Mining Key Genes Involved In The Regulation Of Ligular Region Development And Leaf Angle (LA) Formation In Maize

Maize(Zea mays)is one of the most important economic crops worldwide.Leaf angle(LA),the inclination between the leaf blade and the stem,is one of the important agronomic traits affecting maize architecture and yield.The smaller LA is beneficial to reduce the canopy interception rate of light,raise the group utilization of solar energy and the group planting density,thus to improve the yield.Consequently,compact plant architecture is an important goal of maize breeding.The ligular region,a connection hub(consists of the ligule and the auricle)in the middle of the maize leaf blade and sheath,is the crucial part of regluating LA.Revealing the molecular mechanism controlling the ligular region development will be conducive to further reveal the mechanism regulating the size of LA.Thus,this study analyzed the cellular and transcriptional changes in early,middle and late stage ligular region of B73(non-upright inbred with wide LA)and 986(upright inbred with narrow LA),mined key genes involved in the regulation of LA,provided theoretical basis and candidate genes for optimizating maize architecture and improving the yield.The main results are as follows:(1)We detected both LA and ligular region angle(LRA)in 113 inbred lines with differences in LA.The positive Pearson correlation coefficient between LA and LRA further indicated an important role of maize ligular region in leaf declination.(2)The cellular events associated with the early,middle and late stage ligular region in both B73 and 986 are investigated by scanning electron microscope(SEM).The early stage ligular region is the preligule band(PLB),at middle stage ligular region upper part began to widen and LRA began to form,the leaf has been mature at late stage.Early in ligular region development,cell division was dominant.It is at middle stage that the main differences between B73 and 986 occur: the cells in B73 are more inclined to division,while the cells in986 are more inclined to elongation.At late stage,B73 and 986 showed little difference in cell length-width-ratio.Thus,it is the more cell numbers that are responsible for larger ligular region in B73 than in 986.(3)Analysis the RNA-seq data set of transcripts of ligular region tissues from early,middleand late developmental stages in B73 and 986.In total,21582 and 22099 genes were detected expressing in B73 and 986,respectively,5996 and 4715 genes were identified to be differentially expressed in at least one stage in B73 and 986,respectively.2797 differentially expressed genes(DEGs)appeared to be differentially expressed in both B73 and 986.The distribution of these genes in B73 and 986 has strong similarity,we hypothesized that the regulatory mechanism of ligular region development in B73 and 986 may be consistent.(4)We then used MapMan annotation to assign 2797 DEGs to functional categories.Early in ligular region development,transcripts involved in DNA and protein synthesis,cell cycle,cell organization and signaling were enriched.At middle and late stages,most genes involved in cell wall modification,secondary metabolism and photosynthesis were peak expressed.At middle stage that the main differences occur between B73 and 986,the genes involved in cell division regulation were higher expressed in B73,while the genes involved in cell elongation regulation were higher expressed in 986.Interestingly,transcripts involved in hormone metabolism,signaling and responses,as well as several transcription factors are expressed in a stage-specific manner.(5)By using F6 generation of recombinant inbred lines derived from crosses between Su115×986 to detect the SNP-arrays,we identified two QTLs responsible for leaf angle in chromosome 5.Combined previous GWAS identified SNPs with RNA-seq gene expression,we finally mined 6 key genes that may be important for LA regulation.In conclusion,according to reveal the cytological basis and gene expression pattern of ligular region development and LA formation in maize,we finally mined key genes that regulating LA formation.Further functional analysis of them will provide a rich resource for maize genetics and breeding.