Genetic relationship between angustifolia3 and extra-small sisters highlights novel mechanisms controlling leaf size.

Coordination between cell proliferation and cell expansion is pivotal in leaf size determination. A group of mutants that are impaired in cell proliferation such as the angustifolia3 (an3) has provided a clue to understanding how these cellular processes are coordinated. In these mutants, impaired cell proliferation is accompanied by enhanced cell enlargement. We propose to call this phenomenon "compensated cell enlargement." Previously, we isolated ten extra-small sisters (xs) mutants that are specifically impaired in post-mitotic cell expansion and found that several xs mutations are able to suppress compensated cell enlargement in an3. Thus, the enhanced cell expansion observed in an3 results from the hyperactivation of post-mitotic cell expansion involving specific members of the XS gene family. These results suggested that cell proliferation process(es) and post-mitotic cell expansion process(es) are somehow linked in an as yet unknown fashion in leaf primordia. In this addendum, we propose possible models for the linking mechanisms that coordinate AN3-dependent cell proliferation and XS-dependent cell expansion in leaf development.