CML9, a multifunctional Arabidopsis thaliana calmodulin-like protein involved in stress responses and plant growth?

Abstract

Plants have evolved complex signaling networks to respond to their fluctuating environment and adapt their growth and development. Calcium-dependent signaling pathways play key role in the onset of these adaptive responses. In plant cells, the intracellular calcium transients are triggered by numerous stimuli and it is supposed that the large repertory of calcium sensors present in higher plants could contribute to integrate these signals in physiological responses. Here, we present data on CML9, a calmodulin-like protein that appears to be involved in plant responses to both biotic and abiotic stress. Using a reverse genetic approach based on gain and loss of function mutants, we present here data indicating that this CML might also be involved in root growth control in response to the flagellin, a pathogen-associated molecular pattern (PAMP) also involved in plant immunity.

Figure 1. Primary root growth analyses of CML9 genotype in reponse to flagellin treatment (A) Wild-type (Col), cml9 genotypes (KO cml9–1 and OE-CCs lines) and fls2 mutant seedlings grown for 7 d in MS medium (control, upper panel) in presence or not of flg22 1µM (lower panel). (B) Quantitative analyses of the primary root growth under control condition (MS) or after flagellin treatment (MS + flg22). The experiments were performed using three independent biological replicates and each histogram represents the mean root length (± SEM) analyzed using 20 to 24 independent roots per genotype. Statistical differences between the genotypes treated or not by flg22 are detected by ANOVA analysis followed by Tukey’s HSD test, at p < 0.05.

Figure 2. Hypothetical model involving CML9 in flg22-induced plant growth inhibition through GA-dependent signaling pathway. (A) Model of plant growth control through GA-dependent signaling. Upon GA binding to its soluble receptor (GID1), signaling pathway is activated; DELLA proteins are degraded via the ubiquitin-proteasome pathway. The major players of this GA-signaling cascade are the GA receptors (GID1), the DELLA repressor proteins and the F-box protein part of the SCF E3 Ubiquitin ligase complex. DELLAs are nuclear transcriptional regulators, which interact with other transcription factors (i.e. GA-TF, GA-dependent transcription factor) to modulate expression of GA-responsive genes. (B) Working model of flg22-induced plant growth inhibition that involve GA signaling cascade components and CML9.