Minsung Kim | PubMed Health

PubMed2003

The expression domain of PHANTASTICA determines leaflet placement in compound leaves.

Diverse leaf forms in nature can be categorized as simple or compound. Simple leaves, such as those of petunia, have a single unit of blade, whereas compound leaves, such as those of tomato, have several units of blades called leaflets. Compound leaves can be pinnate, with leaflets arranged in succession on a rachis, or palmate, with leaflets clustered together at the leaf tip. The mechanisms that generate these various leaf forms are largely unknown. The upper (adaxial) surface is usually different from the bottom (abaxial) surface in both simple and compound leaves. In species with simple leaves, the specification of adaxial and abaxial cells is important for formation of the leaf blade, and the MYB transcription factor gene PHANTASTICA (PHAN) is involved in maintaining the leaf adaxial (upper) domain. Here we show that downregulation of PHAN is sufficient to reduce the adaxial domain of leaf primordia and to change pinnate compound leaves into palmate compound leaves. Furthermore, this mechanism seems to be shared among compound leaves that arose independently.

Down-Regulation↗

PubMed2003

Regulating shapes and sizes.

Mutations at many loci lead to altered shapes and sizes, suggesting complex regulation of the overall morphology of an organism. Two recent studies present data on how orientation of growth axes and perception of maturation signals might regulate growth processes.

Animals↗

PubMed2003

Reduced leaf complexity in tomato wiry mutants suggests a role for PHAN and KNOX genes in generating compound leaves.

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.

Gene Expression Regulation, Plant↗