The control of germination by the PP2C family protein RDO5

Abstract

Dormancy provides a mechanism to prevent germination during unfavorable conditions, which is one of the most important process in higher plants. Apart from the phytohormones abscisic acid (ABA) and gibberellic acid (GA), two proteins namely DOG1 and RDO5 have been demonstrated to play an important role in controlling seed dormancy. DOG1 encodes a functionally unknown protein. Recent research revealed that DOG1 regulates seed dormancy by negatively regulating the actions of AHG1 and AHG3. Meanwhile, RDO5 was identified as another important factor in controlling seed dormancy. RDO5 does not contain phosphatase activity, which suggests that it might function as a pseudo-phosphatase. Phosphoproteomics analysis of the <em>rdo5</em> mutant showed a significant alternation in the phosphorylation level of several proteins, suggesting that RDO5 affects protein phosphorylation indirectly. RDO5 pull-down and mass spectrum experiments identified some RDO5 interacting proteins include DOG1, AHG1, CaM1 and CaM4. Protein interaction experiments further showed that RDO5 can form a complex with DOG1, AHG1, CaM1 and CaM4. Genetics evidence suggested that AHG1 and AHG3 are required for the function of RDO5 in the regulation of seed dormancy. Isotope experiments indicated that CaM1/4 and RDO5 may coordinate for the regulation of in seed dormancy via inhibition of AHG1 and AHG3 function. Moreover, the seed germination assays revealed that the double mutant <em>dog1 rdo5</em> showed similar ABA sensitivity as <em>dog1</em>, and <em>rdo5</em> is less sensitive, indicating that RDO5 may act upstream of DOG1 in seed dormancy. However, we still could not exclude the possibility that DOG1 functions through RDO5 and its homologs.