Involvement of Arabidopsis NAC transcription factor in the regulation of 20S and 26S proteasomes.

We investigated the transcript levels of 13 proteasome subunit genes, the protein levels of proteasomes, and the activities of the 26S proteasome in ANAC078-overexpressing Arabidopsis plants (Ox-ANAC078) and knockout ANAC078 (KO-ANAC078) mutants. The transcript levels and the protein levels of proteasomes were increased in the Ox-ANAC078 plants compared with the wild-type plants and KO-ANAC078 mutants under normal conditions and high-light (HL) stress. Although the activities of the 26S proteasome were decreased in all the plants under HL stress, they were higher in the Ox-ANAC078 plants than wild-type plants and KO-ANAC078 mutants under normal conditions and HL stress. These findings suggest that ANAC078 regulates the levels of proteasomes. To explore the function of the increased levels of proteasomes to HL stress, we assessed the tolerance to HL stress of the Ox-ANAC078 plants and KO-ANAC078 mutants. The photosystem II activities of Ox-ANAC078 remained high compared with those of the wild-type plants and KO-ANAC078 mutants under HL stress, suggesting that ANAC078 may play an important role in the response and adaptation to HL stress.