Arabidopsis CAMs and CMLs: Regulation and functions of genes encoding potential calcium sensors
Doctor of Philosophy
The 57-member family of calmodulin (CaM) and CaM-Like (CML) proteins of Arabidopsis, defined and characterized in this thesis, have a strong potential to serve as sensors and interpreters of calcium signals, which are used in plants to convey information about and elicit specific responses to biotic and abiotic stimuli. Despite this opportunity to affect diverse aspects of plant biology, gene expression patterns or physiological function have been only marginally described for less than 30% of this family. The subset of genes characterized here serve as a primer to a comprehensive analysis of CAM and CML gene expression and function. To examine gene expression, mRNA levels were directly measured for 13 genes using northern analysis or quantitative-PCR (Q-PCR). The CAMs and CMLs tested show distinct, but sometimes overlapping, expression patterns both in induction of expression by stimuli and in localization throughout the plant. Indirect gene expression detection using GUS reporter transgenics allows more precise localization of expression for 15 CAMs and CMLs. Additionally, subcellular fractionation shows that CML12/TCH3 protein may be associated with multiple membranes. Physiological functions of the CAMs and CMLs can be elucidated by analysis of mutants expected to lack CaM or CML proteins. From this work, 50 cam or cml mutants were identified. Mutants chosen for in-depth study, cml11 and cml12/tch3, are among the first described mutations in an Arabidopsis CAM or CML. Root border cells accumulate in cml11, and this difference may contribute to root penetration of media. Although CaM and CML proteins share between 16 and 100 percent identity, it is likely that they have independent functions. CAMs and CMLs show non-redundant spatiotemporal patterns of gene expression, indicating that their proteins may function at different times or locations. Understanding gene expression regulation and physiological function for each CAM and CML will help us understand one aspect of how plants decode calcium signals necessary to complete specific developmental processes or survive changing environmental conditions.
Genetics; Plant physiology