CBL-CIPK pathways in the drought and salt stress response of Solanaceae: The role of CBL5

Adaptations to drought and salinity include many complex physiological changes, including attenuated growth, transient increases in ABA levels, accumulation of compatible solutes and protective proteins, and increased levels of antioxidants (Bartels et al. 2005). In these processes, many stress-related genes are up-regulated or down-regulated. With the help of high throughput DNA technologies, the search for stress-associated genes has been saturated, at least in Arabidopsis (Bartels et al. 2005). However, only a limited number of genes have been evaluated for their contributions to drought or salt tolerance, especially in agricultural plants, which limits the utilization of these genes for improving crop production under drought or salt stress (Bartels et al. 2005). Therefore, the identification and evaluation of key genes and their functional pathways need to be further explored in crop plants. The CBL–CIPK network plays an important role in the plant’s physiological development and the stress response, therefore it includes promising candidates and deserves more and further study. Reports on the CBL-CIPK network in Solanaceae crops are quite limited. Tobacco is widely considered as a model plant for fundamental research, because of its available high-quality genome sequence, easily-operated genetic transformation and short life span. Especially because it belongs to the Solanaceae just like tomato and potato, tobacco is a perfect model plant for unraveling stress-related genes in Solanaceous crops. The lab of Prof. Liu Haobao at the Tobacco Research Institute (TRI) of CAAS has been working on the functional analysis of CBL and CIPK family members in tobacco for many years, and have developed useful tools and plant materials. The common research strategy applied to elucidate the function of CBL and CIPK genes is based on homology-based cloning, and has shown to be successful. For example, our previous work on tobacco NsylCBL10 showed that it confers salt tolerance similar to AtCBL10 when overexpressed (Kim et al. 2007; Quan et al. 2007; Dong et al. 2015). Overexpression of CBL family member CBL5 was shown to confer salt and drought stress tolerance to Arabidopsis by others, but the underlying molecular mechanism is still unknown (Cheong et al. 2010). This project aims at identifying the role of tobacco NsylCBL5 in the drought and salt stress response, and to elucidate the stress response pathway that NsylCBL5 is involved in. The first aim is to describe phenotypes and understand the physiology of NsylCBL5-overexpressing lines and NsylCBL5-loss-of-function lines. This will give us insight in the function of NsylCBL5. Then we will unveil the upstream regulators and downstream targets of NsylCBL5 by molecular biological methods such as RNAseq, protein-protein interaction identification and yeast-library screening. Our final purpose is to further unravel the regulation pathway that is centered around the CBL5-CIPK complex under drought and/or salt stress in Solanaceae.