Mechanism Of Uniconazole And 5-aminolevulinic Acid Regulating Female Ear Formation In Maize

Female ear,an important reproductive organ of maize,whose morphology directly affects the yield formation,and the silking stage is the critical period for maize morphological formation.In recent years,plant growth regulators(PGRs)have attracted much attention by having been widely used in crops,vegetable crops and garden plants to improve plant morphogenesis and increase yield.In this study,two types PGRs,delayed uniconazole(S3307)and promotive 5-aminolevulinic acid(ALA),were sprayed on the leaves of different genotype maize varieties Xianyu335 and Nendan18 at 12-leaf stage.The regulatory effects of the two types PGRs on maize female ear were discussed from the aspects of yield,ear morphology,microstructure,physiologica-biochemical indexes and transcriptome analysis.The main results and conclusions are as follows:1.Two types of regulators treatment increased the yield of both two varieties in2020 and 2021.With S3307 treatment,grain yield of Xianyu335 and Nendan18 were increased by 8.36%～11.85% and 6.79%～11.95% respectively compared to control test.After ALA treatment,grain yield of Xianyu335 and Nendan18 were increased by 11.35%～13.91% and 8.3%～12.83% respectively.The effects of two types of regulators on yield components are not the same.The number of rows per ear and grain weight of both varieties were significantly increased after S3307 treatment,while the grain number per row and grain weight of both varieties were significantly increased after ALA treatment.2.Two types of regulators application could regulate the morphology and microstructure of the female ear of both maize varieties,but the regulation effects were different.After treatment with S3307,the length of female ear of Xianyu 335 and Nendian18 decreased from tasseling stage to two weeks after silking stage,while the length of female ear increased significantly after ALA treatment.The up-regulation of S3307 treatment on female ear and the diameter of cobs of two varieties was better than that of ALA treatment.Meanwhile,the two regulators increased the female ear,cob,dry and fresh grain weight of both varieties to varying degrees.Microstructure observation showed that S3307 treatment increased the cob cross-sectional area and cell wall thickness of both varieties,while ALA treatment had no effect on the cob cross-sectional area of both varieties,and the thickness of the cell wall had a decreasing trend.3.The young ear of Nendan 18 was taken for transcriptional determination during silking stage,and the differential genes(DEGs)after S3307 treatment were mainly enriched in phenylpropanoid biosynthesis,plant hormone signal transduction,flavonoid biosynthesis,carbon fixation and so on.GO functional analysis showed that the genes of LRR and PERK protein,which are related to cell division,were down-regulated,while the key genes of cell wall synthesis,NAC and MYB,were up-regulated.After ALA treatment,the DEGs were mainly enriched in plant hormone signal transduction,starch and sucrose metabolism and so on.GO functional analysis showed that the expression of cell elongation related gene COBL was up-regulated,and the cell wall modification related genes xylan glycosylhydrolase gene,chitinase gene,endonuclease gene and expandin gene were up-regulated.4.The regulation of endogenous hormones in maize female ear by two types of regulators was different.S3307 treatment down-regulated the endogenous IAA and GA content of female ear,and up-regulated the endogenous ABA content;However,ALA treatment up-regulated the content of endogenous IAA and GA,and down-regulated the content of endogenous ABA;At the same time,both regulators up-regulated the endogenous ZR content.The correlation analysis between female ear morphology and endogenous hormones showed that the contents of endogenous hormones IAA and GA were positively correlated with the length of female ear,while the contents of ABA were negatively correlated with the length of female ear;The endogenous ZR content was positively correlated with female ear diameter;The contents of endogenous GA and ZR were positively correlated with fresh and dry weight of female ear.Among them,the regulation effect of Nendan18 treatment group was more significant than that of Xianyu 335 treatment group.Function analysis of key DEGs in plant hormone signal transduction pathway showed that S3307 treatment down-regulated the expression of response protein genes(IAA and ARF)for IAA synthesis,and up-regulated the expression of Della protein,an inhibitor of GA synthesis;ALA treatment up-regulated the expression of response protein gene(SAUR)for IAA synthesis and down-regulated the expression of repressor gene(AUX/IAA),up-regulated the JAZ expression of JA negative regulator,and up-regulated the expression of SA receptor protein NPR1 gene and transcription factor TGA.5.The two types of regulators have different effects on the regulation of carbohydrate in maize female ear.S3307 treatment increased the content of structural carbohydrate cellulose,hemicellulose and lignin in female ear.Function analysis of key DEGs in phenylpropanoid biosynthesis pathway found that 38 DEGs were up-regulated,and these genes were key genes for lignin synthesis,which could effectively promote lignin synthesis.Function analysis of key DEGs in flavonoid biosynthesis pathway showed that there were 7 genes up-regulated,which could effectively promote flavonoid synthesis.However,ALA treatment had no significant effect on regulating the content of structural carbohydrate cellulose,hemicellulose and lignin in female ear,and there was a downward trend in several periods.Both types of regulators could increase the contents of non-structural carbohydrate starch,sucrose and soluble sugar in female ear to varying degrees.The functional analysis of DEGs in starch and sucrose biosynthesis pathway showed that there were 2 genes related to sucrose hydrolysis and 3 genes related to glucose synthesis in maize female ear after S3307 treatment;The regulation effect of ALA treatment was more significant than that of S3307 treatment,including 4 genes related to sucrose hydrolysis,7 genes related to glucose synthesis and 9 genes related to glucose dimer trehalose synthesis.Thus it can be seen that S3307 and ALA have obvious regulation on the starch and sucrose metabolism pathway in female ear of maize,promote the accumulation of carbohydrates in female ear,and provide more substrates for its formation.