Cryptochrome-mediated light responses in plants

Abstract

Cryptochromes (CRYs) are photolyase-like flavoproteins that have been found in all evolutionary lineages. Plant and animal CRYs are no longer DNA-repairing enzymes but they apparently gained other biochemical functions in evolution. Plant CRYs are UV-A/blue-light photoreceptors and play a pivotal role in plant growth and development, whereas animal CRYs act as either photoreceptors or transcription regulators. The first CRY gene was isolated from Arabidopsis thaliana, which regulates stem growth, flowering time, stomatal opening, circadian clock, and other light responses. CRYs are also found in all major crops investigated, with additional functions discovered, such as seed germination, leaf senescence, and stress responses. In this chapter, we will review some aspects of CRY-mediated light responses in plants. Readers are referred to other review articles for photochemistry and signal transduction mechanism of plant CRYs (Liu et al., 2010, 2011; Fankhauser and Ulm, 2011) [1-3].

Keywords: Blue-light responses; Cryptochrome; Photoreceptors.

Figure 1.. Cryptochrome-mediated light inhibition of hypocotyl elongation

The Arabidopsis seedlings of WT (Col) and cry1cry2 double mutant grown in dark or continuous blue, red, or far-red light conditions, showing blue light-specific long hypocotyl phenotype of the cry1cry2 double mutant.

Figure 2.. Cryptochrome-mediated photoperiodic regulation of floral initiation

WT (Col) and cry1cry2 double mutants grown under long-day (LD) or short-day (SD) conditions, showing the late-flowering phenotype of cry1cry2 double mutants under LD.

Figure 3.. Cryptochrome-mediated stomatal opening and development in response to lights. (Images are taken from published articles in PNAS. 102: 12270-12275 and Plant Cell. 21: 2624-2641 with the authors’ permission)

A. Stomata opening of the WT, cryl, cry2, cry1cry2, CRY1-ox, and CRY2-ox plants after illuminated with blue light, showing the enhanced light response of stomata opening in CRY1-ox plants. (Mao, J. et al., PNAS. 102: 12270-12275) B.The abaxial cotyledon epidermis of WT and 35Spro-CRY1seedlings grown in continuous blue, red and far-red light, showing blue light-specific clustered stomata in 35Spro-CRY1. (Kang, C. et al., Plant Cell. 21: 2624-2641)