The cytoskeleton as a regulator and target of biotic interactions in plants

Abstract

The plant cytoskeleton is a highly dynamic and versatile intracellular scaffold composed of microtubules and actin microfilaments and plays an important role in many aspects of plant cell growth and development, including such fundamental processes as cell division, cell expansion, and intracellular organization and motility (Staiger, 2000; Wasteneys and Galway, 2003). During evolution, plants have developed mechanisms to exploit, survive, or minimize the negative impact of a diverse range of environmental factors, and in many cases the plant cytoskeleton is instrumental in mediating the plant’s response. Cytoskeletal elements, for example, translocate chloroplasts under high light conditions (Takagi, 2000), facilitate gravity sensing (Blancaflor, 2002), and direct cellular response to wounding (Foissner et al., 1996; Hush and Overall, 1996). In addition to these abiotic factors, plants also encounter and must deal with a range of other organisms that may be potential partners or pathogens. Once again, the plant cytoskeleton plays a key role. In many ways, biotic factors in the environment present a greater challenge to the plant than do abiotic stresses because living organisms, like their plant hosts, are continually evolving. Potential pathogens develop new ways of avoiding or overcoming existing plant defenses; symbionts may attain aggressive traits or lose beneficial ones. Plants must thus constantly refine existing defenses and develop new strategies to maintain an upper hand in their interactions with other organisms. Changes in the organization of the plant cytoskeleton during plant interactions with microbial and other organisms are complex and varied, and much still remains to be elucidated, especially in terms of the molecules that signal and bring about the dramatic reorganizations that are often observed. This diversity and complexity is, no doubt, a product of many factors, including differences in signal exchanges between the interacting partners and the relative dominance of one or other organism. In many cases, the changes that are observed are likely to be the net result of instructions from both interacting organisms. In this article, we review current understanding of the role of the plant cytoskeleton in defense against invading fungal and oomycete pathogens and in establishing symbiotic relationships with mycorrhizal fungi and bacteria. We also review current information on the targeting of the plant cytoskeleton by viruses to enhance their movement and by signals from the female plant tissues as part of a mechanism of self-incompatibility. Show more