On growth and formins.

Development of the plant aerial organs epidermis involves a complex interplay of cytoskeletal rearrangements, membrane trafficking-dependent cell surface expansion, and intra- and intercellular signaling, resulting in a pattern of perfectly interlocking pavement cells. While recent detailed in vivo observations convincingly identify microtubules rather than actin as key players at the early stages of development of pavement cell lobes in Arabidopsis, mutations affecting the actin-nucleating ARP2/3 complex are long known to reduce pavement cell lobing, suggesting a central role for actin. We have now shown that functional impairment of the Arabidopsis formin FH1 enhances both microtubule dynamics and pavement cell lobing. While formins are best known for their ability to nucleate actin, many members of this old gene family now emerge as direct or indirect regulators of the microtubule cytoskeleton, and our findings suggest that they might co-ordinate action of the two cytoskeletal systems during pavement cell morphogenesis.