SLR/IAA14 and ARF7/19 are differently involved in galactolipid and sulfolipid syntheses during phosphate starvation

Abstract

During phosphate (Pi) starvation, galactolipid digalactosyldiacylglycerol (DGDG) and sulfolipid sulfoquinovosyldiacylglycerol (SQDG) increase concomitantly with a decrease in phospholipids. Recently, we reported that auxin is involved in the DGDG accumulation during Pi starvation. SLR/IAA14 is one of the IAA proteins and represses at least two AUXIN RESPONSE FACTOR (ARF) proteins, ARF7 and ARF19. Here, we revealed that DGDG and SQDG accumulation upon Pi starvation was suppressed in the gain-of-function mutant slr and loss-of-function mutant arf7arf19. We also examined the level of gene expression for type B monogalactosyldiacylglycerol synthases (MGD2/3) and sulfoquinovosyldiacylglycerol synthases (SQD1/2) in these mutants. Both expressions were suppressed upon Pi-starved conditions in the mutants. Although SQD1/2 were not suppressed in Pi-sufficient conditions of slr and arf7arf19, MGD2/3 were suppressed in the conditions. Thus, auxin is differently involved in galactolipid and sufolipid syntheses under Pi starvation.