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.     

The rice FON1 gene controls vegetative and reproductive development by regulating shoot apical meristem size

Most plant organs develop from meristems. Rice FON1, which is an ortholog of Clv1, regulates stem cell proliferation and organ initiation. The point muta-tions, fon1-1 and fon1-2, disrupt meristem balance, resulting in alteration of floral organ numbers and the architecture of primary rachis branches. In this study, we identified two knockout alleles, fon1-3 and fon1-4, generated by T-DNA and Tos17 insertion, respectively. Unlike the previously isolated point mutants, the null mutants have alterations not only of the reproductive organs but also of vegetative tissues, producing fewer tillers and secondary rachis branches. The mutant plants are semi-dwarfs due to delayed leaf emergence, and leaf senescence is delayed. SEM analysis showed that the shoot apical meristems of fon1-3 mutants are enlarged. These results indicate that FON1 controls vegetative as well as reproductive development by regulating meristem size.     

The Role of GAMYB Transcription Factors in GA-Regulated Gene Expression

A gibberellin- and abscisic acid-regulated MYB, GAMYB, was first identified as an activator of GA-regulated genes in cereal aleurone. Here we review recent advances made in delineating the signaling events related to GAMYB expression and function in aleurone. In addition, there is a growing body of evidence that GAMYB plays an important role in other aspects of plant growth and development, including anther development, stem elongation, floral initiation and seed development.     

α-Amylase production is induced by sulfuric acid in rice aleurone cells

The hydrolytic enzyme alpha-amylase (EC 3.2.1.1) is produced mainly in aleurone cells of germinating cereals, and the phytohormone gibberellin (GA) is essential for its induction. However, in rice (Oryza sativa L.), sulfuric acid (H(2)SO(4)) induces alpha-amylase production in aleurone tissue even in the absence of GA. Here, the pre-treatment of rice aleurone cells with H(2)SO(4) and incubation in water induced alpha-amylase activity, as if the cells had been incubated in GA solution.     

水稻叶绿素a氧化酶基因突变体的鉴定及其对氮营养的响应

对从日本获得的水稻Tos17插入突变基因进行了鉴定,并通过PCR技术对其插入位点和纯合体进行了分析和筛选。结果表明,Tos17插入在序列号为DP000086的基因,在此基因反向互补序列的1579bp处,在mRNA序列的第5个外显子区域,是水稻的一个叶绿素a氧化酶基因,而且此基因在单一的铵营养下表达减弱,氮饥饿条件下表达增强。利用Tos17未端和插入位点上下游设计引物进行PCR反应,鉴定到3株纯合突变体株,为进一步研究其功能奠定了基础。     

Isolation and characterization of rice phytochrome A mutants

To elucidate phytochrome A (phyA) function in rice, we screened a large population of retrotransposon (Tos17) insertional mutants by polymerase chain reaction and isolated three independent phyA mutant lines. Sequencing of the Tos17 insertion sites confirmed that the Tos17s interrupted exons of PHYA genes in these mutant lines. Moreover, the phyA polypeptides were not immunochemically detectable in these phyA mutants. The seedlings of phyA mutants grown in continuous far-red light showed essentially the same phenotype as dark-grown seedlings, indicating the insensitivity of phyA mutants to far-red light. The etiolated seedlings of phyA mutants also were insensitive to a pulse of far-red light or very low fluence red light. In contrast, phyA mutants were morphologically indistinguishable from wild type under continuous red light. Therefore, rice phyA controls photomorphogenesis in two distinct modes of photoperception--far-red light-dependent high irradiance response and very low fluence response--and such function seems to be unique and restricted to the deetiolation process. Interestingly, continuous far-red light induced the expression of CAB and RBCS genes in rice phyA seedlings, suggesting the existence of a photoreceptor(s) other than phyA that can perceive continuous far-red light in the etiolated seedlings.     

Isolation and identification of glycosylphosphatidylinositol-anchored arabinogalactan proteins and novel beta-glucosyl Yariv-reactive proteins from seeds of rice (Oryza sativa)

Arabinogalactan proteins (AGPs) are highly glycosylated extracellular glycoproteins playing important roles in plant growth and development. We have previously reported the possibility that AGPs are involved in the induction of alpha-amylase by gibberellin (GA) in barley aleurone layers by using the beta-glucosyl Yariv reagent (beta-GlcY), which has been presumed to specifically bind AGPs. In this present study, we isolated beta-GlcY-reactive proteins from rice bran rich in aleurone cells. The N-terminal sequences of classical AGP and AG peptides were determined from hydrophilic fractions obtained by reversed phase HPLC. Interestingly, a novel non-specific lipid transfer protein-like protein (OsLTPL1) and a novel early nodulin-like protein (OsENODL1) were also identified in the more hydrophobic fractions from HPLC as beta-GlcY-reactive proteins. Expression analysis of the genes coding for these proteins was performed. While classical AGP, AG peptides and OsLTPL1 were expressed in various parts of rice, OsENODL1 showed temporally and spatially specific expression in the aleurone layers. This new beta-GlcY-reactive protein is a promising candidate for the extracellular signaling factors of GA action in cereal seeds. Furthermore, the possibility that proteins with the AG glycomodule might react with beta-GlcY may broaden the definition of AGPs.