Comparative Transcriptomics Reveals Osmotic and Ionic Stress Key Genes Contributing To Salinity Tolerance Differential in Two Pak Choi Cultivars

Background: Pak choi is an important leafy vegetable crop. Salinity is among the most harmful agents that negatively influence pak choi yield. However, the mechanism of salinity tolerance in pak choi has not been well understood. In this study, the root transcriptomics of two cultivars differing in salinity tolerant, Shanghaijimaocai (S, salinity tolerant) and Te’aiqing (T, salinity sensitive), were investigated under 0 and 100 mM NaCl treatments.Results: Using de novo assembly, 214,952 assembled unigenes were generated. Totals of 6765, 2454, 2451 and 5798 differentially expressed unigenes (DEUs) were identified in comparison of S100/S0, T100/T0, S0/T0 and S100/T100, respectively. Shanghaijimaocai is more sensitive to NaCl stress than Te’aiqing in terms of root transcriptomics. Based on GO and KEGG pathway analysis, several osmotic and ionic stress-related genes including MP3K18, PYL8, PP2C15/16/49, ARF2, bHLH112, bZIP43, COL5, CDF1/3, ERF25/60, HSFA6, MYBS3/59/92/CCA1/PHL5, POD21, GOLS7, CIPK4/7/12, NHX7, SLAH1 and ALMT13, showed higher expression in Shanghaijimaocai than in Te’aiqing. These genes, therefore, might be contributed to the difference in salinity tolerance. Moreover, the physiological shift of peroxidase activity was in accordance with dynamic transcript profile of the relevant unigenes. Conclusions: We determined digital expression profile and discovered a broad survey of unigenes associated with the difference of salinity tolerance between Shanghaijimaocai and Te’aiqing. These findings would be useful for further functional analysis as potential targets to improve resistance to salinity stress via genetic engineering.