Ji Hyeonso, Han Chang-Deok, Lee Gang-Seob, Jung Ki-Hong, Kang Do-Yu, Oh Jun, Oh Hyoja, Cheon Kyeong-Seong, Kim Song Lim, Choi Inchan, Baek Jeongho, Kim Kyung-Hwan
Department of Agricultural Biotechnology, National Institute of Agricultural Sciences (NAS), Jeonju, 54874, South Korea.
Division of Applied Life Science (BK21 Program), Plant Molecular Biology and Biotechnology Research Center (PMBBRC), Gyeongsang National University, Jinju, 52828, South Korea.
Rice (N Y). 2019 Aug 9;12(1):62. doi: 10.1186/s12284-019-0324-8.
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.
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.
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.
节间伸长是水稻的一个重要农艺性状，它决定茎秆长度，而茎秆长度与倒伏、穗抽出度和生物量相关。sui4（最上部节间缩短4）突变体由于节间缩短而表现出节间长度减小和矮化表型；最上部节间受到的影响尤为严重。本研究旨在鉴定节间伸长过程中SUI4基因的分子本质和功能。
我们之前的研究表明，SUI4基因被定位到第7号染色体上一个1.1-Mb的区间（Ji等人，2014年）。为了分离导致sui4表型的基因，对sui4突变体和野生型植株进行了基因组DNA重测序，并对推定的SUI4基因的野生型和突变等位基因进行了相互转化。数据显示，sui4的致病突变是Os07g0235800的microRNA172结合位点处的一个T到A的核苷酸替换，并且SUI4是先前报道的影响花结构的基因SUPERNUMERARY BRACT（SNB）的一个新等位基因。为了了解该突变对SUI4/SNB基因表达的影响，检测了SUI4/SNB原生启动子融合GUS转基因植株，并在不同发育阶段进行了qRT-PCR分析。在sui4突变体中，SUI4/SNB基因在叶片、茎秆和穗中上调表达，尤其是在节间伸长时。在茎秆中，SUI4/SNB在节和伸长节间的下部表达。为了进一步探究节间伸长过程中SUI4/SNB的分子本质，在孕穗期对sui4突变体和野生型植株的茎秆RNA进行了RNA-seq和qRT-PCR分析。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上调，而与细胞扩张和细胞壁合成相关的基因下调。
总之，本文表明SUI4/SNB与microRNA172之间的相互作用可以决定水稻植株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，这降低了细胞扩张和细胞壁合成的活性，从而导致节间缩短。
