Carbon Deprivation-Driven Transcriptome Reprogramming in Detached Developmentally Arresting Arabidopsis Inflorescences

Senescence is genetically-controlled and activated in mature tissues during ageing. However, immature plant tissues also display senescence-like symptoms when continuously exposed to adverse energy-depleting conditions. We used detached dark-held immature inflorescences of Arabidopsis thaliana to understand the metabolic reprogramming occurring in immature tissues transitioning from rapid growth to precocious senescence. Macroscopic growth of the detached inflorescences rapidly ceased upon placement in water in the dark at 21°C. Inflorescences were completely de-greened by 120 h of dark incubation and by 24 h had already lost 24% of their chlorophyll and 34% of their protein content. Comparative transcriptome profiling at 24 h revealed that inflorescences response at 24 h had a large carbon-deprivation component. Genes that positively regulate developmental senescence (ANAC092) and shade avoidance syndrome (PIF4 and PIF5) were up-regulated within 24 h. Mutations in these genes delayed de-greening of the inflorescences. Their up-regulation was suppressed in dark-held inflorescences by glucose treatment, which promoted macroscopic growth and development and inhibited de-greening of the inflorescences. Detached inflorescences held in the dark for 4 days were still able to re-initiate development to produce siliques upon being brought out to light indicating the transcriptional reprogramming at 24 h was adaptive and reversible. Our results suggest that the response of detached immature tissues to dark storage involves interactions between carbohydrate status sensing and light deprivation signaling and that the dark adaptive response of the tissues appears to utilize some of the same key regulators as developmental senescence.