Genome-Wide Association Analysis Of The Genetic Basis Of Chlorophyll Degradation Rate Of Maize Husks

Maize is one of the three major food crops in China.It is widely used in daily production and life as a raw material for food,feed and industry.With the intensive adjustment of maize planting structure and the lack of human resources,mechanized harvesting of maize has become an inevitable trend in agricultural development.The traits of tightness and grain moisture of maize during physiological maturity are important factors affecting the mechanical harvesting of maize.These traits are closely related to senile senescence.The degradation of chlorophyll is the main indicator of plant senescence.Studies have shown that the senescence of leaves is significantly positively correlated with the decrease of chlorophyll content in leaves.Most of the previous studies on the senescence of maize leaf stalks stayed on the phenotypic traits of loquat leaves,and did not deeply understand the molecules and their regulation mechanisms of chlorophyll degradation rate during senescence of loquat husks.The experiment used associations from 508 maize inbred lines with extensive polymorphisms from three different regions(China,USA,and Mexico International Maize Improvement Center),which were used in the Fushun environment in 2017 and the Shenyang environment in 2018.Repeated planting was performed twice in a randomized block manner.The chlorophyll content of the husks of maize was measured by remote sensing chlorophyll meter,and the data were analyzed.The phenotypic data of the target traits of maize chlorophyll degradation rate and the high-density single-nucleotide polymorphism molecular markers(SNPs)covering the whole genome of maize were subjected to genome-wide association analysis(GWAS),which were screened to obtain target traits.Significantly related independent SNP loci are used to find candidate functional genes that may be involved in the regulation of target traits through these SNP loci.The main findings are as follows:The chlorophyll degradation rate of maize stalk husks showed a wide range of natural variability,which was consistent with normal distribution and belonged to quantitative traits regulated by multiple genes.The chlorophyll degradation rate of maize husks was slightly different under different environments.The chlorophyll degradation rate of maize chlorophyll was analyzed by variance,and the results showed that its generalized heritability was 0.62.A total of 21 significantly independent SNP loci were obtained by GWAS analysis of the chlorophyll degradation rate of maize cultivars,which were distributed on eight chromosomes except for Chr.1 and Chr.10.According to these 21 SNP loci,a total of 87 candidate genes related to the chlorophyll degradation rate of maize locust husks were found.By comparing the functions of Arabidopsis thaliana and rice homologous genes,the 87 genes were functionally analyzed and divided into seven categories according to their metabolic pathways: transcription pathway,signal transduction pathway,transport pathway,nucleic acid editing pathway,Redox pathways,metabolic pathways,and unknown pathways,Finally,five candidate functional genes of GRMZM2G137984,GRMZM2G035370,GRMZM2G113866,GRMZM2G074438,GRMZM2G371176 were screened from these genes,which may be involved in the regulation of chlorophyll degradation rate in maize husks.