Regulation of Plant Growth & Development

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To investigate the important agricultural characters of barley "uzu" and "sprouting", the molecular analysis was performed. The semi-dwarf characteristic leading to lodging resistance is very important for high yields. Semi-dwarf barley accessions carrying the "uzu" gene, called "uzu" barley in Japan, are non-responding to brassinolide and accumulate brassinosteroids (BRs). We cloned the barley homolog of the BR-receptor gene, HvBRI1, a candidate for the uzu gene suggested by the marker synteny of rice and barley chromosomes. The comparison of HvBRI1 sequences in uzu and normal lines demonstrated that the uzu phenotype is correlated with a missense mutation in the HvBRI1 gene. Pre-harvest sprouting of cereal grain damages the quality of the end product. To investigate whether the regulation of abscisic acid (ABA) content is related to germinability during grain development under field conditions, cDNAs for key ABA biosynthetic and catabolic enzymes (9-cis-epoxycarotenoid dioxygenase and ABA 8'-hydroxylase) were cloned from barley. Expression and ABA-quantification analysis demonstrated that the change in the ABA content of imbibing grains following dormancy release is likely to reflect changes in the expression patterns of these genes. The varied expression levels of these genes, which would have effects on the activity of ABA biosynthesis and catabolism, might be reflected in the germinability of field-grown barley.

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Chloroplast differentiation was tightly related with photomorphogenesis that based on hypocotyls elongation and cotyledon opening. At first, to analysis mechanism of chloroplast differentiation, we cloned two regulator of chloroplast genome, CND41 and PTF1. At the second, we identified that brassinosteroid deficiency in the dark with Brz, brassinosteroid biosynthesis inhibitor, caused not only the deetiolation but also the acceleration to chloroplast from etioplast after the short-term-light treatment to cotyledon that germinated in the dark with Brz. Many chloroplast genes that were encoded on the both of nuclei and plastid genome were expressed in the dark with Brz higher than the control plant without Brz. In order to analyze in detail the mechanisms of brassinosteroid signal transduction, we screened for mutants that showed longer hypocotyls than wild type when grown with Brz in the dark, and designated bil mutants (Brz-insensitive-long hypocotyl). We identified a dominant mutant bill that encoded on a novel bHLH trans-acting factor that stability was regulated by a kinase and proteasome system.

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Cytochrome P450 monoxygenases (P450s) are heme-containing membrane proteins and catalyze the monooxygenation reactions in a wide range of metabolic pathways of various bioactive substances. In this study, several plant P450s belonging to 85-clan and 710-clan were investigated by biochemical approaches. (1) CYP707As have been identified as a major ABA catabolic enzyme, ABA 8'-hydroxylase. A triazole-type growth retardant, uniconazole-P, was found to be a potent inhibitor of ABA 8'-hydroxylase, and the inhibitor treated plants showed enhanced drought tolerance because of ABA accumulation. (2) Enzymatic functions of CYP90A1, 90B1, 90C1, 90D1, and 724B1 involved in BR biosynthesis were clarified by using an in vitro assay reconstituted with the recombinant P450s expressed either in a baculovirus-insect cell system or in a bacterial-expression system, and these studies revealed that BRs are biosynthesized via the campestanol-independent pathway. (3) CYP710As were found to encode plant sterol C-22 desaturases. Arabidopsis CYP710A1/A3/A4 catalyze C-22 desaturation of β-sitosterol to produce stigmasterol, while CYP710A2 specifically C-22 desaturate 24-epi-campesterol to produce brassicasterol, which is a unique sterol in Brassica species.

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The root parasitic weeds Striga spp., present severe biological constraints to agriculture in low-input farming systems in the African savanna. Species of economic importance are S. asiatica (L.) kuntze and S. hermonthica (Del.) Benth., on cereals, and S. gesnerioides (Willd.) Vatke on cowpea [Vigna unguiculata (L.) Walp]. Recent surveys indicated that the parasite is spreading rapidly. At present the infested area is estimated to be 7.4 million hectares. The Striga problem, a part from the invasive nature of the parasite, is an outcome of demographic, socioeconomic, ethnic and environmental variables. Prodigious seed production and prolonged viability of seeds make Striga a difficult to control weed. The irrevocable damage Striga inflects on its host, prior to emergence, makes control of the parasite by post-emergence treatments less captivating to farmers. Available control practices, including cultural, chemical, biological and resistant varieties, are only partially effective. In Africa the solution should be simple, easy to implement, sustainable, durable and inexpensive. An integrated management strategy with tolerant and/or resistant crop cultivars in rotation with non host crops, as a pivotal component, is imperative.

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