ROLE OF A GATA-TYPE ZINC FINGER PROTEIN IN REGULATING SEED DORMANCY IN ARABIDOPSIS THALIANA

Abstract

Seed germination is under the tight control of phytohormones, gibberellic acid (GA) and abscisic acid (ABA), the levels of which determine the switch from dormancy to germination under favourable environmental conditions. One of the key transcriptional repressors of GA signalling in seed germination is the DELLA protein, RGA-Like 2 (RGL2). However, the molecular mechanism of repression downstream of RGL2 is unknown. Based on an earlier microarray analysis done in our laboratory, we identified a gene-encoding a GATA-type zinc finger transcription factor (GATA12) as one of the downstream targets of RGL2 protein. Using chromatin immunoprecipitation studies, we showed that a protein complex containing RGL2 can bind to the promoter of GATA12 and thereby regulate the gene. We found that freshly harvested unstratified seeds of GATA12 antisense suppression lines have reduced dormancy than WT, while over-expression lines show enhanced dormancy. Our data show that GATA12 transcripts are negatively regulated by GA. Suppression of GATA12 increases the sensitivity of the GA biosynthetic mutant (ga1) seeds to exogenous GA application. Also, GATA12 transcript levels reduce dramatically under dormancy-breaking conditions like dry storage and cold stratification of seeds. Our findings have contributed more to our knowledge of gibberellin signalling downstream of RGL2 and thus have shed more light on the mechanism of dormancy release and seed germination. On a global perspective, this knowledge will help to device strategies to overcome problems of pre-harvest sprouting and asynchronous germination in agriculture.