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.     

cGMP Is Required for Gibberellic Acid-Induced Gene Expression in Barley Aleurone

The occurrence and roles of cGMP were investigated in aleurone layers and protoplasts isolated from barley (cv Himalaya) grain. Levels of cGMP in freshly isolated barley aleurone layers ranged from 0.065 to 0.08 pmol/g fresh weight of tissue, and cGMP levels increased transiently after incubation in gibberellic acid (GA). Abscisic acid (ABA) did not increase cGMP levels in aleurone layers. LY 83583 (LY), an inhibitor of guanylyl cyclase, prevented the GA-induced increase in cGMP and inhibited GA-induced [alpha]-amylase synthesis and secretion. The inhibitory effects of LY could be overcome by membrane-permeant analogs of cGMP. LY also prevented GA-induced accumulation of [alpha]-amylase and GAMYB mRNAs. cGMP alone was not sufficient to induce the accumulation of [alpha]-amylase or GAMYB mRNA. LY had a less dramatic effect on the accumulation of mRNAs encoding the ABA-responsive gene Rab21. We conclude that cGMP plays an important role in GA, but not ABA, signaling in the barley aleurone cell.     

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.     

Gibberellin-mediated proteasome-dependent degradation of the barley DELLA protein SLN1 repressor

DELLA proteins are nuclear repressors of plant gibberellin (GA) responses. Here, we investigate the properties of SLN1, a DELLA protein from barley that is destabilized by GA treatment. Using specific inhibitors of proteasome function, we show that proteasome-mediated protein degradation is necessary for GA-mediated destabilization of SLN1. We also show that GA responses, such as the aleurone alpha-amylase response and seedling leaf extension growth, require proteasome-dependent GA-mediated SLN1 destabilization. In further experiments with protein kinase and protein phosphatase inhibitors, we identify two additional signaling steps that are necessary for GA response and for GA-mediated destabilization of SLN1. Thus, GA signaling involves protein phosphorylation and dephosphorylation steps and promotes the derepression of GA responses via proteasome-dependent destabilization of DELLA repressors.     

Some histochemical features of anther wall of <Emphasis Type="Italic">Leucojum aestivum</Emphasis> (Amaryllidaceae) during pollen development

In this study, polysaccharide and RNA contents of anthers were investigated on different phases of sporogenesis by using light microscopy techniques from histological and cytological point of view in Leucojum aestivum. Paraffin and semi-thin sections of anthers were stained with toluidine blue and PAS. Anthers were tetrasporangiate. The wall of the anther consists of an epidermis, endothecium, middle layer and glandular tapetum. During one nucleated microspore and mature pollen phase microspores and tapetum cells began to degenerate and they were become very rich of RNA in L. aestivum. And also RNA content was increased in endothecium and middle layer cells except the epidermis cells of anther wall. An increase in RNA content indicates cell activation. Polysaccharides were not seen in young anther wall but they were seen in older ones. They were generally condensed in the cell walls and especially in the cell walls of vascular bundles of connective tissue. This could be thought that insoluble polysaccharides were used in metabolic events in early developmental stages. Appearance of polysaccharides in late phases was indicated that polysaccharides were used in the formation of cuticule and differentiation of endothelium cell walls.