Walsh J, Waters C A, Freeling M
Department of Plant and Microbial Biology, University of California, Berkley, 94720, USA.
Genes Dev. 1998 Jan 15;12(2):208-18. doi: 10.1101/gad.12.2.208.
The blade and sheath of a maize leaf are separated by a linear epidermal fringe, the ligule, and two wedge-like structures, the auricles. In plants homozygous for the null mutation, liguleless2-reference (lg2-R), the ligule and auricles are often absent or positioned incorrectly and the blade-sheath boundary is diffuse. This phenotype is in contrast to that of liguleless1-reference (lgl-R) mutant plants, which have a more defined boundary even in the absence of the ligule and auricles. Additionally, mosaic analysis indicates the lg2-R phenotype is cell-nonautonomous and the lg1-R phenotype is cell-autonomous. Using scanning electron microscopy we show that lg2-R mutant plants are affected before the first visible sign of ligule and auricle formation. We have cloned the Lg2+ gene through a Mutator-8 transposon insertion allele, and verified it with five independently derived alleles. The comparison of genomic DNA and cDNA sequences reveals an open reading frame encoding a protein of 531 amino acids with partial homology to a subclass of plant basic leucine zipper (bZIP) transcription factors. Although a large body of molecular and biochemical characterization exists on this subclass of bZIP proteins, our work represents the first report of a mutant phenotype within this group. A specific reverse transcriptase (RT)-PCR assay shows LG2 mRNA expression in meristem/developing ligule regions. RT-PCR also shows that LG2 mRNA accumulation precedes that of LG1 mRNA. The mutant phenotype and expression analysis of lg2 suggest an early role in initiating an exact blade-sheath boundary within the young leaf primordia.
玉米叶片的叶片和叶鞘由一条线状表皮边缘（叶舌）和两个楔形结构（叶耳）分隔开。在无叶舌2参考系（lg2-R）纯合突变体植株中，叶舌和叶耳常常缺失或位置不正确，叶片与叶鞘的边界模糊不清。这种表型与无叶舌1参考系（lgl-R）突变体植株相反，后者即使在没有叶舌和叶耳的情况下，边界也更清晰。此外，镶嵌分析表明，lg2-R的表型是非细胞自主性的，而lg1-R的表型是细胞自主性的。通过扫描电子显微镜，我们发现lg2-R突变体植株在叶舌和叶耳形成的首个可见迹象出现之前就受到了影响。我们通过一个Mutator-8转座子插入等位基因克隆了Lg2+基因，并用五个独立衍生的等位基因进行了验证。基因组DNA和cDNA序列的比较揭示了一个开放阅读框，其编码一个含有531个氨基酸的蛋白质，该蛋白质与植物碱性亮氨酸拉链（bZIP）转录因子的一个亚类有部分同源性。尽管关于这个bZIP蛋白亚类已经有大量的分子和生化特征描述，但我们的研究是该组内突变体表型的首次报道。一种特异性逆转录酶（RT）-PCR分析显示LG2 mRNA在分生组织/发育中的叶舌区域表达。RT-PCR还表明LG2 mRNA的积累先于LG1 mRNA。lg2的突变体表型和表达分析表明，它在幼叶原基内启动精确的叶片-叶鞘边界方面起早期作用。
