Reduced leaf complexity in tomato wiry mutants suggests a role for PHAN and KNOX genes in generating compound leaves.
2003
Recent work on species with simple leaves suggests that the juxtaposition
of abaxial (lower) and adaxial (upper) cell fates (dorsiventrality) in leaf
primordia is necessary for lamina outgrowth. However, how leaf dorsiventral
symmetry affects leaflet formation in species with compound leaves is largely
unknown. In four non-allelic dorsiventrality-defective mutants in tomato,
wiry, wiry3, wiry4 and wiry6 , partial or complete loss of
ab-adaxiality was observed in leaves as well as in lateral organs in the
flower, and the number of leaflets in leaves was reduced significantly.
Morphological analyses and expression patterns of molecular markers for
ab-adaxiality [ LePHANTASTICA ( LePHAN ) and LeYABBY B
( LeYAB B )] indicated that ab-adaxial cell fates were altered in
mutant leaves. Reduction in expression of both LeT6 (a tomato
KNOX gene) and LePHAN during post-primordial leaf
development was correlated with a reduction in leaflet formation in the wiry
mutants. LePHAN expression in LeT6 overexpression mutants
suggests that LeT6 is a negative regulator of LePHAN. KNOX
expression is known to be correlated with leaflet formation and we show that
LeT6 requires LePHAN activity to form leaflets. These
phenotypes and gene expression patterns suggest that the abaxial and adaxial
domains of leaf primordia are important for leaflet primordia formation, and
thus also important for compound leaf development. Furthermore, the regulatory
relationship between LePHAN and KNOX genes is different from
that proposed for simple-leafed species. We propose that this change in the
regulatory relationship between KNOX genes and LePHAN plays
a role in compound leaf development and is an important feature that
distinguishes simple leaves from compound leaves.
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