The Arabidopsis J protein AtJ1 is essential for seedling growth, flowering time control and ABA response.

We describe the in planta function of an Arabidopsis J protein gene, AtJ1. We isolated an ABA-hypersensitive mutant, named as793 (ABA-hypersensitive 793), by activation tagging screen. Analysis of the mutant revealed that T-DNA was inserted into the gene encoding AtJ1, thereby abolishing its expression. as793 plants grew very poorly under normal growth conditions; their seed setting efficiency was lower and their flowering was delayed compared with wild-type plants. Moreover, as793 plants were ABA hypersensitive and drought tolerant. In parallel analyses, we found that another AtJ1 knockout mutant acquired from the Arabidopsis Stock Center exhibited the same phenotypes as as793 and that its phenotypes could be complemented by the wild-type AtJ1. At the molecular level, we found that the expression of a large number of genes involved in embryogenesis, flowering time control and stress response was altered in as793. Others previously reported that AtJ1 is a mitochondrial protein involved in thermotolerance. Our results further indicate that AtJ1 is essential for normal plant growth, from embryogenesis to flowering and seed setting. Additionally, the ABA hypersensitivity of as793 suggests that AtJ1 may function as a negative regulator of ABA response.