Background

Internode elongation is an important agronomic trait in rice that determines culm length, which is related to lodging, panicle exsertion, and biomass. sui4 (shortened uppermost internode 4) mutants show reduced internode length and a dwarf phenotype due to shortened internodes; the uppermost internode is particularly severely affected. The present study was performed to identify the molecular nature and function of the SUI4 gene during internode elongation.

Results

Our previous study showed that the SUI4 gene was mapped to a 1.1-Mb interval on chromosome 7 (Ji et al. 2014). In order to isolate the gene responsible for the sui4 phenotype, genomic DNA resequencing of sui4 mutants and wild-type plants and reciprocal transformation of wild-type and mutant alleles of the putative SUI4 gene was performed. The data revealed that the causative mutation of sui4 was a T to A nucleotide substitution at the microRNA172 binding site of Os07g0235800, and that SUI4 is a new allele of the previously reported gene SUPERNUMERARY BRACT (SNB), which affects flower structure. In order to understand the effect of this mutation on expression of the SUI4/SNB gene, SUI4/SNB native promoter-fuzed GUS transgenics were examined, along with qRT-PCR analysis at various developmental stages. In sui4 mutants, the SUI4/SNB gene was upregulated in the leaves, culms, and panicles, especially when internodes were elongated. In culms, SUI4/SNB was expressed in the nodes and the lower parts of elongating internodes. In order to further explore the molecular nature of SUI4/SNB during internode elongation, RNA-seq and qRT-PCR analysis were performed with RNAs from the culms of sui4 mutants and wild-type plants in the booting stage. The data showed that in sui4 mutants, genes deactivating bioactive gibberellins and cytokinin were upregulated while genes related to cell expansion and cell wall synthesis were downregulated.

Conclusion

In summary, this paper shows that interaction between SUI4/SNB and microRNA172 could determine internode elongation during the reproductive stage in rice plants. Due to a mutation at the microRNA172 binding site in sui4 mutants, the expression of SUI4/SNB was enhanced, which lowered the activities of cell expansion and cell wall synthesis and consequently resulted in shortened internodes.

中文翻译：

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SUPERNUMERARY BRACT（SNB）的microRNA172结合位点的突变抑制了水稻的节间伸长。

背景

节间伸长是决定水稻茎秆长短的重要农艺性状，与倒伏，穗伸长和生物量有关。sui4（缩短的最上层节间4）突变体显示节间长度减小，并且由于节间缩短而导致表型矮化。最上面的节点间受到特别严重的影响。进行本研究以鉴定节间延长期间SUI4基因的分子性质和功能。

结果

我们之前的研究表明，SUI4基因在7号染色体上的定位间隔为1.1 Mb（Ji等，2014）。为了分离负责sui4表型的基因，对sui4突变体和野生型植物进行了基因组DNA重测序，并推定了SUI4基因的野生型和突变等位基因的相互转化。该数据显示，的致病突变sui4是一件T到在microRNA172结合的位点的核苷酸的取代Os07g0235800，并且SUI4是先前报道的基因S的一个新的等位基因UPERNUMERARY苞片（SNB），影响花的结构。为了了解此突变对SUI4 / SNB基因表达的影响，我们对SUI4 / SNB天然启动子融合的GUS转基因进行了研究，并在各个发育阶段进行了qRT-PCR分析。在sui4突变体中，SUI4 / SNB基因在叶，茎和穗中被上调，尤其是当节间延长时。在茎中，SUI4 / SNB在节间和延长节间的下部表达。为了进一步探究SUI4 / SNB在节间延伸过程中的分子性质，使用了来自Sul4 / SNB茎的RNA进行了RNA-seq和qRT-PCR分析。sui4突变体和野生型植物处于启动阶段。数据显示，在sui4突变体中，使生物活性赤霉素和细胞分裂素失活的基因被上调，而与细胞扩增和细胞壁合成相关的基因被下调。

结论

总之，本文表明，SUI4 / SNB与microRNA172之间的相互作用可以决定水稻生殖阶段的节间伸长。由于sui4突变体中microRNA172结合位点的突变，SUI4 / SNB的表达增强，这降低了细胞扩增和细胞壁合成的活性，因此导致节间缩短。