Transcriptomic analysis of the succulent xerophyte Zygophyllum xanthoxylum in response to salt treatment and osmotic stress

Abstract

Accumulating a great quantity of Na+, maintaining the stability of the concentration of important nutrition elements, increasing the activities of enzymes related to ROS-scavenging are crucial strategies for the xerophyte Zygophyllum xanthoxylum surviving under adverse saline and drought environments; besides, actively regulating the photosynthesis is also a main reason for Z. xanthoxylum to adapt to mild salt conditions. However, the possible molecular basis of above physiological mechanisms is poorly understood. By performing Illumina sequencing combined with a digital gene expression profiling technique, differentially expressed genes in leaves and roots of Z. xanthoxylum under 50 mM NaCl and −0.5 MPa osmotic stress for 6 and 24 h were identified, respectively, mainly focused on genes related to ion transport, ROS-scavenging system and photosynthesis. Under 50 mM NaCl and −0.5 MPa osmotic stress, the transcripts of genes encoding transporters/channels for Na+, K+, Ca2+, Mg2+, nitrogen, phosphate and important micro-elements significantly increased, which is conducive to enhance the uptake and transport of nutrient elements in Z. xanthoxylum; and more importantly, besides Na+, genes related to vacuolar compartmentalization of K+, Ca2+, NO3 − in leaves plays vital roles in the adaptation to mild salt condition. Meanwhile, NaCl treatment and osmotic stress significantly increased the transcripts of a number of genes related to ROS-scavenging system, which is beneficial to accelerate the ROS-scavenging under 50 mM NaCl and mitigate the damage of ROS to cell biomembrane system under osmotic stress. In addition, in contrast to osmotic stress, 50 mM NaCl significantly induced the expression of genes encoding proteins participated in photosynthetic electron transport and carbon fixation, while inhibited the expression of genes related to chlorophyll catabolism. The present study identified potential genes underling the principal physiological mechanisms of salt and drought tolerance in Z. xanthoxylum. The results provided abundant genetic resources from desert xerophyte for genetic improvement of stress-resistance of important forage and crop species in arid area.