被子植物的花由花分生組織(又稱花原基)形成。花分生組織產生于花序分生組織。與花序分生組織相比，花分生組織有限生長并且產生特定大小和形狀的花器官，這個過程伴隨花器官的形成和干細胞活性的終止。在擬南芥中，MADS家族轉錄因子 APETALA1 (AP1) 調控花發育過程的起始，并且作為花同源異形基因調控外層兩輪花器官的形成。此外，AP1可以抑制最外輪花器官萼片葉腋處形成更多花原基。盡管對于AP1調控開花和外輪花器官形成的機制已經被廣泛研究，但是 AP1 到底如何抑制萼片葉腋處的干細胞活性依然是個懸而未決的問題。
焦雨鈴課題組的研究表明 AP1 可以通過直接抑制細胞分裂素合成基因 LONELY GUY 1 (LOG1) 及直接激活細胞分裂素降解酶 CYTOKININ OXIDASE3 (CKX3) 以減少 AP1 基因表達區域的細胞分裂素含量，從而維持了正常的花分生組織的有限生長。此研究結果對于分子育種，特別是作物穗粒數的控制，有一定借鑒意義。
該研究成果于2014年4月21日在線發表于PNAS 雜志。焦雨鈴課題組的博士研究生韓瑩瑩為該文章的第一作者。該研究得到了科技部、自然科學基金委和中科院的資助。細胞分裂素的測定由國家植物基因中心(北京)植物激素平臺褚金芳博士等協助完成。
原文摘要：
Cytokinin pathway mediates APETALA1 function in the establishment of determinate floral meristems in Arabidopsis
Yingying Han, Cui Zhang, Haibian Yang and Yuling Jiao
In angiosperms, after the floral transition, the inflorescence meristem produces floral meristems (FMs). Determinate growth of FMs produces flowers of a particular size and form. This determinate growth requires specification of floral organs and termination of stem-cell divisions. Establishment of the FM and specification of outer whorl organs (sepals and petals) requires the floral homeotic gene APETALA1 (AP1). To determine FM identity, AP1 also prevents the formation of flowers in the axils of sepals. The mechanisms underlyingAP1 function in the floral transition and in floral organ patterning have been studied extensively, but howAP1 terminates sepal axil stem-cell activities to suppress axillary secondary flower formation remains unclear. Here we show that AP1 regulates cytokinin levels by directly suppressing the cytokinin biosynthetic gene LONELY GUY1 and activating the cytokinin degradation gene CYTOKININ OXIDASE/DEHYDROGENASE3. Restoring the expression of these genes to wild-type levels in AP1-expressing cells or suppressing cytokinin signaling inhibits indeterminate inflorescence meristem activity caused by ap1 mutation. We conclude that suppression of cytokinin biosynthesis and activation of cytokinin degradation mediates AP1 function in establishing determinate FM. A deeper understanding of axil-lateral meristem activity provides crucial information for enhancing yield by engineering crops that produce more elaborated racemes. |
