Highly Homologous RING domain 1（AtHHR1）encodes a RING finger E3 ligase. It may play a role in participating heat stress response, according to publically available microarray data. To study the function of AtHHR1 under heat stress, 3 homozygous complementary transgenic lines athhr1/ATHHR1 were identified. The mutants, complementary transgenic lines and wild-type of Arabidopsis were used for heat stress experiment. Under the treatment of heat stress, the germination rate and relative chlorophyll and proline contents in mutant plants were higher than that in wild-type, while those in the complementary transgenic plants were all lower than that in wild-type. After heat stress, the expression levels of heat-related genes were higher in the mutant plants than in the wild-type. These results suggested that AtHHR1 gene played a negative regulatory role in Arabidopsis thaliana thermotolerance．
