Transcriptome Analysis Of Rice Under Salt Stress And Functional Investigation Of Salt Tolerance Related Genes

Salt stress is one of the main factors responsible for the low yield of crops. Thus, many botanists focused on molecular mechanisms of plant responses to salt stress and to improve crop salt tolerance. Using 10K rice cDNA microarray, we identified 486 salt-responsive ESTs (representing 450 unigenes) in shoot of a high salt tolerant indica variety, Nona Bokra(Nona). Among them, 175 genes have been characterized as salt responsive genes previously, and the rest were identified for the first time in this study. According to the cluster result, these ESTs/genes could be classified into five groups. Functional category analysis of each group revealed some important mechanisms contributing to salt tolerance of Nona. For example, transcription factors and kinases were dominantly presented in those transiently induced genes (Group I), which implied transcription regulation and signal transduction could be immediately activated in Nona and multiple transcription regulation pathways were involved in salt stress. Those genes in cell damage control and repair category and transporter category were mostly induced within 3 hours. Further more, hierarchical cluster and function category analysis also revealed other interesting phenomena, such as crosstalk between salt stress and senescence and transcriptional repression of photosynthesis.We also compared transcriptome changes between Nona and the salt hypersensitive variety IR28 under salt stress. The result showed regulations of many salt responsive genes were impaired in IR28, and some of those genes have been demonstrated to be essential for plant salt tolerance. It suggested the hypersensitivity of IR28 was, at least partially, due to the impairment of transcription regulation..Moreover, we investigated calcium signal impacted on salt responsive genes. Interestingly, pretreatment with EGTA, a calcium signal inhibitor, lead to a mimic transcriptome under salt stress, and only those genes regulated after 24 hours under salt stress were observed to be inhibited by EGTA. Although the physiological experiment showed a great consistency with the result of microarray, it is a challenge to give a reasonable and credible explanation for these results.Among these salt responsive genes, we selected one, OsTPP1, for further functional analysis. The expression pattern analysis confirmed the result of microarray and showed OsTPP1 was also rapid and transiently induced under drought stress. On the other hand, overexpression of OsTPP1 remarkably enhanced rice salt tolerance. This study showed a preliminary result for roles of OsTPP1 under salt stress.