Professor Hong Kong Baptist University Hong Kong, Hong Kong
Body of Abstract: Using thermoimaging screening, we isolated an Arabidopsis lot1(lower temperature 1) mutant that showed increased leaf transpiration under drought stress conditions. The lot1 mutant is less responsive to ABA-induced stomata closure and was proposed to function in regulating the trafficking of C2-domian ABA-related proteins (CAR) (Qin et al., 2019. Mol Plant 12: 1243). To further understanding the modes of action for LOT1, yeast two-hybrid screens and immunoprecipitation assays were performed to identify LOT1 interacting proteins. Among the interacting proteins was a PARG (poly ADP-ribose glycohydrolase) protein. It was found that the PARG protein interacts with LOT1 in the nucleus and this interaction affects protein PARylation levels. In vitro assays showed that LOT1 inhibits PARG activity through protein-protein interaction. The lot1 mutant has overall reduced levels of PARylation, whereas overexpression of LOT1 increases protein PARylation, consistent with the inhibitory effect of LOT1 on PARG activity. The PARylation level in the lot1 parg double mutant is similar to that of the single mutants, suggesting that LOT1 and PARG may function in the same pathway in regulating PARylation and ABA responses. Like in the lot1 mutant, less CAR9 was relocated from the nucleus to the plasma membrane upon ABA treatment. Consistently, parg1 was drought-sensitive, similar as lot1. Stomata of the parg mutant were also less responsive to ABA in inducing closure. The mechanisms involved in PARylation of ABA signaling components are under investigation. This study was supported by Research Grants Council (RGC) of Hong Kong (Grant #GRF 12103020) to LX.