The maize gene liguleless2 encodes a basic leucine zipper protein involved in the establishment of the leaf blade-sheath boundary.
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.
Walsh
J
J
Department of Plant and Microbial Biology, University of California, Berkley, 94720, USA.
Waters
C A
CA
Freeling
M
M
D000595:Amino Acid Sequence; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D016350:Leucine Zippers / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics* / Q000648:ultrastructure*
D050976:Basic-Leucine Zipper Transcription Factors; C105241:LG1 protein, Zea mays; C110592:LIGULELESS2 protein, Zea mays; D010940:Plant Proteins; D012333:RNA, Messenger