Anther dehiscence is regulated by gibberellic acid in yellow lupine (Lupinus luteus L.)

BackgroundAnther dehiscence resulting in the release of pollen grains is tightly regulated in a spatiotemporal manner by various factors. In yellow lupine (Lupinus luteus L.), a species that shows cleistogamy, the anthers split before the flowers open, but the course and regulation of this process are unknown. The specific control of anther development takes place via hormonal pathways, the wide action of which ensures reproductive success. In our previous research concerning flower and early pod development in yellow lupine, we showed that the lowest transcript level of LlDELLA1, a main repressor of gibberellin (GA) signalling, occurs approximately at the time of anther opening; therefore, the main purpose of this study was to precisely investigate the gibberellic acid (GA(3))-dependent regulation of the anther dehiscence in this species.ResultsIn this paper, we showed the specific changes in the yellow lupine anther structure during dehiscence, including secondary thickening in the endothecium by lignocellulosic deposition, enzymatic cell wall breakdown at the septum/stomium and cell degeneration via programmed cell death (PCD), and identified several genes widely associated with this process. The expression profile of genes varied over time, with the most intense mRNA accumulation in the phases prior to or at the time of anther opening. The transcriptional activity also revealed that these genes are highly coexpressed and regulated in a GA-dependent manner. The cellular and tissue localization of GA(3) showed that these molecules are present before anther opening, mainly in septum cells, near the vascular bundle and in the endothecium, and that they are subsequently undetectable. GA(3) localization strongly correlates with the transcriptional activity of genes related to GA biosynthesis and deactivation. The results also suggest that GA(3) controls LlGAMYB expression via an LlMIR159-dependent pathway.ConclusionsThe presented results show a clear contribution of GA(3) in the control of the extensive anther dehiscence process in yellow lupine. Understanding the processes underlying pollen release at the hormonal and molecular levels is a significant aspect of controlling fertility in this economically important legume crop species and is of increasing interest to breeders.

Automated summary

This study demonstrated the specific changes in the yellow lupine anther structure during dehiscence, and identified genes associated with this process, showing that their transcription is highly coexpressed and regulated in a GA-dependent manner. The localization of GA(3) in septum cells, near the vascular bundle, and endothecium before anther opening suggests its role in regulating gene expression related to GA biosynthesis and deactivation. The results provide valuable insights into the hormonal and molecular regulation of anther dehiscence in yellow lupine, offering potential applications in breeding for improved fertility in this economically important crop species.