targeted mutations, in the range of 14-64%.　This novel and efficient plant genome-editing system has enormous potential for the improvement of rice, as well as other important crop species.

Biennial bearing of citrus is a major problem that must be resolved in the near future.　This problem mainly arises due to declining tree vigor and excessive flowering.　In satsuma mandarin （Citrus unshiu Marc.）, it was observed that application of 2.5 ppm gibberellic acid （GA） along with machine oil emulsion during the winters can suppress flowering in the following year.　The same effect is observed when the adjuvant is mixed with 2.5 ppm GA and is applied partially to the citrus trees.　Further, there are no adverse effects if urea is applied to restore the tree vigor.　However, for “Shiranuhi citrus cultivar,” spraying 2.5 ppm GA mixed with machine oil emulsion or adjuvant was found to be much more effective than GA-mixed with urea.　Therefore, plant growth regulators, such as GA, can be used at a lower concentration with penetrant adjuvant, to have the same effect as observed with the prevailing concentration.　Reduction in excess flowering can potentially prevent biennial bearing.　Moreover, using an adjuvant can lower plant growth regulator concentration and the cost.

It is customary to cultivate rice of tropical origin in the spring.　Here, I introduce a new technique, “Early-winter direct-sowing cultivation”, which sown seeds in the early winter of the previous year and overwinter in the soil for several months until the following spring.

Witchweed, the common name of Striga spp., is derived from their bewitching effects on their respective hosts.　When sorghum is planted in a Striga infested area, it grows normally but all of a sudden it stops growing, displays chlorosis and starts wilting.　To explain this puzzling behavior farmers in East Africa, where Striga has its center of origin, thought that the crop has been bewitched.　The term bewitch is a verb and so has nothing to do with gender.　However, beautiful flowers of Striga remind us of ladies.　Recently it was elucidated that the witchcraft performed by Striga is due, at least in part, to abscisic acid （ABA）.　Striga seeds, in response to root exudates, germinate and the seedlings produce and secrete ABA, which impairs host growth.　Beside recognition of host-derived signals, insensitivity of stomatal behavior to ABA, secretion of ABA by seedlings and their plausible roles in sustenance of the parasitic life of Striga remain fascinating mysteries.