title: Bundle sheath suberization in grass leaves: multiple barriers to characterization.
abstract: High-yielding, stress-tolerant grass crops are essential to meet future food and energy demands. Efforts are underway to engineer improved varieties of the C3 cereal crop rice by introducing NADP-malic enzyme C4 photosynthesis using maize as a model system. However, several modifications to the rice leaf vasculature are potentially necessary, including the introduction of suberin lamellae into the bundle sheath cell walls. Suberized cell walls are ubiquitous in the root endodermis of all grasses, and developmental similarities are apparent between endodermis and bundle sheath cell walls. Nonetheless, there is considerable heterogeneity in sheath cell development and suberin composition both within and between grass taxa. The effect of this variation on physiological function remains ambiguous over forty years after suberin lamellae were initially proposed to regulate solute and photoassimilate fluxes and C4 gas exchange. Interspecies variation has confounded efforts to ascribe physiological differences specifically to the presence or absence of suberin lamellae. Thus, specific perturbation of suberization within a uniform genetic background is needed, but, until recently, the genetic resources to manipulate suberin composition in the grasses were largely unavailable. The recent dissection of the suberin biosynthesis pathway in model dicots and the identification of several promising candidate genes in model grasses will facilitate the characterization of the first suberin biosynthesis genes in a monocot. Much remains to be learned about the role of bundle sheath suberization in leaf physiology, but the stage is set for significant advances in the near future.
authors.affiliation: Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA Donald Danforth Plant Science Center, St Louis, MO 63132, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Mertz
authors.affiliation: Donald Danforth Plant Science Center, St Louis, MO 63132, USA tbrutnell@danforthcenter.org.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Brutnell
mesh_terms: D053898:Biosynthetic Pathways; D002473:Cell Wall / Q000648:ultrastructure*; D018556:Crops, Agricultural; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D008055:Lipids / Q000096:biosynthesis*; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D058526:Plant Vascular Bundle / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D006109:Poaceae / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D008055:Lipids; C065875:suberin
keywords: Bundle sheath; C4; cell wall; endodermis; grasses; mestome sheath; physiology; suberin.