水稻的花器官特征主要由A、B、C、E四类基因决定，它们大多编码MADS-box转录因子。然而，在花发育过程中，对于这些基因的表达如何被调控的研究很少。本研究报道了一个名为SUPER WOMAN 2（SPW2）的基因，该基因在水稻的小穗/小花发育过程中通过调控雌蕊特征基因OsMADS3、OsMADS13、OsMADS58和DL的表达发挥重要作用。SPW2突变导致小穗内的护颖、外稃、内稃、浆片和雄蕊中出现异位的柱头/子房状组织。通过图位克隆，我们揭示了SPW2编码一个植物特有的类EMF1蛋白，该蛋白是PRC2复合物的重要组成部分，并介导H3K27me3修饰。表达分析显示，SPW2突变导致OsMADS3、OsMADS13、OsMADS58和DL在小穗的非雌蕊器官中异位表达。此外，ChIP-qPCR结果显示这些基因在染色质上的H3K27me3修饰水平显著降低。因此，我们的研究结果表明SPW2通过参与H3K27me3介导的雌蕊特征基因表观遗传沉默，进而调控它们在水稻小穗的非雌蕊器官中的表达。这项研究拓宽了我们对于SPW2通过表观遗传调控花器官特征基因的分子机制的认识。

   Leaves play a key role in photosynthesis in rice plants. The premature senescence of such plants directly reduces the accumulation of photosynthetic products and also affects yield and grain quality significantly and negatively. A novel premature senescence mutant, mps1 (mid-late stage premature senescence 1), was identified from a mutant library consisting of ethyl methane sulfonate (EMS) induced descendants of Jinhui 10, an elite indica restorer line of rice. The mutant allele, mps1, caused no phenotypic differences from the wild type (WT), Jinhui 10, but drove the leaves to turn yellow when mutant plants grew to the tillering stage, and accelerated leaf senescence from the filling stage to final maturation. We characterized the agronomic traits, content of photosynthetic pigments and photosynthetic efficiency of mps1 and WT, and fine-mapped MPS1. The results showed that the MPS1-drove premature phenotype appeared initially on the leaf tips at the late tillering stage and extended to the middle of leaves during the maturing stage. Compared to the WT, significant differences were observed among traits of the number of grains per panicle (–31.7%) and effective number of grains per panicle (–38.5%) of mps1 individuals. Chlorophyll contents among the first leaf from the top (Top 1st), the second leaf from the top (Top 2nd) and the third leaf from the top (Top 3rd) of mps1 were significantly lower than those of WT (P<0.05), and the levels of photosynthetic efficiency from Top 1st to the forth leaf from the top (Top 4th) of mps1 were significantly lower than those of WT (P<0.01). Results from the genetic analysis indicated that the premature senescence of mps1 is controlled by a recessive nuclear gene, and this locus, MPS1 is located in a 37.4-kb physical interval between the markers Indel145 and Indel149 on chromosome 6. Genomic annotation suggested eight open reading frames (ORFs) within this physical region. All of these results will provide informative references for the further researches involving functional analyses and molecular mechanism exploring of MPS1 in rice.

    The nuclear-encoded light-harvesting chlorophyll a/b-binding proteins (LHCPs) are specifically translocated from the stroma into the thylakoid membrane through the chloroplast signal recognition particle (cpSRP) pathway. The cpSRP is composed of a cpSRP43 protein and a cpSRP54 protein, and it forms a soluble transit complex with LHCP in the chloroplast stroma. Here, we identified the YGL9 gene that is predicted to encode the probable rice cpSRP43 protein from a rice yellow-green leaf mutant. A phylogenetic tree showed that an important conserved protein family, cpSRP43, is present in almost all green photosynthetic organisms such as higher plants and green algae. Sequence analysis showed that YGL9 comprises a chloroplast transit peptide, three chromodomains and four ankyrin repeats, and the chromodomains and ankyrin repeats are probably involved in protein-protein interactions. Subcellular localization showed that YGL9 is localized in the chloroplast. Expression pattern analysis indicated that YGL9 is mainly expressed in green leaf sheaths and leaves. Quantitative real-time PCR analysis showed that the expression levels of genes associated with pigment metabolism, chloroplast development and photosynthesis were distinctly affected in the ygl9 mutant. These results indicated that YGL9 is possibly involved in pigment metabolism, chloroplast development and photosynthesis in rice.

In this study, a rice spikelet mutant, multi-floret spikelet 1 (mfs1), which was derived from ethylmethane sulfonate (EMS)- treated Jinhui 10 (Oryza sativa L. ssp. indica) exhibited pleiotropic defects in spikelet development. The mfs1 spikelet displayed degenerated the empty glume, elongated the rachilla, the extra lemma-like organ and degraded the palea. Additionally, mfs1 flowers produced varied numbers of inner floral organs. The genetic analysis revealed that the mutational trait was controlled by a single recessive gene. With 401 recessive individuals from the F2 segregation population, the MFS1 gene was finally mapped on chromosome 5, an approximate 350 kb region. The present study will be useful for cloning and functional analysis of MFS1, which would facilitate understanding of the molecular mechanism involved in spikelet development in rice.