Mechanisms behind the puzzle: microtubule–microfilament cross-talk in pavement cell formationThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology.

Abstract

Recent studies are revealing plausible mechanisms that help explain how the two major cytoskeletal systems of plant cells interact to co-ordinate morphogenesis in diffusely expanding cells. In this article, we focus on the development of pavement cells typically found in the leaf epidermis, and highlight work that provides insights into the mechanisms that generate their complex morphology. Pavement cells interdigitate with adjacent cells, forming narrow neck regions interspersed with lobe-like projections. Earlier analysis demonstrated that distinct banding of cortical microtubules and associated accumulation of cell wall material was responsible for maintaining the neck regions during expansion. More recently, it has been determined that patches of fine actin microfilaments regulate the formation of lobing regions. This zonation into microtubule-rich bands and actin patches is coordinated by the activity of Rops, small GTPases that control a wide range of signalling pathways including ones that remodel both actin microfilament and microtubule arrays. Moreover, the formation of microtubule bands and actin patches seems to be self-reinforcing. Loss of microtubule polymers by drug treatment or mutation broadens actin patch formation, apparently by enhancing Rop interactions with a positive regulator of actin polymerization. Thus, cross-talk between microtubule and actin microfilament networks is essential for coordinating and reinforcing pavement cell morphogenesis.