Abstract
To elucidate the molecular mechanisms of stomatal opening and closure, we performed a genetic screen using infrared thermography to isolate stomatal aperture mutants. We identified a mutant designated low temperature with open-stomata 1 (lost1), which exhibited reduced leaf temperature, wider stomatal aperture, and a pale green phenotype. Map-based analysis of the LOST1 locus revealed that the lost1 mutant resulted from a missense mutation in the Mg-chelatase I subunit 1 (CHLI1) gene, which encodes a subunit of the Mg-chelatase complex involved in chlorophyll synthesis. Transformation of the wild-type CHLI1 gene into lost1 complemented all lost1 phenotypes. Stomata in lost1 exhibited a partial ABA-insensitive phenotype similar to that of rtl1, a Mg-chelatase H subunit missense mutant. The Mg-protoporphyrin IX methyltransferase (CHLM) gene encodes a subsequent enzyme in the chlorophyll synthesis pathway. We examined stomatal movement in a CHLM knockdown mutant, chlm, and found that it also exhibited an ABA-insensitive phenotype. However, lost1 and chlm seedlings all showed normal expression of ABA-induced genes, such as RAB18 and RD29B, in response to ABA. These results suggest that the chlorophyll synthesis enzymes, Mg-chelatase complex and CHLM, specifically affect ABA signaling in the control of stomatal aperture and have no effect on ABA-induced gene expression.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-014-0636-0) contains supplementary material, which is available to authorized users.
Highlights
Stomatal pores in the plant epidermis, each surrounded by a pair of guard cells, regulate gas exchange between plants and the atmosphere to control processes such as CO2 uptake for photosynthesis and transpiration for water loss regulation (Shimazaki et al 2007)
Kinoshita (&) Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya 464-8602, Japan e-mail: kinoshita@bio.nagoya-u.ac.jp normal expression of abscisic acid (ABA)-induced genes, such as RAB18 and RD29B, in response to ABA. These results suggest that the chlorophyll synthesis enzymes, Mg-chelatase complex and CHLM, affect ABA signaling in the control of stomatal aperture and have no effect on ABAinduced gene expression
The lost1 mutant contained an Arg219 to Lys missense mutation in Mg-chelatase I subunit 1 (CHLI1) and showed a partial ABA-insensitive phenotype for stomatal movement and reduced chlorophyll content
Summary
Stomatal pores in the plant epidermis, each surrounded by a pair of guard cells, regulate gas exchange between plants and the atmosphere to control processes such as CO2 uptake for photosynthesis and transpiration for water loss regulation (Shimazaki et al 2007). ABA has been suggested to activate SLOW ANION CHANNELASSOCIATED 1 (SLAC1), which is thought to be a slowtype anion channel (Negi et al 2008; Vahisalu et al 2008), via PYR/PYL/RCAR-PP2Cs-SnRK2 modules followed by depolarization of the plasma membrane (Geiger et al 2009; Lee et al 2009). In addition to PYR/PYL/RCAR, several candidate ABA receptors have been reported including the Mg-chelatase H subunit (CHLH) (Du et al 2012; Shen et al 2006; Wu et al 2009), G-protein coupled receptor 2 (GCR2) (Liu et al 2007), and G-protein coupled receptortype G proteins (GTG1 and GTG2) (Pandey et al 2009). GCR2 is controversial (Klingler et al 2010)
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