Fowler J E, Freeling M
Department of Plant Biology, University of California, Berkeley 94720, USA.
Dev Genet. 1996;18(3):198-222. doi: 10.1002/(SICI)1520-6408(1996)18:3<198::AID-DVG2>3.0.CO;2-4.
The three major components of the maize leaf are the blade, the sheath, and at their junction, ligular region. Each exhibits specific cell types and organization. Four dominant Liguleless (Lg) mutations (Lg3-O, Lg4-O, Lg347, and Lg9167) in at least three different genes cause a similar morphological phenotype in leaves, although each mutation affects a distinct domain of the blade. Mutant leaves display regions of altered cell fate in the blade, accompanied by elimination of ligule and auricle at their wild-type positions and development of ligule and auricle in the blade at the borders of the altered regions. The affected blade cells are transformed into sheath-like cells, as determined by morphological and genetic tests. Lg4-O expressivity is highly dependent on genetic background. For example, two different backgrounds nay specify converse patterns of phenotypic expression. Lg4-O expressivity is also affected by the heterochronic mutation Teopod2 (Tp2). Gene dosage experiments indicates Lg4-O is a neomorph. Interactions between recessive lg mutations (which eliminate ligular structures) and the dominant Lg mutations suggest that the lg+ genes act after the Lg mutations. Lg3-O and Lg4-O act semidominantly, and interact with each other and with other mutations in the Knotted1 (Kn1)-like family (a family in which dominant mutant alleles cause blade to sheath transformation phenotypes). These interactions suggest that the above Kn1-like mutations may function similarly in the leaf. We discuss the similarities between the Lg mutations and the other mutations of the Kn1-like family, which led us to postulate that Ig3 and Ig4 are members of a growing family of kn1-like (knox) homeobox genes that are identified by dominant mutant alleles causing leaf transformation phenotypes. We also propose that certain key characteristics of this family of dominant neomorphic mutations are important for generating meaningful morphological changes during evolution.
玉米叶片的三个主要组成部分是叶片、叶鞘以及它们的连接处——叶舌区域。每个部分都呈现出特定的细胞类型和组织结构。至少三个不同基因中的四个显性无叶舌（Lg）突变（Lg3 - O、Lg4 - O、Lg347和Lg9167）在叶片中会导致相似的形态表型，尽管每个突变影响叶片的不同区域。突变叶片在叶片中表现出细胞命运改变的区域，同时在其野生型位置的叶舌和叶耳消失，而在改变区域的边界处叶片中出现叶舌和叶耳。通过形态学和遗传学测试确定，受影响的叶片细胞转变为叶鞘样细胞。Lg4 - O的表达高度依赖于遗传背景。例如，两种不同的背景可能会指定相反的表型表达模式。Lg4 - O的表达也受到异时突变Teopod2（Tp2）的影响。基因剂量实验表明Lg4 - O是一个新等位基因。隐性lg突变（消除叶舌结构）与显性Lg突变之间的相互作用表明，lg +基因在Lg突变之后起作用。Lg3 - O和Lg4 - O呈半显性作用，并且它们之间以及与类结瘤1（Kn1）家族中的其他突变相互作用（在该家族中，显性突变等位基因会导致叶片向叶鞘转变的表型）。这些相互作用表明，上述类Kn1突变在叶片中可能具有相似的功能。我们讨论了Lg突变与类Kn1家族的其他突变之间的相似性，这使我们推测Ig3和Ig4是一个不断扩大的类kn1（knox）同源异型框基因家族的成员，这些基因通过导致叶片转变表型的显性突变等位基因得以鉴定。我们还提出，这个显性新等位基因突变家族的某些关键特征对于在进化过程中产生有意义的形态变化很重要。
