75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

195 ARROW1 (ARO1), a Novel Regulator of Leaf Polarity in Arabidopsis
Tengbo Huang, Jeon Hong, Randall Kerstetter
Waksman Institute, Rutgers University
Normal leaf morphogenesis requires the proper specification of adaxial-abaxial polarity. Several classes of genes
have been demonstrated to control the specification of abaxial and adaxial fate in lateral organs. Among these, KANADI
(KAN) genes are essential promoters of abaxial identity. Here, we describe an enhancer of kan that shows significant
loss of leaf polarity when combined with kan1 kan2 mutants. This gene we have dubbed ARROW1 (ARO1) because
aro1 mutant has arrowhead-shaped leaves. ARO1 encodes a putative sequence-specific RNA-binding protein of the
Pumilio/PUF domain family several of which have been shown to function as inhibitors of translation in animals. aro1
plants display pleiotropic developmental defects indicating roles in leaf, root, and flower development. It also interacts
with other developmental mutants involved in leaf polarity, such as ASYMMETRIC LEAVES1 (AS1), ASYMMETRIC
LEAVES2 (AS2) and REVOLUTA (REV). These features indicate that ARO1 represents a novel regulator of diverse
pathways during plant development.
196 The Arabidopsis homeodomain proteins SAW1 and SAW2 control leaf development
through negative regulation of KNOX function
Ravi Kumar, Kumuda Kushalappa, Dietmute Godt, Mark Pidkowich, Sandro Pastorelli, Shelley Hepworth, George
Haughn
University of British Columbia, Vancouver, BC, Canada
In Arabidopsis, the BEL1–like TALE homeodomain gene family consists of 13 members that form heterodimeric
complexes with the Class 1 KNOX TALE homeodomain proteins including STM and BP. The BEL1-like protein
BELLRINGER (BLR) functions together with STM and BP in the shoot apex to control meristem identity/function and
promote correct shoot architecture. We have characterized two additional BEL1-like genes, SAWTOOTH1 (SAW1) and
SAWTOOTH2 (SAW2) that, in contrast to BLR, are expressed in lateral organs but not in meristems. Saw1 and saw2
single mutants have no obvious phenotype but the saw1 saw2 double mutant has increased leaf serrations indicating
that SAW1 and SAW2 act redundantly to limit leaf margin growth. Consistent with this hypothesis, over-expression of
SAW1 suppresses overall growth of the plant shoot. BP is ectopically expressed in the leaf serrations of saw1 saw2 double
mutants. Ectopic expression in leaves of Class 1 KNOX genes has been observed previously in loss-of-function mutants
of AS1, a gene encoding a MYB transcription factor. For this reason we explored the relationship between SAW1 and
BP in an as1 mutant. Over-expression of SAW1 in an as1 mutant suppresses the as1 leaf phenotype and reduces ectopic
BP leaf expression suggesting that SAW1 may act downstream of AS1. However, the domain of ectopic expression of
BP in as1 leaves and the morphology of as1 leaves are distinct from those observed for the saw1 saw2 double mutant.
In addition, SAW1 transcript levels remain unchanged in the leaves of as1 mutant. Taken together, our data suggest that
SAW1/SAW2 acts independently of AS1 to establish leaf shape by repressing growth in specific subdomains of the leaf
margin at least in part by repressing expression of one or more of the KNOX genes.