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近日，中國科學院上海植物生理生態研究所薛紅衛與湖南農業大學肖浪濤團隊在Plant Physiology在線發表了題為「Dynamic cytology and transcriptional regulation of rice lamina joint development」 的研究論文。該研究通過系統的形態學和細胞學觀察以及高通量基因表達譜分析，揭示了葉枕發育的細胞學基礎和分子調控機制，為水稻葉傾角調控研究和株型改良提供了重要線索。
Fig8. A schematic model of rice lamina joint development.
水稻葉枕是葉片基部與葉鞘連接的帶狀部分，其發育過程中形成的葉鞘、葉片之間的夾角即為葉傾角，是構成水稻株型的重要因素之一。研究表明，適當的葉傾角有利於提高水稻光合效率，通過合理密植，能夠有效提高產量。目前對水稻葉枕發育/葉傾角調控的研究多集中在對葉傾角變化的表型描述上，對其形成的細胞學基礎和分子調控機理及互作調控網絡的解析仍顯不足。本研究對水稻葉枕發育過程進行了系統的形態學和細胞學觀察，發現不同葉片葉傾角的增大呈現出相似的「S」形變化；切片分析表明葉枕發育中近、遠軸面的薄壁細胞和厚壁細胞的大小和數目發生了劇烈變化，葉傾角增大主要是由兩側細胞的不對稱分裂和延伸造成的。進一步利用全基因組表達譜晶片對葉枕發育涉及的生物學過程、基因表達變化和調控網絡進行的系統研究表明，與葉枕發育中的細胞學變化相一致，細胞分裂與生長、激素合成與信號、轉錄因子、蛋白激酶等相關編碼基因在葉枕不同發育時期具有特定的表達模式。
植物激素是葉傾角形成的重要調節因子，通過測定葉枕不同發育階段中的多種激素含量並結合一個生長素含量改變的水稻突變體（lc1-D）的基因表達譜，分析表明油菜素甾醇、生長素、赤黴素、細胞分裂素等在葉枕發育的早期促進細胞分化和生長；乙烯、茉莉酸、水楊酸等主要在後期調節葉枕的成熟、衰老和逆境響應；不同激素見通過互作調控了葉枕發育。這些結果初步闡明了葉枕發育的細胞學基礎和形成機制，建立了葉枕發育的調控網絡，對後續研究和株系改良具有重要指導意義。
該研究由上海植生所和湖南農業大學合作完成，博士生周莉娟為論文第一作者。相關工作得到了國家自然科學基金委、國家科技部的資助。
Rice leaf angle is determined by lamina joint and an important agricultural trait determining leaf erectness and hence the photosynthesis efficiency and grain yield. Genetic studies reveal a complex regulatory network of lamina joint development; however, the morphological changes, cytological transitions, and underlying transcriptional programming remain to be elucidated. A systemic morphological and cytological study reveals a dynamic developmental process and suggests a common but distinct regulation of lamina joint. Successive and sequential cell division and expansion, cell wall thickening and programmed cell death at the adaxial or abaxial sides conduct the cytological basis of lamina joint, and the increased leaf angle results from the asymmetric cell proliferation and elongation. Analysis of the gene expression profiles at four distinct developmental stages ranging from initiation to senescence showed that genes related to cell division and growth, hormone synthesis and signaling, transcription (transcription factors) and protein phosphorylation (protein kinases) exhibit distinct spatial-temporal patterns, during lamina joint development. Phytohormones play crucial roles by promoting cell differentiation and growth at early stages or regulating the maturation and senescence at later stages, which is consistent with the quantitative analysis of hormones at different stages. Further comparison with the gene expression profile of leaf inclination1 (lc1-D), a mutant with decreased auxin and increased leaf angle, indicates the synergistic effects of hormones in regulating lamina joint. These results reveal a dynamic cytology of rice lamina joint that is fine-regulated by multiple factors, providing informative clues for illustrating the regulatory mechanisms of leaf angle and plant architecture.
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