As life's diversity demonstrates, nature has a pretty large toolbox for designing adaptations. While in many ways an efficient builder, it often reuses blueprints, even if not starting with the same tools. Analogous wing structures in bird and bat suggest a why-mess-with-success ethos. New World cacti and desert-dwelling Euphorbiaceae in the Old World share protective spines and photosynthesizing stems even though the last common ancestor predates such modifications.
Beyond structural adaptations, researchers are investigating convergent evolution at the molecular level, and this may allow for broader comparisons even between plants and animals. Both, of course, share the building blocks and fundamental biochemistry that evolved before the two kingdoms presumably diverged from common single-celled ancestors. But with their radically different cell structures, plants and animals were thought to have pursued largely independent evolutionary routes. Such disparity was reflected in the lack of interaction between the respective research communities.
But much is changing, especially with respect to the study of innate immunity, which turns out to involve strikingly similar mechanisms in both plants and animals. One can find resemblances in the receptors that recognize pathogenic components such as lipopolysaccharide; in the signaling systems that initiate responses through kinase cascades; and in the defense mechanisms, including reactive molecules such as nitric oxide, says Jonathan Jones, senior scientist at the Sainsbury Laboratory of the John Innes Centre in Norwich, UK.
Moreover, says Jones, autoimmune disorders can develop in plants as well as animals. In many cases, researchers consider plant and animal innate-immunity analogs to have evolved independently, because the underlying genes involved are radically different. Here, convergence is occurring purely at the functional level, according to Daniel Klessig, president and CEO of Boyce Thompson Institute (BTI) for Plant Research in Ithaca, NY. But now, say some, both functional and genetic similarities between plant and animal immunity are leading to crosspollination between the respective research fields.
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Functional similarities can exist without accompanying sequence homologies. Klessig offers parallels in nitric oxide production between plants and animals. Nitric oxide is believed to exert direct antimicrobial effects by interfering with protein function and forming cytotoxic oxidants.
Klessig's group recently discovered the enzyme responsible for nitric oxide production in plants, a variant of the glycine decarboxylase...