Nitric oxide negatively regulates abscisic acid signaling in guard cells by S-nitrosylation of OST1.
by Wang P., Du Y., Hou Y., Zhao Y., Hsu C., Yuan F., Zhu X., Tao W. A., Song C., Zhu J. (2015)
- Pengcheng Wanga,1,
- Yanyan Dua,b,1,
- Yueh-Ju Houa,
- Yang Zhaoa,c,
- Chuan-Chih Hsud,
- Feijuan Yuanb,
- Xiaohong Zhua,
- W. Andy Taod,
- Chun-Peng Songb, and
- Jian-Kang Zhua,c,2
in Proc Natl Acad Sci USA 112(2):613-618 – doi: 10.1073/pnas.1423481112 –
Drought stress induces the accumulation of the plant stress hormone abscisic acid (ABA). ABA then quickly activates the protein kinase OST1/SnRK2.6 to phosphorylate a number of proteins in guard cells, resulting in stomatal closure to reduce transpirational water loss. How SnRK2.6 is deactivated and how ABA signaling may be desensitized are unclear. This study found that nitric oxide (NO) resulting from ABA signaling causes S-nitrosylation of SnRK2.6 at a cysteine residue close to the kinase catalytic site, which blocks the kinase activity. Dysfunction of S-nitrosoglutathione (GSNO) reductase causes GSNO overaccumulation in guard cells and ABA insensitivity in stomatal regulation. This work thus reveals how ABA-induced NO functions in guard cells to inactivate SnRK2.6 to negatively feedback regulate ABA signaling.
The phytohormone abscisic acid (ABA) plays important roles in plant development and adaptation to environmental stress. ABA induces the production of nitric oxide (NO) in guard cells, but how NO regulates ABA signaling is not understood.
Here, we show that NO negatively regulates ABA signaling in guard cells by inhibiting open stomata 1 (OST1)/sucrose nonfermenting 1 (SNF1)-related protein kinase 2.6 (SnRK2.6) through S-nitrosylation.
We found that SnRK2.6 is S-nitrosylated at cysteine 137, a residue adjacent to the kinase catalytic site. Dysfunction in the S-nitrosoglutathione (GSNO) reductase (GSNOR) gene in the gsnor1-3 mutant causes NO overaccumulation in guard cells, constitutive S-nitrosylation of SnRK2.6, and impairment of ABA-induced stomatal closure.
Introduction of the Cys137 to Ser mutated SnRK2.6 into the gsnor1-3/ost1-3 double-mutant partially suppressed the effect of gsnor1-3 on ABA-induced stomatal closure.
A cysteine residue corresponding to Cys137 of SnRK2.6 is present in several yeast and human protein kinases and can be S-nitrosylated, suggesting that the S-nitrosylation may be an evolutionarily conserved mechanism for protein kinase regulation.