Sundås-Larsson A, Svenson M, Liao H, Engström P
Department of Physiological Botany, Uppsala University, Villavägen 6, S-752 36, Uppsala, Sweden.
Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):15118-22. doi: 10.1073/pnas.95.25.15118.
Many homeobox genes control essential developmental processes in animals and plants. In this report, we describe the first cDNA corresponding to a homeobox gene isolated from a gymnosperm, the HBK1 gene from the conifer Picea abies (L.) Karst (Norway spruce). The sequence shows distinct similarities specifically to the KNOX (knotted-like homeobox) class of homeobox genes known from different angiosperm plants. The deduced amino acid sequence of HBK1 is strikingly similar within the homeodomain (84% identical) to the maize gene Knotted1 (Kn1), which acts to regulate cell differentiation in the shoot meristem. This similarity suggested that the phylogenetic association of HBK1 with the KNOX genes might be coupled to a conservation of gene function. In support of this suggestion, we have found HBK1 to be expressed in the apical meristem in the central population of nondifferentiated stem cells, but not in organ primordia developing at the flanks of the meristem. This pattern of expression is similar to that of Kn1 in the maize meristem. We show further that HBK1, when expressed ectopically in transgenic Arabidopsis plants, causes aberrations in leaf development that are similar to the effects of ectopic expression of angiosperm KNOX genes on Arabidopsis development. Taken together, these data suggest that HBK1 has a role, similar to the KNOX genes in angiosperms, in the control of cellular differentiation in the apical meristem of spruce. The data also indicate that KNOX-gene regulation of vegetative development is an ancient feature of seed plants that was present in the last common ancestor of conifers and angiosperms.
许多同源异型盒基因控制着动植物的基本发育过程。在本报告中，我们描述了首个从裸子植物中分离出的与同源异型盒基因对应的cDNA，即来自针叶树挪威云杉（Picea abies (L.) Karst）的HBK1基因。该序列与已知的来自不同被子植物的同源异型盒基因中的KNOX（类结瘤同源异型盒）类基因表现出明显的相似性。HBK1推导的氨基酸序列在同源结构域内与玉米基因Knotted1（Kn1）惊人地相似（84%相同），Kn1在茎尖分生组织中调控细胞分化。这种相似性表明，HBK1与KNOX基因的系统发育关联可能与基因功能的保守性相关。为支持这一观点，我们发现HBK1在顶端分生组织中未分化干细胞的中央群体中表达，但在分生组织侧翼发育的器官原基中不表达。这种表达模式与玉米分生组织中Kn1的表达模式相似。我们进一步表明，当HBK1在转基因拟南芥植物中异位表达时，会导致叶片发育异常，这与被子植物KNOX基因在拟南芥发育中的异位表达效果相似。综上所述，这些数据表明HBK1在云杉顶端分生组织的细胞分化控制中具有与被子植物KNOX基因类似的作用。这些数据还表明，KNOX基因对营养发育的调控是种子植物的一个古老特征，存在于针叶树和被子植物的最后一个共同祖先中。
