CALCIUM/CALMODULIN-BINDING PROTEINS AND THEIR ROLE IN REPRODUCTIVE DEVELOPMENT AND STRESS RESPONSES IN PLANTS

JING XI

It has been well documented that calcium/calmodulin signaling plays important roles in plant growth, development and responses to environmental stimuli. In recent years, a variety of calcium/calmodulin-binding proteins with unique regulatory controls have been identified that play critical roles in these signaling pathways. Herein, for the first time two plant calcium/calmodulin-binding transcription factors, GT2-like protein (AtGT2L) and Arabidopsis thaliana signal responsive 1 protein (AtSR1), are revealed to be critical in reproductive development and herbivore-induced wound response, respectively. AtGT2L is predicted to belong to a plant-specific family of GT-2 like trihelix transcription factors. In this investigation, biochemical approaches confirm that AtGT2L is a calcium/calmodulin-binding protein with DNA-binding activity as well as transcriptional activation ability. Functional analysis of AtGT2L in Arabidopsis demonstrates that overexpression of AtGT2L in the wild-type plants leads to pleiotropic phenotypes including dwarfism, curly leaves and male sterility, suggesting that AtGT2L is involved in leaf morphogenesis and reproductive development. However, plants overexpressing a mutant AtGT2L protein with impaired calmodulin-binding ability failed to show similar phenotypes. These results demonstrate that calcium/calmodulin-binding is required for AtGT2L to regulate plant morphogenesis and fertility. It has been reported that AtSRs (also known as AtCAMTAs) can respond differentially to wounding stress and AtSR1/CAMTA3 is a negative regulator of salicylic acid-mediated plant innate immunity. This investigation documents that atsr1 null mutants are more susceptible to herbivore attack than wild-type plants. Furthermore, complementation of the atsr1 null mutant by overexpressing wild-type AtSR1 protein, but not mutated AtSR1 with impaired calmodulin-binding ability, can effectively restore plant resistance to herbivore attack, indicating that calcium/calmodulin-binding is also critical for AtSR1-mediated herbivore-induced wound response. In addition, it is observed that elevated salicylic acid level in atsr1 null mutants has a negative impact on both basal and induced biosynthesis of jasmonates. Taken together, these results reveal that calcium/calmodulin-mediated signaling regulates plant response to herbivore attack/wounding by modulating salicylic acid-jasmonate crosstalk through AtSR1.

CALCIUM/CALMODULIN-BINDING PROTEINS AND THEIR ROLE IN REPRODUCTIVE DEVELOPMENT AND STRESS RESPONSES IN PLANTS

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