Phytochrome signaling regulates dark-induced senescence in plants
Plants sense light as information and energy and adapt themselves to available environmental light conditions. A plant leaf kills itself when it does not sense light for a few days. Although phytochrome was likely to be involved in the suicide phenomenon, the underlying mechanism was not understood.
Leaves of green plants normally live for many weeks; however, in darkness, leaves turn yellow and die within a few days. Presumably, plants sacrifice leaves that cannot efficiently conduct photosynthesis, and relocate their nutrients to growing leaves. Here, we reveal the molecular mechanism underpinning this phenomenon. Although the plant light sensor phytochrome was known to be involved in the senescence, a downstream pathway was not understood. In collaboration with researchers at Seoul National University, the detailed signaling cascades from light perception by phytochrome to a key senescence gene expression was demonstrated. Various phytochrome signaling mutants were screened and transcription factors called Phytochrome-Interacting Factors (PIFs) were revealed and are responsible for senescence regulation. To find further signaling pathways, various microarray and chromatin immunoprecipitation-sequencing data was analyzed to find which transcriptional targets of PIFs could regulate senescence. As a result, it was revealed that PIFs induce a key senescence gene called ORESARA1 (meaning ‘long-lived’ in the Korean language), and that a mutant plant lacking ORESARA1 showed delayed senescence under darkness.
In prolonged darkness, PIF proteins accumulate and increase the expression of ORESARA1 which initiates leaf yellowing, cellular nutrient export, and finally leads to apoptosis.
In light, phytochrome destabilizes PIF proteins, preventing leaf death. These findings provide new insights on how plants actively regulate leaf lifespan to optimize their survival in nature.
Related article: Sakuraba et al. Nature Communications 5, Article number: 4636 (published August 2014)
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