被子植物的花由花分生组织(又称花原基)形成。花分生组织产生于花序分生组织。与花序分生组织相比，花分生组织有限生长并且产生特定大小和形状的花器官，这个过程伴随花器官的形成和干细胞活性的终止。在拟南芥中，MADS家族转录因子 APETALA1 (AP1) 调控花发育过程的起始，并且作为花同源异形基因调控外层两轮花器官的形成。此外，AP1可以抑制最外轮花器官萼片叶腋处形成更多花原基。尽管对于AP1调控开花和外轮花器官形成的机制已经被广泛研究，但是 AP1 到底如何抑制萼片叶腋处的干细胞活性依然是个悬而未决的问题。
焦雨铃课题组的研究表明 AP1 可以通过直接抑制细胞分裂素合成基因 LONELY GUY 1 (LOG1) 及直接激活细胞分裂素降解酶 CYTOKININ OXIDASE3 (CKX3) 以减少 AP1 基因表达区域的细胞分裂素含量，从而维持了正常的花分生组织的有限生长。此研究结果对于分子育种，特别是作物穗粒数的控制，有一定借鉴意义。
该研究成果于2014年4月21日在线发表于PNAS 杂志。焦雨铃课题组的博士研究生韩莹莹为该文章的第一作者。该研究得到了科技部、自然科学基金委和中科院的资助。细胞分裂素的测定由国家植物基因中心(北京)植物激素平台褚金芳博士等协助完成。
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. |
