THE ASYMMETRIC LEAVES2 (AS2) GENE OF ARABIDOPSIS THALIANA REGULATES LAMINA FORMATION AND IS REQUIRED FOR PATTERNING OF LEAF VENATION

摘要

To understand the molecular mechanisms behind symmetrical development of leaf, we have analyzed the asymmetric leaves2 (as2) mutant of A. thaliana, which generated leaf lobes and leaflet-like structures from the petioles of leaves in a bilaterally asymmetric manner. The delayed formation of the primary vein and the asymmetric formation of secondary veins were apparent in leaf primordia of as2 plants. A distinct midvein, which is the thickest vein and is located in the longitudinal center of the leaf lamina of wild-type plants, was often rudimentary even in mature as2 leaves. However, several parallel veins of very similar thickness were evident in such leaves. The malformed veins were visible prior to the development of asymmetry of the leaf lamina, and were maintained in the mature as2 leaves. Culture in vitro on phytohormone-free medium of leaf sections from the as2 mutants and from the asymmetric leaves] (as1) mutant, which has a phenotype similar to that of as2, revealed an elevated potential in both cases for regeneration of shoots from leaf cells. Analysis by the reverse transcription-polymerase chain reaction showed that AS2 and AS! negatively regulates the homeobox genes KNAT1, KNAT2 and KNAT6 in leaves. Taken together, our results suggest that AS2 and AS1 are involved in establishment of leaf venation and the formation of symmetric leaf lamina, which might be related to repression of expression of the homeobox genes in leaves.