Duclos Denise V, Björkman Thomas
Department of Horticultural Sciences, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456-0462, USA.
J Exp Bot. 2008;59(2):421-33. doi: 10.1093/jxb/erm327.
The regulation of reproductive development in cauliflower (Brassica oleracea var. botrytis DC) and broccoli (B. oleracea L. var. italica Plenck) is unusual in that most enlargement occurs while development is arrested at a distinct stage. Cauliflower and broccoli curds are composed of inflorescence meristems and flower buds, respectively. To determine whether this arrest is maintained by altered expression of the genes that specify these steps in Arabidopsis, the expression of each copy of their homologues (MADS-box genes BoAP1-a, BoAP1-c, BoCAL, BoFUL-a, BoFUL-b, BoFUL-c, and BoFUL-d; and non-MADS-box genes BoLFY, AP2, UFO, and BoTFL1) and the cauliflower curd-specific genes CCE1 and BoREM1 were measured simultaneously in heads that were arrested at different developmental stages by varying temperature, but had a common genotype. Transcript abundance of BoFUL paralogues and BoLFY was highest at the cauliflower stage of arrest, consistent with these genes initiating inflorescence meristems. The expression of other genes was the same regardless of the developmental stage of arrest. The expected models can therefore be excluded, wherein maintenance of arrest at the inflorescence meristem is a consequence of suppression of BoCAL, BoAP1-a, or BoLFY, or failure to suppress BoTFL1. Floral primordia and floral buds were normal in boap1-a boap1-c bocal triple mutants; therefore, other meristem identity genes can specify floral initiation (A-function) in B. oleracea. BoTFL1, a strong repressor of flowering in Arabidopsis, did not suppress the formation of the floral primordium in B. oleracea. Initiation of floral primordia and enlargement of floral buds in broccoli and cauliflower is not controlled solely by homologues of the genes that do so in Arabidopsis.
花椰菜（Brassica oleracea var. botrytis DC）和西兰花（B. oleracea L. var. italica Plenck）生殖发育的调控较为特殊，因为其大部分生长发生在发育停滞于特定阶段之时。花椰菜和西兰花的花球分别由花序分生组织和花芽组成。为了确定这种停滞是否是由拟南芥中指定这些步骤的基因表达改变所维持，在通过改变温度停滞于不同发育阶段但具有相同基因型的花球中，同时测量了它们同源基因（MADS盒基因BoAP1-a、BoAP1-c、BoCAL、BoFUL-a、BoFUL-b、BoFUL-c和BoFUL-d；以及非MADS盒基因BoLFY、AP2、UFO和BoTFL1）每个拷贝的表达，以及花椰菜花球特异性基因CCE1和BoREM1的表达。BoFUL旁系同源基因和BoLFY的转录本丰度在花椰菜停滞阶段最高，这与这些基因启动花序分生组织一致。其他基因的表达与停滞的发育阶段无关。因此，可以排除预期的模型，即在花序分生组织处的停滞维持是抑制BoCAL、BoAP1-a或BoLFY，或未能抑制BoTFL1的结果。在boap1-a boap1-c bocal三重突变体中，花原基和花芽是正常的；因此，其他分生组织特征基因可以在甘蓝中指定花的起始（A功能）。BoTFL1是拟南芥中开花的强抑制因子，但它并没有抑制甘蓝中花原基的形成。西兰花和花椰菜中花原基的起始和花芽的生长并非仅由拟南芥中相应基因的同源物控制。
