The NAC transcription factor ATAF2 enhances Arabidopsis biomass and chlorophyll a accumulations at the early growth stage.

Objective: The Arabidopsis thaliana NAC-family transcription factor ATAF2 plays extensive regulatory roles in plant disease resistance, abiotic stress tolerance, leaf senescence, hormone metabolism, and seedling photomorphogenesis. Using Arabidopsis seedlings as the investigation platform, we previously demonstrated that ATAF2 overexpression can increase the endogenous levels of the growth-promoting hormone brassinosteroids (BRs) and suppress the expression of the chlorophyll b (Chl-b) reductase NYC1, which catalyzes the initial step of the degradation of light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII). ATAF2 also promotes the expression of NIT2, which is involved in the biosynthesis of the auxin indole-3-acetic acid (IAA). Here, we further examined the effects of elevated BR/IAA levels and reduced NYC1 expression on biomass and Chl-a/b accumulations, respectively.

Results: Twelve-day-old plants were harvested for biomass and Chl-a/b measurements. While no significant difference of biomass or Chl-a/b accumulations was observed between the wild-type Col-0 and the loss-of-function ataf2-1/2 plants, all three ATAF2 overexpression lines (ATAF2ox-1/2/3) exhibited much higher biomass and Chl-a accumulations as compared to Col-0 and ataf2-1/2, which can at least be partially interpreted as the consequences of higher endogenous BR/IAA levels and reduced NYC1 expression, respectively. The results demonstrate the positive regulatory role of ATAF2 in biomass and Chl-a accumulations. Notably, ATAF2 overexpression does not increase Arabidopsis biomass accumulation at later growth stages, indicating its functional nature of developmental timing acceleration.