Abstract
Calmodulin-like (CML) proteins are primary calcium sensors and function in plant growth and response to stress stimuli. However, so far, the function of plant CML proteins, including tomato, is still unclear. Previously, it was found that a tomato (Solanum lycopersicum) CML, here named SlCML39, was significantly induced by high temperature (HT) at transcription level, but its biological function is scarce. In this study, the characteristics of SlCML39 and its role in HT tolerance were studied. SlCML39 encodes a protein of 201 amino acids containing four EF hand motifs. Many cis-acting elements related to plant stress and hormone response appear in the promoter regions of SlCML39. SlCML39 is mainly expressed in the root, stem, and leaf and can be regulated by HT, cold, drought, and salt stresses as well as ABA and H2O2. Furthermore, heterologous overexpression of SlCML39 reduces HT tolerance in Arabidopsis thaliana at the germination and seedling growth stages. To better understand the molecular mechanism of SlCML39, the downstream gene network regulated by SlCML39 under HT was analyzed by RNA-Seq. Interestingly, we found that many genes involved in stress responses as well as ABA signal pathway are down-regulated in the transgenic seedlings under HT stress, such as KIN1, RD29B, RD26, and MAP3K18. Collectively, these data indicate that SlCML39 acts as an important negative regulator in response to HT stress, which might be mediated by the ABA signal pathway.
Highlights
Calcium (Ca2+) is a key secondary messenger in eukaryotic cells which is involved in plant growth, development, and stress responses [1]
We found that a tomato (Solanum lycopersicum) calmodulin-like protein (CML) gene (Solyc11g071740) was significantly induced by high temperature (HT) at transcription level using RNA-seq analysis of HT-responsive genes in tomato leaves [24]
Our results indicate that as an important negative regulator, SlCML39 plays a role in HT stress response, which might be mediated by the ABA signal pathway
Summary
Calcium (Ca2+) is a key secondary messenger in eukaryotic cells which is involved in plant growth, development, and stress responses [1]. The Ca2+ signal is recognized by unique Ca2+ sensors, including calmodulin (CaM), calmodulin-like protein (CML), calcineurin B-like (CBL), and calcium-dependent protein kinase (CDPK) [1,2]. All these proteins have a conserved Ca2+ binding motif—“EF hand”—which binds to Ca2+ to cause conformational changes, followed by changes in activity to regulate downstream targets, thereby transmitting Ca2+ signals [3]. CMLs are closely related to CaMs, but their appearance is different from CaM, which has four EF hands. CMLs have one to six EF hands [4]. Despite so many CML genes, the functions of most plant CMLs are not well studied [8]
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