Molecular Mechanism Of Salt Resistance Of Chlamydomonas Reinhardtii And Dicranum Scoparium Based On Comparative Transcriptome

Soil salinization causes many plants to wither and die,and it has become one of the most significant abiotic stresses that threaten plant growth and agricultural productivity in a global scale.In this study,Chlamydomonas reinhardtii and Dicranum scoparium,which have certain stress resistance characteristics,were used to determine the molecular basis of salt resistance by transcriptome sequencing.The related responses of the plants base groups were determined based on the genetic homologue among species and the common characteristics of salt stress adaptation.The primary results of the study are as follows:10635 differentially expressed genes were discovered in C.reinhardtii in 24 hours under 200m M salt stress,including 5920 up-regulated genes and 4715 down-regulated genes,focusing on 30genes with significant differential expression.Using GO and other functional enrichment analysis on the differentially expressed genes,it was revealed that the upregulated unigenes were enriched to353 biological processes,and the downregulated unigenes were enriched to 313 biological processes.The primary response process has been discovered and analyzed as follows:under stress,the condensation protein complex subunits related to programmed cell death regulatory proteins and the genes related to stress-resistant fibrin family are significantly up-regulated;calcium-binding proteins such as calreticulin are significantly up-regulated,where algae respond to salt stress by accommodating osmotic or steady-state regulation through Ca²⁺signaling pathway;Genes that are related to Lysophosphatidic acid acyltransferase,which is responsible for the synthesis of lysophosphatidic acid,are up-regulated,where algae maintain lipid homeostasis by regulating phospholipid acid;genes involved in oxidative stress and heat shock proteins,such as glyceraldehyde-3-phosphate dehydrogenase C subunit 1 and fumarase 1-related genes,are up-regulated,which is conducive to protein renationalization and ion homeostasis;It has been conjectured that C.reinhardtii can reduce the accumulation of carbohydrates in cells by enhancing glycolysis metabolism,thus promoting respiratory metabolism and reducing ionic toxicity and osmotic stress caused by salt damage;C.reinhardtii also uses trehalose as an alternative energy source to maintain the homeostasis of its internal environment.16153 differentially expressed genes were discovered in D.scoparium in 24 hours under 200m M salt stress,including 6646 up-regulated genes and 9507 down-regulated genes.The biological processes were clustered by REVIGO.248 BPs rich in up-regulated genes were categorized into10 groups,and 225 BPs rich in down-regulated genes were categorized into 12 subsets.The primary response is the upregulation of calmodulin and calcium-dependent protein kinase genes,which is consistent with the previously reported Ca²⁺signal components and transcription factors related to salt response,indicating its potential function in salt resistance of bryophytes.In addition,the expression of ABA synthesis enzymes,ABA receptor related genes,and some ABA-related transcription factors were also up-regulated in bryophytes under salt stress,which revealed the potential mechanism of ABA signaling pathway in bryophytes.The reconstruction of ion homeostasis in bryophytes may depend on the high expression of different ion transmembrane transporters to regulate the balance of Na⁺and K⁺in bryophytes.Between bryophytes and algae,the gene sets of the up and down-regulated genes identified by the expression pattern and the gene sets categorized from responses to the salt stress were studied respectively in order to identify the homologous gene that is responsible for salt stress responses in bryophytes and algae.A comparison of the up and down-regulated gene sets and the salt stress response gene sets containing differentially expressed genes in algae and bryophytes was conducted to unveil several fundamental similarities in mechanisms of the two species responding to salt stress:1.Since the homologous gene of calmodulin is up-regulated in bryophytes and algae,Ca²⁺may play a conservative role in the process of plant stress resistance by regulating the stress-induced CAM membrane transporter in bryophytes and algae.2.Under salt stress,the homologous gene CPK6 of Arabidopsis increased continuously in bryophytes and algae,indicating the similar mechanism of response of CDPKs to salt stress.3.The synthesis genes related to membrane phospholipid signaling members were up-regulated in the salt stress group,indicating that phospholipid signaling phosphatic acid（PA）plays a conservative role between bryophytes and algae.4.Coenzyme NCED3,the first enzyme involved in abscisic acid biosynthesis,was up-regulated in algae and bryophytes.It is predicted that ABA3（（Abscisic acid-insensitive 3））is also a functional conservative gene in bryophytes and algae.The function and evolution of ABA biosynthesis gene in plant basic groups are relatively conservative.5.The homologous genes of Na⁺/H⁺exchange protein family（NHXs）were continuously up-regulated in salt stress samples,indicating the conservative mechanism of these genes in maintaining ion homeostasis under salt stress.In addition to the aforementioned potential functional gene sets with similar expression patterns in algae and bryophytes when under salt stress,there are also some gene sets containing genes that are specifically up-regulated in bryophytes,such as CBL-CIPKs complex related to calcium ion efflux.In this study,the direct homologous gene set of CBL1 in Arabidopsis and the gene set of CIPK26 in bryophytes are specifically up-regulated.In bryophytes,the transcription factor DREB2A–Dehydration Responsive Element Binding Protein 2A-of AP2/ERF family is a homologous gene,and GRF7-Growth Regulating Factor 7-interacts with the DREB2A promoter.The homologous genes of GRF7,CHX17 and HAK5 which are related to ion transport processes under salt stress conditions,SNF1-related protein kinase（Sn RK2）,and 2C type protein phosphatase ABI1 which regulate many downstream pathways of ABA signaling pathway,were up-regulated under salt stress.Many of the genes here have no homologous genes or copies in algae.The above results have shown that with the evolution of plants,many salt stress response processes are accompanied by the occurrence of plants,and a series of stress-resistant genes within the plant groups have gradually evolved,such as new genes related to ion-loading or new functional genes generated after the replication of that gene’s family.