杂种优势已广泛应用于玉米育种,在提高玉米产量、品质以及增强抗逆性等方面起到了重要的作用,然而杂种优势的分子机制尚不清楚.植物miRNA主要在转录和转录后水平调节基因的表达.为阐明miRNA是否及如何对玉米雌穗发育杂种优势产生影响,本研究对玉米杂交种郑单958及其亲本自交系(昌7-2和郑58)进行了高通量miRNA测序和降解组测序.取玉米雌穗花序分生组织(IM)发育为成对小穗分生组织(SPM),进而产生小穗分生组织(SM),及小花分生组织(FM)将3个不同时期的雌穗样品用于miRNA建库测序,鉴定出16个miRNA家族中的81个保守miRNA为非加性表达,认为是与雌穗发育杂种优势形成相关的miRNA;3个阶段中分别检测到80.30%、56.06%和48.10%的非加性表达的miRNA被显性或超显性抑制.鉴定出8种新的miRNA,属于7个miRNA家族.通过雌穗降解组测序,发现在郑单958及其亲本自交系中共同检测到的miRNA靶向42个基因的82个转录本.根据测序结果构建了miRNA参与玉米雌穗杂种优势的模型,并推测在雌穗发育早期阶段杂交种雌穗的miRNA的普遍抑制导致其靶基因上调表达,随着发育进程miRNA逐步解除抑制,带来其靶基因表达量的逐步减少,这种miRNA与其靶基因的拮抗关系也许与玉米雌穗发育杂种优势形成有关.%Heterosis has been utilized widely in maize breeding; it plays an important role in increasing yield, improving quality and enhancing stresses resistance. However, the molecular mechanism of heterosis is far from clear. MicroRNAs (miRNAs) act as key regulating factors of gene expression in post-transcriptional level. To investigate whether miRNA-dependent gene regulation is responsible for heterosis during maize ear development, we performed an illumine miRNA deep-sequencing on the most widely-planted elite hybrid Zhengdan 958 and its parental inbred lines (Chang 7-2 and Zheng 58) in China. The ear samples at the developmental stages of inflorescence meristem (IM) producing spikelet pair meristems (SPM), resulting in spikelet meristems (SMs), and floral meristems (FM) were collected for RNA library construction. As a result, 81 conserved miRNAs belonging to 16 miRNA families were identified which were non-additively expressed. At the three stages, 80.30%, 56.06%, and 48.10% of these non-additively expressed miRNAs were repressed ever dominantly or over-dominantly. A total of 82 target transcripts from 42 genes of conserved miRNAs among Zhengdan 958 and its parents were detected via whole genome degradome sequencing. Additionally, eight novel maize miRNAs belonging to seven miRNA families were identified using stringent criteria. Global repression of miRNAs in hybrid ears at the early stage might lead to the up-regulated expressing of their target genes. Moreover, the in-step de-repression of given miRNA family members may be the reason of enhanced repression of their target genes. These results revealed, at least in part, the involvement of maize miRNAs in hybrids leads to higher ear developing vigor compared with its parental lines.
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