Steynen Quintin J, Schultz Elizabeth A
Department of Biological Sciences, University of Lethbridge, Lethbridge, AB, TIK 3M4, Canada.
Development. 2003 Oct;130(19):4695-708. doi: 10.1242/dev.00689.
As in most dicotyledonous plants, the leaves and cotyledons of Arabidopsis have a closed, reticulate venation pattern. This pattern is proposed to be generated through canalization of the hormone auxin. We have identified two genes, FORKED 1 (FKD1) and FORKED 2 (FKD2), that are necessary for the closed venation pattern: mutations in either gene result in an open venation pattern that lacks distal meeting. In fkd1 leaves and cotyledons, the defect is first evident in the provascular tissue, such that the distal end of the newly forming vein does not connect to the previously formed, more distal vein. Plants doubly mutant for both genes have widespread defects in leaf venation, suggesting that the genes function in an overlapping manner at the distal junctions, but act redundantly throughout leaf veins. Expression of an auxin responsive reporter gene is reduced in fkd1 leaves, suggesting that FKD1 is necessary for the auxin response that directs vascular tissue development. The reduction in reporter gene expression and the fkd1 phenotype are relieved in the presence of auxin transport inhibition. The restoration of vein junctions in situations where auxin concentrations are increased indicates that distal vein junctions are sites of low auxin concentration and are particularly sensitive to reduced FKD1 and FKD2 activity.
与大多数双子叶植物一样，拟南芥的叶片和子叶具有封闭的网状叶脉模式。这种模式被认为是通过生长素的管道化作用产生的。我们鉴定出了两个基因，即叉状 1（FKD1）和叉状 2（FKD2），它们对于封闭叶脉模式是必需的：任一基因发生突变都会导致缺乏远端交汇的开放叶脉模式。在fkd1的叶片和子叶中，缺陷首先在原维管组织中显现，使得新形成叶脉的远端无法与先前形成的、更靠远端的叶脉相连。这两个基因的双突变体植株在叶脉方面存在广泛缺陷，这表明这些基因在远端连接处以重叠方式发挥作用，但在整个叶脉中发挥冗余作用。生长素响应报告基因在fkd1叶片中的表达降低，这表明FKD1对于指导维管组织发育的生长素响应是必需的。在存在生长素运输抑制的情况下，报告基因表达的降低和fkd1的表型得到缓解。在生长素浓度增加的情况下叶脉连接的恢复表明，远端叶脉连接是生长素浓度较低的部位，并且对FKD1和FKD2活性降低特别敏感。
