Preliminary Functional Identification Of SPL Transcription Factors In Response To Salt And Drought Stress In Cotton (Gossypium Hirsutum L.)

In recent years,due to the drastic changes of climate and environment,natural disasters occur frequently,which pose a serious threat to the growth and yield of crops.Saline alkali and drought are two main abiotic stress factors that harm the growth and development of plants.It is of great practical significance to explore the potential salt and drought stress response genes,analyze the mechanism of stress resistance,and improve the salt and drought tolerance of cotton.SQUAMOSA promoter-binding protein-like proteins（SPLs）are a class of plant specific transcription factors,including a highly conserved SBP-box domain,involved in plant growth and development,as well as biological and abiotic stress response.In this study,the candidate SPL genes of salt and drought tolerance were mined in upland cotton,and the preliminary functional analysis of the candidate genes was carried out,so as to lay a foundation for further functional analysis of these SPL genes.The main results are as follows:1.Screening of SPL genes related to salt and drought stress response and obtaining of candidate genes:six GhSPL genes GhSPL5b/5c/5d,GhSPL8a,GhSPL10b and GhSPL14a were selected as candidate genes related to salt and drought stress response through inducing expression patterns of all 59 SPL transcription factors at different stages after salt and drought treatment and combining with expression patterns of different tissues and organs.Further quantitative expression verification of the six SPL genes:three genes（GhSPL5d,GhSPL8a and GhSPL14a）were up-regulated under salt stress,and four genes（GhSPL5b,GhSPL5c,GhSPL5d and GhSPL8a）were up-regulated under drought stress,which suggested that they might be involved in the response of cotton to salt/drought stress.2.Salt tolerance verification of three candidate SPL genes related to salt stress response.After 30 days of treatment with 300m M Na Cl,the three gene silenced plants respectively and TRV2:00 injected plants were identified by morphological and physiological indexes and root phenotype.Compared with TRV2:00,the relative plant height of TRV2:GhSPL5d plant decreased significantly,the relative MDA accumulation decreased significantly,and the relative PRO accumulation increased significantly between water and salt treatments;compared with TRV2:00 plant,the relative plant height of TRV2:GhSPL8a plant decreased significantly,the relative shoot and root dry matter decreased significantly,and the relative PRO accumulation increased significantly between water and salt treatments;compared with TRV2:00,the relative plant height of TRV2:GhSPL14a plants decreased significantly,the relative shoot and root dry matter decreased significantly,the relative SOD activity increased significantly,and the relative PRO accumulation increased significantly between water and salt treatments.The root scan data showed that:in the salt treated plants,the GhSPL5d,GhSPL8a and GhSPL14a gene silenced plants were significantly larger than the TRV2:00 plants.3.Drought resistance verification of four candidate SPL genes related to drought stress response.Four gene silenced plants respectively and TRV2 injection plants were treated with 15%PEG treatment,after 20 days of treatment,samples were taken for physiological index determination,and after 30 days of treatment,morphological and root phenotype identification were carried out.Compared with TRV2:00,the relative H₂O₂ accumulation of TRV2:GhSPL5b plants decreased significantly between water and drought treatments.Compared with TRV2:00,the relative root dry matter of TRV2:GhSPL8a and TRV2:GhSPL5c plants decreased significantly between water and drought treatments.TRV2:GhSPL5d plants did not show significant differences in indexes.The root scan data showed that:in drought treatment plants,GhSPL5b,GhSPL5c and GhSPL8a gene silenced plants were significantly larger than those injected with TRV2:00,while there was no significant difference between GhSPL5d gene silenced plants and those injected with TRV2:00.In conclusion,it is suggested that among the three candidate SPL genes（GhSPL5d,GhSPL8a and GhSPL14a）related to salt stress response,the comprehensive utilization value of GhSPL8a and GhSPL14a genes was in the first place,and the plant phenotype was more obvious.Among the four candidate SPL genes（GhSPL5b,GhSPL5c,GhSPL5d and GhSPL8a）related to drought stress response,the comprehensive utilization value of GhSPL5b and GhSPL8a genes was in the first place,and the plant phenotype was more obvious.This study provides candidate genes for further functional analysis of SPL genes in response to stress in cotton.