Editors' ChoicePlant biology

More Roles for Cryptochromes

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Science Signaling  17 Feb 2009:
Vol. 2, Issue 58, pp. ec61
DOI: 10.1126/scisignal.258ec61

Cryptochromes (CRYs) are proteins that sense blue light, and in plants these proteins play important roles in regulating growth, development, and circadian responses. Xu et al. identified two cryptochrome genes in wheat, TaCRY1a and TaCRY2, and characterized the structure and function of these proteins. Some CRY proteins exhibit light-induced nucleocytoplasmic shuttling. TaCRY2 contained a putative nuclear localization signal; expression of a green fluorescent protein (GFP) fusion protein showed that TaCRY2 was restricted to the nucleus in the dark and that, when exposed to blue light, the signal for TaCRY2 disappeared, suggesting that it was degraded in a light-dependent manner. In contrast, TaCRY1a did not have a consensus nuclear localization or nuclear export signal. A GFP fusion protein with TaCRY1a revealed that, in the dark, this protein was localized to the nucleus and along the inner cell wall, suggesting association with the plasma membrane. In response to blue light, TaCRY1a moved from the plasma membrane and nucleus and became diffusely located in the cytoplasm. Reverse transcription polymerase chain reaction (RT-PCR) experiments revealed that TaCRY1a and TaCRY2 were both expressed in seedling leaves and roots, as well as in germinating embryos. TaCRY1a transcripts were more abundant in leaves than in roots or embryos, and TaCRY2 showed the inverse pattern. RT-PCR showed that when seedlings or germinating embryos were exposed to osmotic stress (high salt or polyethylene glycol), within 12 hours TaCRY2 expression was repressed in leaves and increased in seedling roots and germinating embryos. In contrast, TaCRY1a expression was unchanged until 24 hours of osmotic stress, at which time expression of TaCRY1a in roots was increased. Abscisic acid (ABA) is a hormone produced in response to stress, and application of ABA to seedling roots or germinating embryos stimulated the transcription of TaCRY2. Transgenic Arabidopsis plants overexpressing TaCRY1a-GFP or TaCRY2-GFP were more severely affected by osmotic stress or ABA than were wild-type plants. These experiments suggest that CRYs have roles beyond those of responding to light, and it may be that light affects plant sensitivity to stress by crosstalk mediated at the CRYs.

P. Xu, Y. Xiang, H. Zhu, H. Xu, Z. Zhang, C. Zhang, L. Zhang, Z. Ma, Wheat cryptochromes: Subcellular localization and involvement in photomorphogenesis and osmotic stress responses. Plant Physiol. 149, 760–774 (2009). [Abstract] [Full Text]

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