Sucrose synthase interaction with voltage‐dependent anion channel suggests a potential role for the enzyme in inter‐organellar signaling

Abstract

Sucrose synthase (SUS) is a key enzyme in plant sucrose catabolism. Our recent work indicates that the biological function of SUS extends beyond its biochemical activity. This inference is based on a) tissue- & isoform-specific association of SUS with mitochondria and b) isoform-specific & anoxia-responsive interaction of SUS with the voltage-dependent anion channel (VDAC). Here we show that both VDAC & SUS are also localized to the nucleus and inversely regulated in these two compartments under anoxic stress. SUS localizes to nuclei in a tissue- & isoform-specific and anoxia-enhanced manner. Unlike in mitochondria where the protein is mostly a monomer, SUS occurs as an oligomer in the nuclei. VDAC exists in a dynamic equilibrium of mono-& oligomers and is de-oligomerized under anoxia, indicating that oligomerization is needed for its normal aerobic function. VDAC also forms supramolecular complexes both in mitochondria & nuclei. Immuno-affinity chromatography indicates that the composition of these complexes is altered under anoxia. The de-oligomerization of VDAC induced under anoxia seems to cause a movement of VDAC & SUS from mitochondria to the nucleus. This shuttling of the proteins temporally coincides with the initiation of cell death in anoxic maize tissues. We propose that the inter-compartmental movement of SUS & VDAC may report the energy crisis to the nuclei and signal the activation of the cell death pathway.