Different Molecular Responses Of Ear Leaves From Different Maize Genotypes During The Grain-filling Stage To High Plant Density

Maize is one of the most widely cultivated cereal crops in the world.It provides essential staple food for humans,the main feed for livestock and poultry,and an important raw material for industrial and biofuels.In production,in order to increase the yield of maize,growers usually use the method of increasing planting density.However,when the planting density is increased,the light,water and nutrient supply per plant are reduced,resulting in reduced photosynthesis and inhibited plant development,which is prone to lodging or serious diseases and insect pests,which in turn leads to a decline in population yield.Therefore,it is of great significance to explore the tolerance mechanism of maize.In this study,maize dense genotype Xianyu 335 and non-tolerant genotype KD1173 were selected as materials and planted at low density(52500 plants / hm2)and high density(75000 plants / hm2).The RNA was extracted from panicle leaves at 40 days during the filling stage,and the second-generation RNA-seq technology was used to sequence the transcriptome.First,the two genotypes were compared for gene expression differences at high and low densities;then,the two genotypes were compared.The gene expression difference between high and low density,the key genes corresponding to the density of maize were screened to provide molecular basis for maize density tolerance breeding.The main results are as follows:(1)Sequencing of 4 ear-leaf samples from XY335 and KD1173 yielded a total of617,795,068 clean reads.These sequences were compared with the maize B73 reference genome sequence,with an average alignment rate of 79%,of which approximately 67% are expressed genes.(2)There are total 14829 differentially expressed genes were identified from the ear leaves of xy335 and kd1173 at two densities.Among them,XY335 uses low density as a control to identify 825 differentially expressed genes from high-density leaves,There are 221up-regulated and 604 down-regulated genes;KD1173 uses low-density as a control to identify differentially expressed genes from high-density.There are 174 genes in total,including 99up-regulated and 75 down-regulated genes;at low density,there are 7478 differentially expressed genes between XY335 and KD1173,of which 4119 are up-regulated and 3359 are down-regulated;At high density,There were 6352 differentially expressed genes between KD1173 and XY335,of which 3255 genes were up-regulated and 3097 genes were down-regulated.Through GO and Pathway significant enrichment analysis,it was found that these differentially expressed genes were mainly concentrated in carbohydrate metabolism,photosynthesis,substance transport,heat shock protein binding protein,sucrose transmembrane transporter,r RNA binding protein and so on.(3)A total of 908 differentially expressed transcription factor genes were identified from panicle leaves.These genes involved 47 families,most of which were distributed in the ERF,MYB and NAC families.Among them,61 transcription factor genes were identified from XY335,and 7 transcription factor genes were identified from KD1173.(4)Comprehensive analysis of the expression of hormone-related genes in the ear leaves of maize showed that the expression levels of two genes encoding ACO(GRMZM2G126732,GRMZM2G052422)in maize XY335 were down-regulated as the density increased.The gene encoding the ethylene receptor(GRMZM2G066449)in the comparison of different genotypes with the increase of planting density,the expression level was down-regulated and significantly different.The key enzyme genes(GRMZM2G407181,GRMZM2G127139,GRMZM2G014392)involved in abscisic acid synthesis showed an upward trend.Comparing the differentially expressed genes of different tolerance genotypes,two genes related to gibberellin synthesis(GRMZM2G049418,GRMZM2G036340)were identified in Xianyu335,and the expression was up-regulated.