期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：47
DOI：10.1073/pnas.2107280118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
With the continuing increase in global temperatures, plants transpire more water due to the increasing vapor pressure deficit. Stomatal pores in plants close rapidly in response to the rising vapor pressure deficit to counteract water loss. We demonstrate that mutations in the stomatal CO
2 signaling pathway do not impair the response to an increase in vapor pressure difference (VPD). Osmotic stress causes cytoplasmic Ca
2+ transients in guard cells. Nevertheless, we show that diverse investigated higher-order calcium-signaling mutants do not affect the VPD response. We reveal that B3 family Raf-like protein kinases and a plasma membrane receptor-like protein GHR1 function in the elusive leaf-to-air VPD-mediated stomatal closure pathway. Notably,
ghr1 mutant alleles disrupt the classical “wrong-way” stomatal VPD response.
Stomatal pores close rapidly in response to low-air-humidity-induced leaf-to-air vapor pressure difference (VPD) increases, thereby reducing excessive water loss. The hydroactive signal-transduction mechanisms mediating high VPD–induced stomatal closure remain largely unknown. The kinetics of stomatal high-VPD responses were investigated by using time-resolved gas-exchange analyses of higher-order mutants in guard-cell signal-transduction branches. We show that the slow-type anion channel SLAC1 plays a relatively more substantial role than the rapid-type anion channel ALMT12/QUAC1 in stomatal VPD signaling. VPD-induced stomatal closure is not affected in
mpk12/
mpk4GC double mutants that completely disrupt stomatal CO
2 signaling, indicating that VPD signaling is independent of the early CO
2 signal-transduction pathway. Calcium imaging shows that osmotic stress causes cytoplasmic Ca
2+ transients in guard cells. Nevertheless,
osca1-2/
1.3/
2.2/
2.3/
3.1 Ca
2+-permeable channel quintuple,
osca1.3/
1.7-channel double,
cngc5/
6-channel double,
cngc20-channel single,
cngc19/
20crispr-channel double,
glr3.2/
3.3-channel double,
cpk-kinase quintuple,
cbl1/
4/
5/
8/
9 quintuple, and
cbl2/
3rf double mutants showed wild-type-like stomatal VPD responses. A B3-family Raf-like mitogen-activated protein (MAP)-kinase kinase kinase, M3Kδ5/RAF6, activates the OST1/SnRK2.6 kinase in plant cells. Interestingly, B3 Raf-kinase
m3kδ5 and
m3kδ1/
δ5/
δ6/
δ7 (
raf3/
6/
5/
4) quadruple mutants, but not a 14-gene
raf-kinase mutant including osmotic stress-linked B4-family Raf-kinases, exhibited slowed high-VPD responses, suggesting that B3-family Raf-kinases play an important role in stomatal VPD signaling. Moreover, high VPD–induced stomatal closure was impaired in receptor-like pseudokinase GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1) mutant alleles. Notably, the classical transient “wrong-way” VPD response was absent in
ghr1 mutant alleles. These findings reveal genes and signaling mechanisms in the elusive high VPD–induced stomatal closing response pathway.
