Studies On The Molecular Genetic Mechanism Of Plant Architecture Traits In Maize (zea Mays L.)

Maize is a not only important cereal crop but alse important forage, economic and energy crop. High yield is a most important aim that modern maize breeders pursue today. Maize plant-type breeding with the aim by improving plant-type, strengthening resistance high-density adversity, and improving group photosynthetic efficiency is a main approache to achieve high yield of corn. Therefore, researches related to the characters of corn plant molecular genetic mechanism has the important theoretical and practical significance to not only promote maize resistance high-density breeding and molecular marker assisted selection technology development but aslo analyze maize plant traits molecular biology mechanism.In this study, maize architecture traits QTL as the main research object carry out research as following four steps. Firstly, a set of F2:3 families derived from a compact and expanded maize inbred line cross were developed.a set of 229 F2:3 families derived from compact and spread-out inbred line cross was evaluated for three environments. Genetic linkage maps with 222 SSR markers were constructed using Mapmaker version 3.0. Were detected for the six measured morphological traits using composite interval mapping (CIM). The performinance data of plant architecture traits in the F2:3 families were used for QTL mapping and analysis to genetic effect. Secondly, the genetic linkage maps with 352 SSR markers integrated using the two sets of genotypes data from F2 population of different parents and the performinance data of plant architecture traits from the two populations evaluated in three environments were used for further QTL mapping and confirmation by analysis technique of multiple population joint QTL and the chromosomal regions that main effect QTL with the traits concentrated were identified. In addition, the cadidate genes of QTL located on chromosome regions were speculated using comparative genomics and bioinformatics. Thirdly, our research objective concentrated on the major effect QTL qLA1-1 with leaf angle by preliminary results of QTL mapping. The near-isogenic line (NIL) of qLA1-1 were successfully constructed using repeatedly backcross and molecular marker assisted selection. qLA1-1 were confirmed by BC3F2:3 families. Fine mapping of qLA1-1 by the BC3F2 segregation population and the latest molecular marker developed shortened the distance of QTL region that were limited in 0.75 Mb scope. Finally, the candidate gene speculated in the scope of major effect QTL was cloned through homology-based cloning. ZmTAC1 was successfully cloned that the gene was high homologous to OsTAC1 with rice leaf angle. A CAPs marker was developed on the basis of the differences of parents DNA sequences. As the function marker of the gene, the performinance data of leaf angle were again used for QTL mapping. In addition, the DNA sequences that 31 inbred lines had difference of leaf angle were cloned and analysed. The relationship of ZmTAC1 and leaf angle was identified. The main results obtained in this research were concluded as follow:1. The linkage map of 222 SSR markers constructed using F2 population of Yu82×Shen137 consisted of all ten maize chromosomes allocated to ten linkage groups, spanning a total length of 1864.7 cM with an average marker interval of 8.40 cM. QTL for plant architecture traits were mapped using a set of 229 F2:3 families derived from the cross between compact and expanded inbred lines, evaluated in three environments. Twenty-five QTL were detected in total on the rest 8 chromosomes besides chromosome 6 and 8. 3 QTL of leaf angle were located, 5 QTL of leaf orientation value were detected, 3 QTL of leaf length were detected, 4 QTL of blade width were detected, 3 QTL of plant height were located, and 7 QTL of ear height were located. Two key genome regions controlling leaf angle and leaf orientation were identified from our study. The QTL between umc1166 and umc2226 in the 1.02 region of chromosome 1 explained 20.4% of the phenotypic variance and another QTL between umc1166 and umc2226 in the 5.04-5.05 region of chromosome 5 explained 9.7% of the phenotypic variance. two QTL associated with decreased leaf angle and increased leaf orientation value were contributed by Yu82.2. The linkage map of 333 SSR markers, 3 CAPs markers developed, and 16 candidate genes were integrated using two F2 population3 of Yu82×Shen137 and Yu82×Yu87-1, spanning a total length of 1766.4 cM with an average marker interval of 5.0 cM. 33 QTL were detected for leaf angle, leaf orientation value, leag length, and blade width using MCQTL 4.0. Seven QTL for leaf angle were located on chromosome 1, 2, 3, 5, 7, and 8 with individual effects ranging from 7.3% to 19.0%. 11 QTL for leaf orientation value were detected on chromosome 1, 2, 3, 4, 5, 7, 8, and 9 with individual effects ranging from 5.03% to 23.2%. 7 QTL associated with leaf length were located on chromosome 3, 5, 7, and 1 with individual effects rangingfrom 7.14% to 20.6%. 8 QTL of leaf width were detected on chromosome 1, 3, 4, 7, 8, and 9 with individual effects ranging from 4.86% to 20.4%. Two key genome regions(ZmLAR1and ZmLAR2)controlling leaf architecture traits were identified from our study. ZmLAR1 were between umc1608 and umc1674 on chromosome 3 with individual effect of four traits ranging from 9.26% to 20.4% and ZmLAR2 were between umc1380 and umc1936 on chromosome 7 with individual effect of the traits ranging from 6.8% to 14.3%. Moreover, 3 genome regions of leaf angle, a genome region of leaf length, and 1 genome region of leaf width were identified. All these regions encompass candidate genes DWARF4, TAC1, LIC, YABBY15, ligueless1and ligueless2 for leaf angle, lng1 for leaf length, and NAL7 for leaf width.3. According to the results of QTL mapping, QTL qLA1-1-NIL in bin 1.02 of chromosome 1 for leaf angle was constructed by more once backcrosses and"Double Card"."One Card"was RRGB greater than 95% and"Two Card"was leaf angle lesser than 12.5o. qLA1-1 was idengtified again using BC3F2:3famalies and that the NIL had controled leaf angle for single locus segregation. 43 SSR markers were developed in the target region. 9 SSR markers had polymorphism strong and clear banding. qLA1-1 was defined by BC3F2 population between LA25 and bnlg1484, spanning a total length of 0.75 Mb.4. ZmTAC gene for leaf angle was cloned by homology-based cloning in maize inbred lines Yu82 and Shen137, a predicated 792-bp open reading frame was detected in the cloned sequence, which encoded 263 amino acids. The protein sequence was 91% homology to rice TAC1. The difference in the inbred lines which a single DNA letter change in the 5'- untranslated region(UTR) caused the difference in expression level of mRNA. Real-time PCR analysis revealed that ZmTAC1 was expressed superlatively in leaf sheath and pulvinus, secondly in leaf and stem apex, and expressioned from 4-leaf stage, with the peak at 9-11 leaf stage, the expression decreased gradually from 11-leaf stage. Yu82 was lower than Shen137 in expression. The sequence of Yu82(CTCCT) in 5'- UTR was always associated with 13 compact plant architecture inbred lines and the sequence of Shen137(CCCCT) in 5'- UTR was always associated with 18 expended plant architecture inbred lines. ZmTAC1 was defined in the region of qLA1-2 by the CAPs developed and the F2:3 families of Yu82×Shen137.