Introduction to special issue

What's Bugging Plants?

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Science  08 May 2009:
Vol. 324, Issue 5928, pp. 741
DOI: 10.1126/science.324_741

Plants, like other organisms, including animals, live immersed in a thriving community of microbes. The diversity of fungi, oomycetes, and bacteria with which plants interact brings both plague and benefit. The more we understand how plants tame, thwart, and succumb to their bugs, the more likely we will be able to extract new resources for antimicrobial treatments and manage agricultural challenges (Editorial, p. 691).

Microbial pathogens on the attack give the host plant several opportunities to respond. The very molecules of the microbe provide a means by which plants can identify the specific threat and take action. And the signal molecule(s) that the microbe exudes in its pathogenic actions can provide other targets. Boller and He (p. 742) discuss how innate immunity represents the first line of inducible defense against infection in both plants and animals. Takken and Tameling (p. 744) look at the biochemistry of the resistance (R) proteins as they detect microbial signals and activate plant defenses.

Phytochemicals that function primarily in warding off microbial pests warrant much more diverse analysis, as detailed by Bednarek and Osbourn (p. 746), who discuss interwoven networks of function for plant secondary metabolites. Pathogens must also get past various physical barriers at the plant surface. Some of the means by which fungi deliver their effector proteins into the plant cell are highlighted by Panstruga and Dodds (p. 748). When the various defenses fail and the pathogen gains access to the plant, both plant and pathogen make use of complex signaling networks of hormones, including jasmonate, auxin, abscisic acid, and gibberellin, as discussed by Grant and Jones (p. 750).

Microbes tend to get our most immediate attention when things go wrong in ways that affect us—when the fruit is blemished or the wheatfield destroyed. But not all microbial interactions are detrimental. Some plants benefit from interactions with their microbial community. The root nodules on soybeans, where bacteria bask in symbiotic comfort, provide the host plant with important nutrition. Oldroyd et al. (p. 753) survey our current understanding of how plants form and maintain mutually beneficial interactions with fungi and bacteria. Over time, microbial partnerships may shift between parasitism, pathogenesis, commensalism, and mutualism, as the balance of changes between partners. Burdon and Thrall (p. 755) take an organismal view of plant-microbe interactions, examining the importance of ecological factors and the need for realistic models of coevolution.

The interactions between plants and their bugs reflect an extremely complex system. This special collection of articles highlights some of the recent research progress made in understanding microbes and what they bring to the plant world.

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