Light, temperature and circadian clock signal integration during leaf senescence

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Leaf senescence is a highly regulated process required for nutrient remobilisation in photosynthetically limited leaves. It occurs with age and in response to environmental stress. Dark-induced leaf senescence is regulated by the bHLH transcription factors, PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5 and is accelerated by high temperature. PIF4/5 abundance and activity are regulated by phytochromes, cryptochromes, temperature and the circadian clock. We have shown that low dose UV-B perceived by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8) promotes rapid PIF4/5 degradation through sequestration of the PIF-stabilising protein CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). UVR8 signalling additionally reduces PIF4/5 transcript abundance through an unknown mechanism, providing a highly effective dual target approach to supress PIF4/5 activity. Our unpublished work shows that pre- and postharvest UV-B treatment can supress the dark induction of senescence marker genes and reduce chlorophyll degradation in detached Arabidopsis leaves. Here, we propose to dissect the molecular mechanisms through which light, temperature and the circadian clock control leaf senescence and use this information to optimise preharvest treatment and postharvest storage of cut leaves. Characterisation of PIF4/5 circadian rhythms in detached leaves stored in the dark will guide the timings of postharvest light treatments for maximum senescence delay. RNA sequencing will additionally be used to identify novel PIF4/5-dependent and -independent targets involved in the suppression of leaf senescence by low temperature.