OPEN STOMATA3 - an ABC transporter implicated in ABA signalling, drought and light response

Wasilewska, Aleksandra and Riera, Marta and Valon, Christiane and Giraudat, Jérôme and Merlot, Sylvain and Blatt, Michael R. and Sutter, Jens Uwe and Leung, Jeffrey (2008) OPEN STOMATA3 - an ABC transporter implicated in ABA signalling, drought and light response. In: European Plant Science Organisation Conference, 2008-06-22 - 2008-06-26.

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    Abstract

    Mutants sensitive to progressive water deficit are characterized by excessive transpiration due to the failure of stomatal closure and can therefore be detected as cold plants (Fig. 1 blue) by remote infrared imaging (Merlot et al., 2002). Among the signalling mutants, three are collectively named open stomata (ost). The corresponding OST1 and OST2 genes encode an ABA-activated kinase and a P-type H+-ATPase, respectively (Mustilli et al., 2002; Merlot et al., 2007). The current work deals with OST3 which encodes an ATP-binding cassette (ABC) transporter. There are over 120 members of the ABC protein in the superfamily of Arabidopsis thaliana. Most of them are membrane-bound proteins that transport a diverse range of substances across the phospholipid bilayer. Characterisation of the mutant phenotype confirmed that ost3 transpires excessively (Fig. 1, 2). We have also shown that the ost3 mutations reduce seed dormancy (Fig. 3) but seed sensitivity to exogenous ABA seems unaffected (data not shown). The guard cells of ost3 are impaired in responses to ABA and light (Fig. 4), but are normal with respect to low level of CO2 which stimulates stomatal opening (data not shown). OST3 is expressed mainly in leaves, particularly in guard cells (Fig. 5), but it is low in root tissues. Transgenic expression of the OST3 protein fused to GFP in the ost3 mutant can rescue the phenotype and moreover, the fusion protein is targeted exclusively to the plasma membrane (Fig. 6) suggesting that it has a role in intercellular transport required for ABA signal perception. We found that OST3 interacts with OST2 (Fig. 8) and OST1 (Fig. 8 + 9). The last observation is also consistent with the fact that OST3 can be phosphorylated by OST1 in vitro (Fig. 7). Therefore we suggest that the trio of proteins identified by our genetic screen may function in the same signalling complex in mediating stomatal response.