Anther dehiscence: Genetic and molecular characterization

Dehiscence is the terminal process in anther development that involves wall breakage to release pollen grains. Two anther cell-types, the septum and stomium cells located within the anther notch define the site of wall breakage. I utilized the tobacco anther for studies of cell development and the characterization of the dehiscence program, and the Arabidopsis anther as a genetic tool to identify mutants in dehiscence and anther structure. I carried out cell differentiation studies in both tobacco and Arabidopsis, and demonstrated when and where septum and stomium cells differentiate, and followed the degeneration of the septum and stomium which leads to the opening of the anther wall at dehiscence.;One of my major projects was screening Arabidopsis T-DNA and EMS mutagenized lines. The objective was to identify mutants defective in anther development. Two mutants, pollenless3 and delayed-dehiscence1 , were identified in which a T-DNA insertion enabled the isolation of the defective gene. pollenless3 was defective in male-meiosis and had anthers devoid of pollen grains. POLLENLESS3 transcripts were localized only in locule cells undergoing late stage meiosis. The POLLENLESS3 protein appeared to play a specific role in cell division events late in male-meiosis.;In delayed-dehiscence1, stomium cell degeneration was delayed and pollen grains were released too late for successful pollination. Characterization of the DELAYED-DEHISCENCE1 gene showed that it encoded an enzyme in the jasmonic acid biosynthesis pathway. The chemical complementation of the mutant phenotype with exogenous jasmonic acid, together with enzymatic studies, revealed that delayed-dehiscence1 was disrupted in the major pathway for jasmonic acid synthesis in Arabidopsis. These results demonstrated that jasmonic acid signaling plays a role in the timing of anther dehiscence at floral opening.;I utilized two Arabidopsis anther pattern mutants, aintegumenta and ettin, to test the hypothesis that the positioning of the septum and stomium was dependent upon the earlier establishment of the anther locules. The results suggested that the locules are responsible either directly or indirectly for transmitting a signal to the notch which is required for septum and stomium differentiation.;Taken together, these experiments indicate that the dehiscence process involves region-specific cell differentiation and degeneration events that are conserved in higher plants and that jasmonic acid plays a major role in anther dehiscence.