Blue light triggers the opening of stomata in the morning to allow CO2 uptake and water loss through transpiration. During the day, plants may experience periodic drought and accumulate abscisic acid (ABA). ABA antagonizes blue light signalling through phosphatidic acid and reduces stomatal aperture. This study reveals a molecular mechanism by which two light signalling proteins interact to repress ABA signalling in the control of stomatal aperture. A hypersensitive to red and blue 2 (hrb2) mutant has a defective ATP-dependent chromatin-remodelling factor, PKL, in the chromodomain/helicase/DNA binding family. HRB2 enhances the light-induced expression of a B-box transcription factor gene, BBX21. BBX21 binds a T/G box in the ABI5 promoter and recruits HRB2 to modulate the chromatin structure at the ABI5 locus. Mutation in either HRB2 or BBX21 led to reduced water loss and ABA hypersensitivity. This hypersensitivity to ABA was well explained by the enhanced expression of the ABA signalling gene ABI5 in both mutants. Indeed, stomatal aperture was significantly reduced by ABI5 overexpression in the absence or presence of ABA under monochromatic light conditions. Overall, we present a regulatory loop in which two light signalling proteins repress ABA signalling to sustain gas exchange when plants experience periodic drought.
Bibliographical noteFunding Information:
We are grateful to Dr. Xingwang Deng for providing hy5‐215, hy5/hyh, bbx21‐1, and abi5‐1 mutants, and 35S::HA:HY5, 35S::MYC:BBX21, and 35S::YFP:BBX21 transgenic seeds. We are also grateful to Dr. Ogas for the pkl‐1 mutant, Dr. Qi Xu for the ABI5‐OX lines, Dr. Rongcheng Lin for the antibodies against PKL and tubulin and pLacZi2μ Y1H vector, Dr. Tatsuo Kakimoto for the PKL full‐length, N‐terminus, and C‐terminus Y2H vectors, and Dr. Claudia Köhler for the pPKL::PKL:GFP construct. This work was supported by grants from the National Science Foundation (MCB 1021645 to M.N. and IIS 1149697 to R.K.). Gang Xu was supported by a grant from National Natural Science Foundation of China (31470379). The authors declare that they have no conflicts of interest.
Division of Molecular and Cellular Biosciences, Grant/Award Number: MCB 1021645; National Natural Science Foundation of China, Grant/Award Number: 31470379; National Science Foundation, Grant/Award Numbers: IIS 1149697 and MCB 1021645
© 2018 John Wiley & Sons Ltd
- ABA signalling
- light quality