The Creation Of Maize Drought-tolerant Mutant Chang7-2t,and Study On Its Drought-tolerant Mechanism

Drought is one of the most common abiotic stress restricting maize production in China.Compared with improving ecological conditions and building water conservancy projects,it is more economical and effective to select and popularize maize varieties with drought tolerance and improve maize field drought tolerance.Maize breeders generally believe that there are many drought tolerance genes located in the genome of major maize cultivars and their parents' inbred lines.It is of great significance to explore and utilize these drought tolerance genes for maize drought tolerance breeding.Chang 7-2?C7-2? is an elite inbred line widely used in maize breeding in China.It has many advantages,such as high combining ability,strong resistance and short silk-spinning interval.In this study,maize mutants were selected from C7-2 seeds irradiated with ⁶⁰Co-?.Stable mutant inbred lines were obtained by continuous selfcrossing and field screening.The mutant C7-2t with strong drought tolerance was identified by comparing the physiological and biochemical indexes under field and control conditions.The mechanism of drought tolerance of drought tolerant mutants was analyzed from the level of transcriptome,proteome,and metabolome levels.In addition,the practical production significance of maize drought tolerant mutant was preliminarily explored by crossing the drought tolerant mutant with inbred line Z58.The main results of this paper are as follows1.Creation of maize drought-tolerant mutantThe maize mutant population was obtained by ⁶⁰Co-? irradiating on C7-2 seeds.With continuous selfcrossing and phenotypic screening under field conditions,mutant lines with uniform phenotype and excellent characters were selected.A mutant inbred line C7-2t with excellent drought resistance was obtained by combining with physiological and biochemical indexes under drought conditions.By the results of comparison on multiple physiological indexes such as the catalase activity,peroxidase activity,malondialdehyde content,soluble sugar content,it suggested that the tolerant mutants can grow normally under drought stress for a long time mainly because its efficient redox enzyme system and cell osmotic regulation,reducing the damage of drought stress on the cell membrane system,maintaining the leaf water balance under drought stress.The discovery of maize drought tolerant mutant C7-2t provides basic materials for maize cross breeding and drought tolerance mechanism research.2.Study on drought tolerance mechanism of maize drought-tolerant mutants by multi omicsTranscriptome sequencing was used to analyze the transcriptome of C7-2 and C7-2t leaves.Totally 4353 differentially expressed genes were detected in C7-2 under drought stress,with 2214 genes up-regulated and 2136 down-regulate;1034 differentially expressed genes were detected in C7-2t,of which 600 genes were induced and 434 genes inhibitied.A total of 835 differential genes were detected in both materials,and their expression trends were the same.In the coexpression set,520 genes were up-regulated and 315 genes down-regulated.It was found that drought significantly inhibited the expression of photosynthesis related genes in C7-2 and hindered the accumulation of organic in C7-2.Under drought stress,the expression of carbon metabolism-related genes of C7-2t was changed,and sucrose accumulation in leaves increased.C7-2t could regulate the activity of oxidoreductase through transcriptional level,and enhanced the regulation of cell wall growth,so as to maintain stable growth under drought stress.qPCR and Western blot were used to study the expression patterns of the two genes?DHN1 and Expansin-like A1?under drought stress.It was found that drought can induce the expression of dehydrin DHN1 and Expansin-like A1.Moreover,the accumulation of dehydrin protein in C7-2t leaves was higher than that of C7-2 under both control and drought conditions.In addition,post-transcriptional modification of the dehydrin gene may be present in C7-2t under drought stress.Drought stress induced the expression of expansin protein at the transcription and translation levels,and the higher content of expansin protein and cellulose in C7-2t leaves under control conditions contributed to the biosynthesis of drought-tolerant mutant cell walls.Therefore,the accumulation of dehydrin and expansin protein in C7-2t may be an important molecular mechanism for drought-tolerant mutants to achieve excellent drought-resistance.In addition,the higher content of JA in leaves of C7-2t under control conditions might be related to the accumulation of DHN1 and expansin-like A1.The accumulation of DHN1 and expansin-like A1 in C7-2 leaves might be related to the synthesis of drought-induced ABA.3.Application of drought-tolerant mutant C7-2tThe hybrid F1 was obtained by crossing C7-2t with Z58,and ZD958 were employed as control to study the different performance at seedling stage in field under controlled conditions.It was found that the external morphology of C7-2t could be transferred to F1 progenies by crossing.In addition,compared with ZD958 the offspring of drought-tolerant mutant had better drought resistance index and maintained high photosynthetic efficiency for a long time under drought stress.After investigating the characters of C7-2,C7-2t,ZD958 and F1 harvested in the field,it was found that C7-2t and F1 had shorter barren ear tip when pollinating female panicles with the same silkproducing days.The results of field investigation showed that the F1 generation had the same spinning time and did not affect the field yield.These results will provide new clues for maize drought stress response mechanism.The results are of great significance for enriching maize germplasm resources,improving maize drought tolerance and breeding new drought-tolerant maize varieties.