Signaling in Phototropism

Abstract

Land plants cope with the same environmental challenges as animals but have the added complication of being fixed to the aground. Thus. adaptability to variable environmental circumstances is essential to plant survival and fitness. A consequence of this condition is the necessity of plants to possess sophisticated sensors to adjust to changes. Plants take the input from their myriad of physiological sensors and respond physiologically. Among these responses are the tropisms, or directional growth responses that are oriented relative to a directional stimulus. Phototropism is among one of the best-studied tropic responses where plant tissues perceive and grow directionally upon perception of a directional light stimulus - positively, or towards the light source. in the case of shoots and negatively, or away from the light source, in the case of roots. From a historical perspective, the phototropic phenomenon has been known for hundreds of years (Whippo and Hangarter in Plant Cell 18:1110-1119. 2006). Yet, only in the past few decades has the phenomenon been carefully studied to the extent that the basis of this response has become clearer. While recent analyses have yielded detailed biochemical mechanisms for some of the phototropic receptors, a great deal remains unknown. In this review of phototropism in plants, the focus is on the growth of our understanding of phototropism from the simple observations of plant growth, to the initial physiological experiments, to the most recent detailed molecular mechanisms. With the advances in genetic and molecular tools we are now in a position to understand the nature of phototropic signaling and its regulation in great detail. Over the past few years we have come to learn much about the complex interplay of molecules, including the photoreceptors, accessory proteins, transcription factors, and effector molecules necessary to perceive the light cues, modulate signaling, activate gene transcription, and elicit physiological change. While some of these players are known, undoubtedly a role for many others will emerge in future studies and such advances will provide new avenues of research.