Mechanisms that control knox gene expression in the Arabidopsis shoot

Knotted1-like homeobox (knox) genes are expressed in specific patterns with in shoot meristems and play an important role in meristem maintenance. Mise xpression of the knox genes, KNAT1 or KNAT2, in Arabidopsis produces a vari ety of phenotypes, including lobed leaves and ectopic stipules and meristem s in the sinus, the region between lobes, We sought to determine the mechan isms that control knox gene expression in the shoot by examining recessive mutants that share phenotypic characteristics with 35S::KNAT1 plants, Doubl e mutants of serrate (se),vith either asymmetric1 (as1) or asymmetric2 (as2 ) showed lobed leaves, ectopic stipules in the sinuses and defects in the t imely elongation of sepals, petals and stamens, similar to 35S::KNAT1 plant s. Ectopic stipules and in rare cases, ectopic meristems, were detected in the sinuses on plants that were mutant for pickle and either as2 or as2. KN AT1 and KNAT2 were misexpressed in the leaves and flowers of single asl and as2 mutants and in the sinuses of leaves of the different double mutants, but not in se or pickle single mutants. These results suggest that AS1 and AS2 promote leaf differentiation through repression of knox expression in l eaves, and that SE and PKL globally restrict the competence to respond to g enes that promote morphogenesis.