Integration of light and auxin signaling

Abstract

Light is vital for plant growth and development: It provides energy for photosynthesis, but also reliable information on seasonal timing and local habitat conditions. Light sensing is therefore of paramount importance for plants. Thus, plants have evolved sophisticated light receptors and signaling networks that detect and respond to changes in light intensity, duration, and spectral quality. Environmental light signals can drive developmental transitions such as germination and flowering, but they also continuously shape development to allow adaptation to the local habitat and microclimate. The ability to respond to a changing and sometimes unfavorable environment underlies the huge success of plants. Much of this growth and developmental plasticity is achieved by light modulation of auxin signaling systems. In this article, we examine the connections between light and auxin that elicit local responses, long distance signaling, and coordinated growth between the shoot and root.

Figure 1.

(A) From skotomorphogenesis to photomorphogenesis. From left to right, 6-day-old Arabidopsis seedlings grown under increasing amounts of white light. (B) Detecting neighbors by sensing changes in light quality. 6-day-old Arabidopsis seedlings grown under high red (R):far-red (FR) ratio light (left) or low R:FR-ratio light (right). The seedling grown in low R:FR-ratio light or vegetative shade conditions has started to elongate, part of a strategy to maximize light capture in a competitive environment.

Figure 2.

Light control of IAA production. Simplified schematics of the tryptophan-dependent auxin biosynthesis pathways (Mikkelsen et al. 2004; Lau et al. 2008; Tao et al. 2008). Some additional branches have been omitted for clarity. As phyB-Pfr enhances SUR2 and represses TTA1 transcript levels, a low R:FR-light growth condition triggers the reciprocal control, leading to an increase in IAA production.