Smith L G, Greene B, Veit B, Hake S
Department of Plant Biology, University of California, Berkeley 94720.
Development. 1992 Sep;116(1):21-30. doi: 10.1242/dev.116.1.21.
Dominant mutations of the Knotted-1 (Kn1) homeobox gene of maize alter the differentiation and growth of cells associated with leaf veins. By analyzing Kn1 transcripts and KN1 protein, we show that the gene is not expressed at high levels during the development of wild-type leaves. Instead, Kn1 is expressed in apical meristems of vegetative and floral shoots, and is downregulated as leaves and floral organs are initiated. Kn1 is also expressed in relatively undifferentiated cells within developing vascular bundles, as well as ground tissue, in immature, unelongated axes of wild-type vegetative and floral shoots. In Kn1-N2 mutant plants, quantitative, but not qualitative differences are apparent in Kn1 transcripts and KN1 protein, consistent with previous observations that dominant Kn1 mutations map to non-coding regions of the gene. Kn1 is expressed ectopically in vascular bundles within developing mutant leaves in a pattern that correlates with the phenotypic alterations produced by the Kn1-N2 mutation. Thus, Kn1 apparently alters the fates of leaf cells in which it is ectopically expressed from an early stage of leaf development. Based on these observations, we hypothesize that Kn1 functions in its wild-type context as a regulator of cell determination.
玉米的Knotted-1（Kn1）同源异型盒基因的显性突变会改变与叶脉相关的细胞的分化和生长。通过分析Kn1转录本和KN1蛋白，我们发现该基因在野生型叶片发育过程中并非高水平表达。相反，Kn1在营养枝和花茎的顶端分生组织中表达，并在叶片和花器官起始时被下调。在野生型营养枝和花茎未成熟、未伸长的轴中，Kn1也在发育中的维管束内以及基本组织中相对未分化的细胞中表达。在Kn1-N2突变体植株中，Kn1转录本和KN1蛋白存在数量上而非质量上的差异，这与之前显性Kn1突变定位于该基因非编码区的观察结果一致。Kn1在发育中的突变体叶片的维管束中异位表达，其模式与Kn1-N2突变产生的表型改变相关。因此，Kn1显然从叶片发育早期就改变了其异位表达的叶细胞的命运。基于这些观察结果，我们推测Kn1在其野生型背景下作为细胞命运决定的调节因子发挥作用。
