Transcriptional and metabolic profiles revealed the difference in grapevine (Vitis vinifera) plants responses to neutral salt stress and alkali salt stress
Authors: Lu Xu , Ma Lei , Zhang CongCong , Yan HaoKai , Bao JinYu , Gong MeiShuang , Wang WenHui , Li Sheng , Ma ShaoYing , Chen BaiHong 
Published: July 2022

Abstract
Salt stress and alkali stress were two abiotic stressors which largely impact plant growth and development in grapevine (Vitis vinifera) plants. However, little is known about the mechanisms of grapevine plants response to salt stress and alkaline stress, and whether salt stress and alkali stress have differences in grapevine plants is still unidentified. Thus, we measured physiological parameters, identified chloroplast structure, and analyzed transcriptomics and metabolomics data to characterize the acclimation and difference of grapevine plant under neutral salt stress and alkali salt stress. The results showed that grapevine plants under salt stress and alkali stress were both accompanied by chlorosis of leaf, a decline in photosynthetic capacity, decrease in chlorophyll content and Rubisco activity, imbalance of Na+ and K+, and poorer chloroplast ultrastructure, compared with control. The chlorophyll fluorescence index (Fv/Fm, NPQ) showed the different response to salt stress and alkali stress. Fv/Fm were both decrease in salt stress and alkali stress, whereas NPQ were only decreased in alkali stress. Alkali stress led more serious damage to phenotype, chloroplast microstructure and physiological characteristics in grapevine plants than salt stress. Transcriptomic data showed that salt stress and alkali stress induced the differential expression of stress genes involved in ABA signal and MAPK signal pathways as well as up-regulation of gene encoding ion transporter such as AKT1, HKT1, NHX1, NHX2, TPC1A and TPC1B. However, alkali stress induced more down-regulated genes in ‘Porphyrin and chlorophyll metabolism’, ‘Photosynthesis-antenna proteins’ and ‘Photosynthesis’ pathways compared with salt stress, and both two salt stresses induced many down-regulated DEGs in ‘Carbon fixation in photosynthetic organisms’ pathway. Metabolomics data showed that two substrate involved in chlorophyll synthesis including L-Glutamic acid were down-regulated both under salt stress and alkali stress, but 5-Aminolevulinate (ALA) were only down-regulated under salt stress. In the ‘Carbon fixation in photosynthetic organisms’ pathway, two salt stresses commonly induced the increase of key metabolites including D-Sedoheptuiose 7-phosphate, D-Erythrose-4-phosphate and Dihydroxyacetone phosphate involved in Calvin cycle, but 3-Phospho-D-glyceric acid, D-Fructose 6-Phosphate and Sedoheptulose showed converse change. Many sugar metabolites showed decreased levels under salt stress. However, alkali stress induced an increase in 7 sugar metabolites including Rhamnose, Sedoheptulose, D-Sedoheptulose 7-phosphate, D-Fructose 6-Phosphate, D-Glucose 6-phosphate, Solatriose and Raffinose. Taken together, our results showed that salt stress and alkali stress affected the plant phenotype, chloroplast structure, gene expression and metabolite abundance, and alkali stress resulted in more serious damage to grapevine plants than that of salt stress.