GAMYB controls different sets of genes and is differentially regulated by microRNA in aleurone cells and anthers

GAMYB is a component of gibberellin (GA) signaling in cereal aleurone cells, and has an important role in flower development. However, it is unclear how GAMYB function is regulated. We examined the involvement of a microRNA, miR159, in the regulation of GAMYB expression in cereal aleurone cells and flower development. In aleurone cells, no miR159 expression was observed with or without GA treatment, suggesting that miR159 is not involved in the regulation of GAMYB and GAMYB-like genes in this tissue. miR159 was expressed in tissues other than aleurone, and miR159 over-expressors showed similar but more severe phenotypes than the gamyb mutant. GAMYB and GAMYB-like genes are co-expressed with miR159 in anthers, and the mRNA levels for GAMYB and GAMYB-like genes are negatively correlated with miR159 levels during anther development. Thus, OsGAMYB and OsGAMYB-like genes are regulated by miR159 in flowers. A microarray analysis revealed that OsGAMYB and its upstream regulator SLR1 are involved in the regulation of almost all GA-mediated gene expression in rice aleurone cells. Moreover, different sets of genes are regulated by GAMYB in aleurone cells and anthers. GAMYB binds directly to promoter regions of its target genes in anthers as well as aleurone cells. Based on these observations, we suggest that the regulation of GAMYB expression and GAMYB function are different in aleurone cells and flowers in rice.     

Regulation and interaction of multiple protein factors with the proximal promoter regions of a rice high pl α-amylase gene

Summary The -amylase gene is known to be regulated by the plant hormone gibberellin (GA) in cereal aleurone cells. The accumulation of the mRNA corresponding to a rice high pl -amylase gene, OSamy-c, was stimulated 20-fold by exogenous GA, in half-seeds lacking embryos. Regulatory regions in the promoter of this high pl subfamily were analyzed. The OSamy-c 5 flanking sequence, spanning positions — 231 to + 29, was fused upstream of the -glucuronidase (GUS) gene coding region. The delivery of this plasmid into rice aleurone cells by the biolistic method resulted in a GA-stimulated synthesis of GUS. Gel retardation assays were performed to study protein-DNA interactions between putative regulatory sequences of OSamy-c and partially purified rice seed extracts. We identified multiple seed-specific protein factors that bind to proximal regions of the OSamy-c promoter between positions — 231 and — 162. Five different proteins were distinguished based on competitive binding studies. Three protein binding regions were located by footprinting analyses, one of which is located in the conserved sequence also found upstream of other GA-inducible genes. Two protein factors in rice aleurone cells that interact with the putative regulatory sequence do not require GA induction.     

GA调节禾谷类a-淀粉酶基因表达的信号转导及分子机制

用GAs处理禾谷类糊粉细胞原生质体后,可以诱导α_淀粉酶的合成与分泌。ABA抑制GAs的诱导作用并可刺激ABA诱导蛋白的产生。GAs和ABA的受体位于质膜上。最近的研究表明：G蛋白、cGMP、Ca2+和钙调素、三磷酸肌醇（IP3）及蛋白质磷酸酶（PP1和PP2A）都不同程度的参与了GA响应的信号传导过程。已克隆出一些可在转录水平上调节GA诱导基因的顺反子,并证明它们在禾谷类糊粉细胞中的GA响应事件中起至关重要的作用。有证据表明GA在α 淀粉酶的转录后水平的调节上也有作用。     

Phytohormone-regulated β-amylase gene expression in rice

The expression of -amylase genes in rice (Oryza sativa) and its regulation by phytohormones gibberellic acid (GA) and abscisic acid (ABA) were examined. Upon germination -amylase is synthesizedde novo in aleurone cells and (GA) is not required. Exogenous addition of GA does not enhance the -amylase activity, while ABA inhibits the -amylase activity, mRNA accumulation, and the germination of rice seeds. GA can reverse ABA inhibition of -amylase expression, but not ABA inhibition of seed germination. Such regulation represents a new interaction of ABA and GA.     

The promoter of the asi gene directs expression in the maternal tissues of the seed in transgenic barley

The bifunctional -amylase/subtilisin inhibitor (BASI) is an abundant protein in barley seeds, proposed to play multiple and apparently diverse roles in regulation of starch hydrolysis and in seed defence against pathogens. In the Triticeae, the protein has evolved the ability to specifically inhibit the main group of -amylases expressed during germination of barley and encoded by the amy1 gene family found only in the Triticeae. The expression of the asi gene that encodes BASI has been reported to be controlled by the hormones abscisic acid (ABA) and gibberellic acid (GA). Despite many studies at the gene and protein level, the function of this gene in the plant remains unclear. In this study, the 5-flanking region (1033 bp, 1033-asi promoter) and the 3-flanking region (655 bp) of the asi gene were isolated and characterised. The 1033-asi promoter sequence showed homology to a number of ciselements that play a role in ABA and GA regulated expression of other genes. With a green fluorescent protein gene (gfp) as reporter, the 1033-asi promoter was studied for spatial, temporal and hormonal control of gene expression. The 1033-asi promoter and its deletions direct transient gfp expression in the pericarp and at low levels in mature aleurone cells, and this expression is not regulated by ABA or GA. In transgenic barley plants, the 1033-asi promoter directed tissue-specific expression of the gfp gene in developing grain and germinating grain but not in roots or leaves. In developing grain, expression of gfp was observed specifically in the pericarp, the vascular tissue, the nucellar projection cells and the endosperm transfer cells and the hormones ABA or GA did not regulate this expression. In mature germinating grain gfp expression was observed in the embryo but not in aleurone or starchy endosperm. However, GA induced gfp expression in the aleurone of mature imbibed seeds from which the embryo had been removed. Expression in maternal rather than endosperm tissues of the grain suggests that earlier widespread assumptions that the protein is expressed largely in the endosperm may have been largely based on analysis of mixed grain tissues. This novel pattern of expression suggests that both activities of the protein may be primarily involved in seed defence in the peripheral tissues of the seed.