Minisymposium 23: Cytoskeleton

Abs # 37004: MUSTACHES is required for guard cell morphogenesis in Arabidopsis

Presenter:	Nadeau, Jeanette A, nadeau.5@osu.edu
Authors	Nadeau, Jeanette A (A)   Nakagawa, Tsuyoshi  (B)   Lucas, Jessica  (A)   Zhao, Liming  (A)   Heine, George  (A)   Sack, Fred D (A)
Affiliations:	(A): Department of Plant Biology, The Ohio State University (B): Research Institute of Molecular Genetics, Shimane University

Stomata consist of two guard cells surrounding a pore and are necessary for gas exchange through the shoot epidermis. During differentiation guard cells acquire a unique shape and specialized cell wall architecture that allows them to function together as a turgor-operated valve. Despite the importance of this process, the molecular genetic and cell biological processes involved in stomatal differentiation are largely unknown. Here we describe a locus, MUSTACHES (MUS), that is required for guard cell shape and pore formation. Guard cells arise from the symmetrical division of a progenitor cell followed by deposition of a lens-shaped cell wall thickening between the two cells. This area later separates to form the pore. In addition, developing guard cells expand in a regulated fashion to attain the kidney shape necessary for stomatal valve action. During differentiation, guard cells develop a radial array of cortical microtubules focused at the developing pore site. This array is believed to guide the radial deposition of cellulose microfibrils that restricts turgor-driven expansion. In mustaches, many guard cells are abnormal shapes and lack symmetry between the pair. These cells also exhibit spatial defects in the localized deposition of new cell wall material. Pore opening is impeded in strongly affected guard cell pairs, yet overall plant morphology is unaffected. Radial microtubule arrays are either absent or skewed in abnormal mus guard cells, but shape disruptions are not associated with altered cell identity because abnormal cells express guard cell-specific molecular markers. Collectively these observations suggest that MUS plays a role in organized wall building, through targeted vesicular deposition and/or controlled deposition of cellulose microfibrils. Furthermore, the loss of symmetry between guard cell pairs in mus implies that it participates in morphogenetic events coordinated between the cell pair. MUS encodes an LRR-containing receptor kinase belonging to a family with no previously known function. Furthermore, MUS is expressed in a pattern consistent with its potential role in signaling during the latter stages of the stomatal pathway. These observations suggest that extracellular signals may be linked through MUS to the spatial organization of the cytoskeleton necessary to control guard cell morphogenesis.