Abstract
During phosphate starvation, membrane galactolipid digalactosyldiacylglycerol (DGDG) accumulates concomitantly with a decrease in phospholipids. Recently, we revealed that auxin is involved in this process. Auxin signaling is activated by degradation of IAA proteins that bind directly AUXIN RESPONSE FACTOR (ARF) and thus inhibit transcription of ARF-regulated auxin responsive genes. SLR is one of the IAA proteins, and ARF7 and ARF19 are known to interact with SLR. Here, we revealed that DGDG accumulation upon phosphate starvation was suppressed in the gain-of-function mutant slr and loss-of-function mutant arf7arf19. During phosphate starvation, DGDG ratio of total polar lipids was increased up to 35% although its ratio was about 20% under phosphate-sufficient conditions in Arabidopsis shoot. In slr and arf7arf19, however, the DGDG increase by phosphate starvation was suppressed to 25% and 30%, respectively. These results indicate the involvement of the auxin signaling proteins in substitution of phospholipids to galactolipids during phosphate starvation.
