Plant U-box armadillo repeat proteins AtPUB18 and AtPUB19 are involved in salt inhibition of germination in Arabidopsis

Plant U-box armadillo repeat (PUB-ARM) proteins represent a type of E3 ubiquitin ligase. PUB-ARM proteins have various functions in plant development, plant defence and plant stress responses. The so far uncharacterised PUB-ARM proteins AtPUB18 and AtPUB19 are highly homologous to each other and regulated on the transcript level by ABA and NaCl. To investigate their physiological function, we isolated and characterised two Arabidopsis mutants and named them pub18-1 and pub19-1. However, these single mutants did not show any ABA-or salt-dependent phenotype. In contrast, pub18-1/pub19-1 double mutant seeds were less sensitive to ABA and NaCl inhibition of seed germination compared to wild-type seeds, indicating that both PUB-ARM proteins may coordinately function as regulatory components in ABA or salt inhibition of germination.