Anther Dehiscence Is Regulated By Gibberellic Acid In Yellow Lupine (Lupinus Luteus L.)

Abstract

Background:Anther dehiscence resulting in the release of pollen grains is tightly regulated in spatio-temporal manner by various factors. In yellow lupine (Lupinus luteus L.), the species which shows cleistogamy, the anthers split before the flowers open but the course and regulation of this process is unknown. Specific control of the anther development takes place with the participation of hormonal pathways, the wide action of which ensures reproductive success. In our previous research we have shown that the lowest transcript level of LlDELLA1, a main repressor of gibberellin (GA) signaling, in flower and early pod development occurs about the time of anther opening; therefore the main purpose of this study was to precisely investigate the gibberellic acid (GA3)-dependent regulation of anther dehiscence program in yellow lupine.Results:In this paper we showed the specific changes in the yellow lupine anther structure during the dehiscence and identified several genes widely-associated with this process, including deposition of lignocellulosic secondary thickening in the endothecium, enzymatic breakdown of cell walls at the septum/stomium and cell degeneration via programmed cell death (PCD). The expression profile of genes varied over time with the most intense mRNA accumulation in the phases prior to or about time of anther opening. The transcriptional activity revealed also that these genes are highly co-expressed and regulated in a GA-dependent manner. The cellular and tissue localization of GA3 exhibited that these molecules are present right before anther opening, mainly in septum cells, near the vascular bundle and in the endothecium, and later they were completely undetectable. The GA3 localization strongly correlates with the transcriptional activity of genes related with GA biosynthesis and deactivation. The obtained results also suggest that GA3 controls LlGAMYB expression via LlMIR159-dependent pathway.Conclusions:The presented results show a clear contribution of GA3 in the control of the extensive anther dehiscence program in yellow lupine. Understanding the processes underlying pollen release at hormonal and molecular level is a significant aspect in controlling fertility in economically important legume crop species and increased attention of breeders.