| Plant morphology improvement is an important approach for high yield breeding of maize and tassel branching is one of the important components of plant morphology,the number of tassel branches directly affects the light interception of maize leaves and to a certain extent determines the tolerance of dense planting,thus affecting the yield.The discovery of genes controlling tassel branch number in maize at the molecular level will provide new gene resources for tassel improvement by biotechnology and lay a foundation for molecular markerassisted breeding of tassel branch.In this study,two F4 families were constructed using LX1 and LX2,high-generation sister lines of maize with significant differences in tassel branch number,as parents to verify ub4 gene,which was finely mapped by our research group in the early stage.Further,the breeding effect of ub4 was evaluated in four F2 and BCi populations of LX1 and classical maize inbred lines Huangzaosi,Mo17 and B73,which are widely used in breeding.At the same time,the endogenous hormone levels of LX1 and LX2 tassel differentiation and development were compared to explore the physiological mechanism of tassel branching development in maize.In addition,the expression profile of ub4 candidate gene Zm00001d038546 was constructed using B73 as material,in order to determine the expression period and location of candidate gene.The main results of this study are as follows:1.LX1 and LX2 were planted at the densities of 45,000 plants/hm2,67,500 plants/hm2,90,000 plants/hm2,112500 plants/hm2 and 135,000 plants/hm2 in Sanya,Hainan and Shenyang,Liaoning,respectively.It was found that LX1 and LX2 had almost no variation in tassel branch number under 10 conditions,indicating that the genetic information of tassel branch carried by LX1 and LX2 was stable and suitable for breeding.Using two F4 populations formed by continuous self-cross selection of exchanged single plants in the fine localization interval of ub4 in F2 populations mated with LX1 and LX2 as parents,the genotyping results of the coisolated marker of ub4 candidate gene Zm00001d038546 were highly consistent with the tassel branch number phenotype,which further verified ub4.2.Genotypic identification and phenotypic investigation were carried out on four F2 and BCi populations of LX1,HZ4,Mo17 and B73.It was found that the tassel branch numbers of the populations were in the following order:average tassel branch numbers of individuals ub4 genotype with LX2>ub4 heterozygotic status>ub4 genotype with LX2.One allele from ub4 decreased the number of tassel branches of HZ4,Mo17 and B73 by 3.9,2.7 and 3.5,respectively.ub4 could fine-tune the tassel branch number,and LX1 could be used as an important germplasm in tassel branch number breeding.Functional markers indel546,snym010 and snym188 were also provided for molecular marker-assisted breeding of tassel branch number in maize.3.qRT-PCR was used to detect the expression of Zm00001d038546 gene in different tissues and developmental stages of B73,and the spatio-temporal expression pattern of Zm00001d038546 was analyzed.The results showed that Zm00001d038546 was widely involved in the growth and development of maize.It was highly expressed in maize tassel,silk,root and leaf,low in stem and endosperm,and almost no expression in embryo.Meanwhile,the expression of Zm00001d038546 in the tassel development process of maize showed that the expression level of Zm00001d038546 was low in the growth cone extension period at the beginning of maize tassel development.The expression level increased in the later differentiation process,and was highest at the early stage of tassel differentiation,and remained high until the completion of tassel differentiation.Our previous study found that the early stage of tassel differentiation was the key stage for tassel differentiation in LX1 and LX2 materials.It is speculated that Zm00001d038546 may be involved in the growth and development of tassel branch of maize.4.By analyzing the endogenous hormone content of LX1 and LX2 tassels,it was found that:The contents of indole-3-acetic acid(IAA),tryptamine(TA),an important precursor of auxin synthesis pathway,and indole-3-formaldehyde(ICA),an oxidation product of auxin oxidative decomposition pathway in LX1 were significantly higher than those in LX2.The content of 5-deoxyachitol(5DS),the first active product of achitolactone biosynthesis pathway,in LX2 was 54.08%higher than that in LX1,while the contents of cytokinin(CTK),gibberellin(GA),ethylene(ACC)and abscisic acid(ABA)were not significantly different between LX2 and LX1.Cluster analysis also showed that the difference of hormone content between the two materials mainly focused on auxin and soligolactone.These results suggest that auxin and strigolactone may be involved in the differential regulation of tassel branch number in maize. |
