Molecular and Genetic Evidence for the Key Role of AtCaM3 in Heat-Shock Signal Transduction in Arabidopsis    

Abstract

Heat shock (HS) is a common form of stress suffered by plants. It has been proposed that calmodulin (CaM) is involved in HS signal transduction, but direct evidence has been lacking. To investigate the potential regulatory function of CaM in the HS signal transduction pathway, T-DNA knockout mutants for AtCaM2, AtCaM3, and AtCaM4 were obtained and their thermotolerance tested. Of the three knockout mutant plants, there were no differences compared with wild-type plants under normal conditions. However, the AtCaM3 knockout mutant showed a clear reduction in thermotolerance after heat treatment at 45°C for 50 min. Overexpression of AtCaM3 in either the AtCaM3 knockout or wild-type background significantly rescued or increased the thermotolerance, respectively. Results from electrophoretic mobility-shift assays, real-time quantitative reverse transcription-polymerase chain reaction, and western-blot analyses revealed that, after HS, the DNA-binding activity of HS transcription factors, mRNA transcription of HS protein genes, and accumulation of HS protein were downregulated in the AtCaM3 knockout mutant and up-regulated in the AtCaM3-overexpressing transgenic lines. Taken together, these results suggest that endogenous AtCaM3 is a key component in the Ca 2+ -CaM HS signal transduction pathway.

Functional Characterization of Arabidopsis thaliana WRKY39 in Heat Stress

“…The role of WRKY39 as a positive regulator in thermotolerance is also consistent with possible regulation of WRKY39 by calcium, a second messenger in A. thaliana. Calmodulin (CaM) interacts with the WRKY39 protein (Park et al, 2005) and calcium is involved in HS in plants through CaM (Liu et al, 2008;Zhang et al, 2009). Calcium does not appear to be involved in the classic HS signaling pathways, i.e.…”

Recent Advances in Calcium/Calmodulin-Mediated Signaling with an Emphasis on Plant-Microbe Interactions

“…Phenotypic analysis showed that in normal growth conditions, atcam2-2 plants were indistinguishable from the wild type, while genetic analysis showed a reduced transmission of the atcam2-2 allele through the male gametophyte, and in vitro pollen germination revealed a reduced level of germination in comparison with the wild type. However, the atcam3 knockout mutant showed a clear reduction in thermotolerance after heat treatment at 45°C for 50 min (Zhang et al, 2009). Overexpression of AtCaM3 in either the atcam3 knockout or wild-type background significantly rescued or increased the thermotolerance, respectively.…”

A loss-of-function mutation in Calmodulin2 gene affects pollen germination in Arabidopsis thaliana

“…Interestingly, Zhang and colleagues found that while the thermotolerance of the cam3 knockout mutant was significantly reduced after the heat-shock treatment, cam2 seedlings showed a thermotolerance similar to the wild type (Zhang et al 2009). Taken together these results suggest the existence of a functional diversification not only for genes encoding different CAM isoforms (CAM3 and CAM7) but also for genes encoding for the same isoform (CAM3 and CAM2).…”

“…In Arabidopsis, only two members of this gene family have been functionally characterized, CAM3 (Zhang et al 2009) and CAM7 (Kushwaha et al 2008).…”

“…CAM7 is a transcriptional regulator involved in seedling development (Kushwaha et al 2008), while CAM3 plays a key role in heat-shock signal transduction (Zhang et al 2009). …”