Germplasm Evaluation Of Maize Germination And Seedling Emergence Characteristics And Its Relationship With Aquaporins

High-vigour seeds that exhibit rapid and uniform seed germination and vigorous field seedling emergence are the basis of high crop yields.Water is a key factor for seed germination and seedling emergence.Plant aquaporins（AQPs）-mediated water transmembrane transport may be involved in the regulation of seed germination and seedling emergence,but there are few related studies in maize.Maize germplasm resources are abundant,and the germplasm evaluation of maize germination and seedling characteristics are of great significance to maize germplasm improvement and utilization.In this study,the maize natural population（including368 inbred lines）was used as the material,and the phenotype of maize seed germination and seedling emergencewas analyzed by standard germination experiments.And the cluster analysis and germplasm evaluation of maize population based on germination and emergence characteristics was performed.Meanwhile,the relationship between maize aquaporins（ZmAQPs）and germination characteristics was clarified,and the natural variation of related ZmAQPs was analyzed.This study provided important genetic resource and germplasm resources for maize germplasm improvement and utilization.The main findings are as follows:1.The phenotypes of the germination and seedling characteristics of maize natural populations were identified and analyzed.The seedling length,mesocotyl length,dry weight per plant and vigor index were normally distributed.The variation coefficient of the length of mesocotyl and coleoptile,germination potential and vigor index was the largest,which were23.65%,24.33%,35.03% and 24.66%,respectively.The results of phenotypic analysis showed that the phenotypic traits were quantitative traits,and the variation coefficient of the related traits was large,indicating that the maize population was rich in germplasm resources.According to cluster analysis of the characteristics of germination and emergence,we divided the population materials into three categories,namely,inbred lines with excellent,medium and poor characteristics of germination and seedling,including 183,106,and 45 accessions,respectively.At the same time,according to the analysis of the genetic structure of the population by SNP markers,the population was divided into 8 populations,and the P1 had the highest proportion of materials with excellent seedling characteristics,accounting for 87.5%.The proportion of materials with poor seedling characteristics in the P5 was the highest,accounting for 47.37%.The inbred lines with excellent germination and emergence characteristics exhibit longer length of shoot（Sh L）and mesocotyl（Me L）,higher germination energy（GE）,germination index（GI）,seeding germination rate（SER）and vigor index（VI）.The dry weight（DW）,SER,GE,GI and VI,were relatively lower in inbred lines with poor characteristics of germination and seedling emergence.2.The correlation analysis of seed emergence time and seed composition showed that DW and SER were significantly positively correlated with hundred grain weight（HGW）,the absolute content of protein（ACP）,the absolute content of oil（ACO）,and the absolute content of oil（ACS）,and Sh L was significantly positively correlated with HGW and the relative content of protein（RCP）.VI was significantly positively correlated with HGW,ACP,ACO,ACS.3.The gene expression analysis of multi-tissues samples showed that ZmAQPs had distinct spatiotemporal and tissue-specific expression profiles during seed germination and early seedling development.Most ZmPIPs and ZmTIPs showed the highest expression in the rapid elongation zones of roots mesocotyl of seedlings.Meanwhile,almost all the ZmAQPs examined showed relatively higher expression levels in roots than that of the other tissues.Further,we explored the differential expression analysis during seedling emergence in different inbred lines.The expression levels of ZmPIP1-1,ZmPIP1-2,ZmPIP1-5,ZmPIP2-3,ZmPIP2-4,ZmPIP2-6,ZmTIP1-1 and ZmTIP2-1 in materials with fast seedling emergence were significantly higher than those in slow-emergence materials.Through the correlation analysis of the emergence characteristics of inbred lines and the expression levesl of ZmAQPs,the expression levels of ZmPIP1-5,ZmPIP2-6,ZmTIP1-1,ZmTIP1-2,ZmTIP2-1 had a certain positive correlation with the emergence characteristics.We speculate that ZmAQPs are involved in the regulation of maize germination and seedling emergence.4.We further conducted SNP analysis in the region of genes of ZmPIP2-6,ZmTIP1-1 and ZmTIP2-1 among maize population,and haplotype-mining analysis.According to the genetic structure of maize poplation and the cluster analysis of germination and emergence characteristics,the haplotype of excellent type accounted for the highest proportion in P1 population.Among them,Hap2,Hap5,Hap8,Hap10,Hap13,Hap42,Hap77,and Hap98 of ZmPIP2-6 are excellent haplotypes,Hap2,Hap11,Hap18,and Hap21 of ZmTIP1-1 are excellent haplotypes,and Hap5,Hap7,Hap9,Hap23,Hap91,Hap92,Hap140 of ZmTIP2-1 are excellent haplotypes.