Comparative transcriptome analysis of salt-sensitive and salt-tolerant maize reveals potential mechanisms to enhance salt resistance.

BACKGROUND: Salt stress is a devastating environmental stress that causes plant growth inhibition and yield reduction.

OBJECTIVE: The identification of salt-tolerant genes brings hope for the generation of salinity-tolerant crop plants through molecular breeding.

METHODS: In this study, one salt-sensitive and one salt-tolerant maize inbred line were screened from 242 maize inbred lines. Reactive oxygen species (ROS)-related enzyme activities were detected and salt-responsive comparative transcriptome analysis was performed for control and 220 mM NaCl treated maize leaves.

RESULTS: Salt-tolerant maize inbred line (L87) showed higher ROS-related enzyme (SOD, POD, APX and CAT) activities and accumulated relatively lower levels of ROS under salt stress. Of the total DEGs, 1856 upregulated DEGs were specific to L87, including stress tolerance-related members of the 70kDa family of heat shock proteins (Hsp70s) and aquaporins. The DEGs involved in the abscisic acid (ABA), ethylene, jasmonic acid (JA) and salicylic acid (SA) signal transduction pathways may determine the difference in salt tolerance between the two varieties, especially one central component SnRK2, that positively regulates ABA signaling and was only upregulated in L87. Analysis of DEGs related to ROS scavenging showed that some peroxidase (POD), glutathione S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) genes specific to L87 probably enhanced its salt tolerance. The analysis of differentially expressed transcription factors (TFs) suggested that WRKY TFs could contribute to the difference in salt tolerance between the two maize lines.

CONCLUSION: Compared with Salt-sensitive maize inbred line (L29), L87 exhibits specific regulatory mechanisms related to salt tolerance, including plant hormone interactions, ROS scavenging and the regulation of TFs. Our study identifies new candidate genes that may regulate maize tolerance to salt stress and provides useful information for breeding maize with high salt resistance.