Screening Of Salt-tolerant Maize Germplasm And Functional Study Of ZmSWEET1b Gene In Response To Salt Stress

Maize is a salt-sensitive crop.Increasing soil salinization has become one of the main environmental stresses leading to the decline of maize yield and quality.It is of great significance to explore the regulatory factors associated with salt tolerance of maize and to study the salt tolerance mechanism of maize.In this study,10 maize inbred lines from different heterosis groups were selected,and the salt tolerance of maize was analyzed by artificial pot experiment.The identified salt-tolerant and salt-sensitive inbred lines were used as experimental materials for transcriptome sequencing analysis,and then the salt stress response factors of maize were excavated.Finally,the corresponding gene function of salt stress was studied by constructing related gene editing materials.The main results are as follows:(1)Ten maize inbred lines were treated with 100 mM NaCl to simulate the salt stress environment.The phenotypic differences of maize seedlings under normal water treatment were compared and observed.Two salt-sensitive maize inbred lines SS1(salt sensitivity 1)and SS2(salt sensitivity 2)were identified by the determination of fresh and dry weight agronomic traits and the measurement of SPAD value,Na+and K+content.Two salt-tolerant maize inbred lines ST1(salt tolerance 1)and ST2(salt tolerance 2).Salt stress significantly inhibited the growth and development of salt-sensitive inbred line SS1 and broke its ion balance.The salt-tolerant inbred line ST1 resisted salt damage by maintaining a higher relative water content and a higher K+/Na+ under NaCl stress.(2)The maize salt-tolerant inbred line ST1 and salt-sensitive inbred line SS1 were selected,and the root tissues of maize seedlings at three-leaf stage under normal water treatment and 100 mM NaCl treatment were sampled for transcriptome sequencing analysis.The results showed that under NaCl stress,there were 718 differentially expressed genes in SS1,388 up-regulated and 330 down-regulated.There were 1244 differentially expressed genes in ST1,576 up-regulated and 668 down-regulated.The expression patterns of 18 common DEGs in SS1 and ST1 were opposite.Among them,ZmSWEET1b was up-regulated in ST1 and down-regulated in SS1,which was a positive regulator of salt stress.GO enrichment analysis showed that differentially expressed genes were mainly involved in biological processes such as oxidative stress response and stress response.(3)ZmSWEET1b is a typical member of SWEET family with seven transmembrane helices and plasma membrane localization.CRISPR/Cas9 technology was used to edit the two targets in ZmSWEET1b,and two homozygous editing lines CR#1 and CR#2 were obtained.The salt tolerance investigation and expression analysis of CRISPR/Cas9-edited lines showed that the ZmSWEET1b CRISPR/Cas9 gene-edited lines became more sluggish after salt treatment.ZmSWEET1b knockout lines may increase the sensitivity to salt stress by reducing the transcriptional abundance of Na+efflux related genes(ZmSOS1,ZmH+-ATPASE 2 and ZmH+-ATPASE 8)from root to rhizosphere.