Our study gives an opportunity to understand dormancy maintenance and breaking mechanisms.
A crucial and unanswered question is how constitutive RGL2 expression is achieved in dormant seeds. Constitutive RGL2 accumulation in dormant seeds may result from higher RGL2 protein stability or higher RGL2 specific activity to promote ABA synthesis, which in turn promotes higher RGL2 mRNA levels. The first possibility can be addressed following a HA-RGL2 protein half-life in seeds of dormant and non-dormant transgenic wild type plants (CVI or C24 ecotypes which show high levels of dormancy) expressing HA-RGL2 after translation inhibition. The half-life of RGL2 protein can be also measured in a cell-free assay. RGL2 protein (from wild type seeds, from HA-RGL2 transgenic lines or recombinant RGL2) degradation can be monitored by Western blot in extracts from dormant and non-dormant seeds in the presence or absence of GA.
Our results showed that dormant wild type seeds fail to up-regulate SLY1 mRNA accumulation upon seed imbibition, unlike non-dormant seeds. Thus, we hypothesize that constitutive RGL2 accumulation in dormant seeds might result from low expression of an important component of the DELLA degradation machinery. To check this hypothesis HA-SLY1 over-expression lines can be generated in highly dormant ecotypes (such as CVI). One could expect that forced HA-SLY1 expression to the level of non-dormant seeds will break dormancy and trigger dormant seed germination. Green Fluorescent Protein (GFP) DNA sequences fused to SLY1 promoter sequences may be introduced and expressed in the dormant CVI ecotype.
Mutagenesis of such transgenic lines and screening for plants that fail to up-regulate promSLY1::GFP after stratification may lead to the discovery of factors important for dormancy alleviation. Moreover, a careful analysis of SLY1 and RGL2 expression in various mutants shown to be affected in dormancy maintenance (dog1, hub1) may elucidate a role of positive regulators of seed dormancy reported so far.
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