Identification of candidate genes related to salt tolerance of the secretohalophyte Atriplex canescens by transcriptomic analysis.

Background: Atriplex canescens is a typical C secretohalophyte with salt bladders on the leaves. Accumulating excessive Na in tissues and salt bladders, maintaining intracellular K homeostasis and increasing leaf organic solutes are crucial for A. canescens survival in harsh saline environments, and enhanced photosynthetic activity and water balance promote its adaptation to salt. However, the molecular basis for these physiological mechanisms is poorly understood. Four-week-old A. canescens seedlings were treated with 100 mM NaCl for 6 and 24 h, and differentially expressed genes in leaves and roots were identified, respectively, with Illumina sequencing.

Results: In A. canescens treated with 100 mM NaCl, the transcripts of genes encoding transporters/channels for important nutrient elements, which affect growth under salinity, significantly increased, and genes involved in exclusion, uptake and vacuolar compartmentalization of Na in leaves might play vital roles in Na accumulation in salt bladders. Moreover, NaCl treatment upregulated the transcripts of key genes related to leaf organic osmolytes synthesis, which are conducive to osmotic adjustment. Correspondingly, aquaporin-encoding genes in leaves showed increased transcripts under NaCl treatment, which might facilitate water balance maintenance of A. canescens seedlings in a low water potential condition. Additionally, the transcripts of many genes involved in photosynthetic electron transport and the C pathway was rapidly induced, while other genes related to chlorophyll biosynthesis, electron transport and C carbon fixation were later upregulated by 100 mM NaCl.

Conclusions: We identified many important candidate genes involved in the primary physiological mechanisms of A. canescens salt tolerance. This study provides excellent gene resources for genetic improvement of salt tolerance of important crops and forages.