Chloroplast-to-Nucleus Communication and Drought Stress Signalling

Retrograde communication from organelles to the nucleus, using several small metabolites as signalling molecules, can convey oxidative stress occurring in organelles to the nucleus for activation of acclimation responses.

One such metabolite signal, 3’-phosphoadenosine 5’-phosphate (PAP), normally degraded by a phosphatase SAL1 under constitutive conditions, accumulates to high levels under abiotic stresses such as drought and high light. PAP activates the expression of multiple stress-responsive genes by altering RNA metabolism thereby conferring drought tolerance when over-accumulated.  Some central questions pertaining to chloroplast signals such as PAP are the structural-biochemical regulation, physiological, and evolutionary aspects of such signalling pathways.

In this talk Dr Chan will present his recent findings on how oxidative stress sensing in organelles enables PAP signalling, which participates in guard cell regulation in an evolutionarily conserved manner.

Finally, Dr Chan will present unpublished data where researchers have taken inspiration from drug-discovery approaches and performed a large-scale chemical genomics screen on 20,000 small molecules for SAL1 inhibitors. In-depth characterization on 100 putative hits with  molecular dynamics simulations and biochemical studies revealed a key regulatory loop on the enzyme and provided insights into how SAL1 activity can be regulated at the structural level by metabolite-protein interactions.

Significantly, these inhibitors are active in vivo and can target SAL1 enzymes from multiple species; thereby providing the possibility for rationally designing chemical modulators of SAL-mediated chloroplast signalling in plants. The findings illustrate how organelle communication pathways can be integrated into cellular signalling networks, and provide new targets for engineering drought-proof plants.

Dr Kai Xun Chan is a Postdoctoral Fellow at the VIB-UGent Center for Plant Systems Biology at Ghent University, Belgium, and the Center of Excellence in Plant Energy Biology, The Australian National University, Canberra.