Physiological And Transcriptome Study Of Sonchus Oleraceus L.Response To Salt Stress

Soil salinization is the main abiotic stress that effects plant development,production and distribution.Exploitation of saline soil is an important combination of efficient utilization of land resources and improvement of ecological environment.Studying the salt-tolerant plant species,revealing the salt tolerance and various levels of regulation mechanisms and promoting the cultivation in saline soil is an economic and sustainable way to exploit and improve the saline soil.We selected the Sonchus oleraceus L.seedings as study material.S.oleraceus seedings were cultivated in soil and irrigated with water containing NaCl of 0(CK),66,133,200,250,300,400 mM for 15 days to study the effect of salt stress on plant growth;S.oleraceus seedings were irrigated with Hoagland's nutrient solution containing NaCl of 0(CK),66,133,200,250,300 mM for 3 days to evaluate the physiological responses of plant to salt stress.Full-length transcript of S.oleraceus was sequenced using PacBio platform.We selected seedlings that were treated with 200,250,300 mM NaCl for 2d to research the expression profile that used the full-length transcript as reference sequence to study the key genes and metabolic pathways of S.oleraceus response to salt stress.(1)Salt stress significantly influenced the growth of S.oleraceus.The effect on above-ground biomass was greater than it on below-ground biomass.More assimilation products were distributed to the below-ground of S.oleraceus with the treatment of 66-250 mM NaCl,from which promoting the growth of root,increasing the ratio of root biomass / shoot biomass,promoting water absorbtion of roots and keeping alive of S.oleraceus seedings.(2)After 1,2 and 3 days of salt treatments,K~+,soluble sugar,soluble protein and proline contents,SOD,POD and CAT activities significantly increased with the increased salinity then decreased.Na~+ content and K~+ / Na~+ had the similar tendency after 1 and 2 days salt treatments.After 3 days of salt stress,Na~+ and proline content significantly increased with the increased salinity,MDA content significantly increased when NaCl > 200 mM,But the changes of K~+ / Na~+ were not obvious.(3)Full-length transcript of S.oleraceus was sequenced and generated 50286 final consensus isoforms.Total base length were 104 million bp and mean base length was 2078 bp(N50=2303).Expression profiles of S.oleraceus leaves was studied,raw data size of every sample > 1.1 G and Q20 > 97%,generated average of 23.18 million clean reads.(4)Annotation analysis of GO database and pathway enrichment analysis of KEGG were performed for different expressed genes.Salt stress induced the expression of a large number of genes.Carbohydrate,amino acid and protein metabolic pathways were significantly enriched and osmopretectants,stress proteins,antioxidant were induced to synthesize.The main transport and catabolism pathway were endocytosis and phagosome.Circadian rhythm was induced with the treatment of 300 mM NaCl.In conslusion,S.oleraceus was very salt tolerant and could tolerance 66-300 mM NaCl,as judged from the higher ability to absorb K~+ and reject Na~+ as well as the higher osmoregulation and antioxidant capacity,almost relieving the toxicity of Na~+ and osmotic stress.But the osmoregulation and antioxidant capacity decreased when NaCl > 200 mM.The study on the expression profile of S.oleraceus found that,salt stress induced the expression of stress protein,antioxidant,osmopretectant and endocytosis and phagosome related genes,promoted a series of physiological metabolic pathways to relieve the damage caused by salt stress.On the basis of the physiological characteristics,key genes and metabolic pathways of S.oleraceus response to salt stress,providing the theoretical basis for the exploitation and cultivation of S.oleraceus in salinity soil.