Shoots and Leaves

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Science  28 Jul 2006:
Vol. 313, Issue 5786, pp. 411
DOI: 10.1126/science.313.5786.411c

Cascades of regulatory genes and signaling factors shape an indeterminate mass of cells into the complex morphologies we recognize as leaves. But why are some leaves simple and round and others complicated and curly? Hay and Tsiantis analyze how genetic networks enable one plant, Arabidopsis thaliana, to have simple undissected leaves, and a closely related plant, Cardamine hirsute, to have complex dissected leaves. Both plants express the homeobox protein KNOX, which functions as a transcription factor and affects leaf development. Both also express AS1 proteins that repress KNOX expression. The difference lies in the territory: KNOX protein confined to the shoot apical meristem results in simple leaves, whereas KNOX protein expressed in later leaf primordia results in complex leaves. The promoter sequences upstream of the KNOX coding region are critical for determining pattern of expression and hence the shape of the leaf. Although the topology of the genetic network is unchanged, in terms of which gene represses which effector, the morphological outcome is altered by changing the expression domain of the repressor. — PJH

Nat. Genet. 38, 10.1038/ng1835 (2006).

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