Phenotypic Plasticity Of Maize Husk Via Genome-wide Association Study

Maize,as one of the three important crops in China,is not only used for food but also for feed,industry and the medicine.Husk is the modified leaf sheath enclosing the ear of maize.Its morphological structure is closely related to the dehydration rate and mechanical harvest of maize kernel.Maize husk can maintain the normal growth and development of ear,and protect ear from pests and diseases.It is also an important nutrient storage organ,which participate in photosynthesis for providing the energy of kernel development.Previous study has found that maize husk have significant differences in different environments.The ability with same genotype exhibiting different phenotypes in different environments,was known as phenotypic plasticity.It reflected the relationship between biology and the environment.It had become a key issue in the study of ecology and genetics.In this study,the environmental variance was used as a phenotype for Genome-wide association study(GWAS)to analyze the genetic basis of phenotypic plasticity of husk traits.Our aim was to provid a theoretical basis for stable heredity and off-site breeding of husk traits.This study used a population of 508 maize inbred lines with extensive polymorphism as materials.All lines were planted in three region with large environmental differences,the southern region of Sanya in 2014,the northern region of Beijing in 2015(China Agricultural University Shangzhuang Experimental Station)and 2017 Tieling.There were two replicates in Sanya and Beijing,and three replicates in Tieling.After the maize kernel completed maturation,the maize husk traits(length,width,number and thickness)was analyzed at the same time before harvest.The phenotypic plasticity was calculated by the environmental variance in GWAS.According to the Farm CPU algorithm,GWAS analysis was performed on the phenotypic plasticity of husk traits,and the significantly associated single nucleotide polymorphism(SNP)sites were identified to find candidate genes.The results showed that there were significant differences among different environments for the same husk trait.Thus,the environmental variance should be used as the phenotype of phenotypic plasticity in this study.In addition,the significant correlation was detected between the husk length and the husk number,while the correlation for other traits were not significant.Also,there were significant differences between different subgroups of the same husk traits.Under the default threshold(P<7.98×10-9)and adjust threshold(P<7.26×10-6),we found 7 and 99 SNPs loci significantly correlated with husk traits.Then,we mined 8 and 99 candidate genes under the above two thresholds.We merely analyzed candidate genes above the default threshold,which were categorized into 4 categories.Among them,the candidate gene belonging to the transcriptional regulatory pathway was GRMZM2G400452,the candidate genes belonging to the cellular transport pathway were GRMZM2G447657 and GRMZM2G056908,the candidate genes belonging to the metabolic pathway were GRMZM2G074331 and GRMZM2G090051,the candidate genes belonging to the signal transduction pathway were GRMZM2G402171,GRMZM2G088974 and GRMZM2G011364.Above all,the husk number and the husk thickness had higher phenotypic plasticity than other husk traits.Hopefully,these two husk traits could were controlled in different environments by the regulation of phenotypic plasticity candidate genes.