Hebei Sub-center of Chinese National Maize Improvement Center, North China Key Laboratory for Crop Germplasm Resource of Education Ministry, College of Agronomy, State Key Laboratory of North China Crop Improvement and Regulation, Hebei Agricultural University, Baoding 071000, PR China.
Beijing Agro-Biotechnology Research Center, Beijing Academy of Agricultural and Forestry Science, Beijing 100097, PR China.
Gene. 2020 Oct 5;757:144928. doi: 10.1016/j.gene.2020.144928. Epub 2020 Jul 2.
Tassel branch number (TBN) is the principal component of tassel inflorescence architecture in the maize plant. TBN is believed to be controlled by a set of quantitative trait loci (QTLs). However, it is necessary to identify and genetically evaluate these QTLs before the TBN can be improved upon using a molecular breeding approach. Therefore, in this study, we developed the chromosome segment introgression line (CSIL) TBN1 with the Zong31 (Z31) background and a higher TBN, and then we utilized the CSIL-TBN1-derived populations and identified a major QTL, qTBN6a, by linkage analysis. Fine mapping of the qTBN6a QTL was validated using a set of sub-CSILs and located in a 240-kb genomic region (Bin6.07) in B73RefGen_v4. One allele included in the introgression fragment had a positive effect, noticeably increasing the TBN and demonstrating the potential to improve the TBN of Z31. Afterward, in the qTBN6a interval, gene expression, sequence alignment, functional analysis, and the analysis of motifs in the 5' UTR suggested that candidate genes of qTBN6a are important functional genes at the early stage of immature infected tassel development. Among these candidate genes, a long W22::Mu-insertion/deletion in exon one and an 11-bp insertion/deletion in the promoter region may affect the variation of the qTBN6a QTL observed between Z31 and TBN1. In addition, the candidate genes of qTBN6a were found to encode a pentatricopeptide repeat (PPR)-containing protein and a histone deacetylase (HDA), which are known to be closely associated with RNA editing and stability and chromatin state activity for the transcription of gene expression, respectively. Finally, a model of qTBN6a based on the synergistic regulation of PPR and HDA for the maintenance of inflorescence meristem (IM) identity and its differentiation to the branch meristem (BM) in TBN1 was suggested. Collectively, our results provide an available locus for the molecular improvement of TBN and the isolation of functional genes underlying this QTL.
穗分支数（TBN）是玉米植物穗状花序结构的主要组成部分。TBN 被认为受一组数量性状基因座（QTL）控制。然而，在使用分子育种方法改进 TBN 之前，有必要识别和遗传评估这些 QTL。因此，在这项研究中，我们以 Zong31（Z31）为背景开发了具有更高 TBN 的染色体片段导入系（CSIL）TBN1，然后利用 CSIL-TBN1 衍生群体，通过连锁分析鉴定到一个主要的 QTL，qTBN6a。利用一组亚 CSIL 对 qTBN6a QTL 进行精细定位，并将其定位在 B73RefGen_v4 的 240-kb 基因组区域（Bin6.07）中。导入片段中包含的一个等位基因具有正效应，明显增加了 TBN，表现出改善 Z31 TBN 的潜力。之后，在 qTBN6a 区间，基因表达、序列比对、功能分析以及 5'UTR 中的基序分析表明，qTBN6a 的候选基因是未成熟感染小穗发育早期的重要功能基因。在这些候选基因中，一个长 W22::Mu-插入/缺失在一个外显子中，以及一个 11-bp 的插入/缺失在启动子区域可能会影响在 Z31 和 TBN1 之间观察到的 qTBN6a QTL 的变化。此外，qTBN6a 的候选基因编码一个五肽重复（PPR）含蛋白和一个组蛋白去乙酰化酶（HDA），它们分别与 RNA 编辑和稳定性以及组蛋白状态活性密切相关，从而影响基因表达的转录。最后，提出了一个基于 PPR 和 HDA 协同调控的 qTBN6a 模型，用于维持花序分生组织（IM）的身份及其向 TBN1 分支分生组织（BM）的分化。总的来说，我们的研究结果为 TBN 的分子改良和该 QTL 下功能基因的分离提供了一个可用的位点。
