Vacuolar processing enzyme activates programmed cell death in the apical meristem inducing loss of apical dominance

The potato (Solanum tuberosum L.) tuber is a swollen underground stem that can sprout in an apical dominance (AD) pattern. Bromoethane (BE) induces loss of AD and the accumulation of vegetative vacuolar processing enzyme (S. tuberosum vacuolar processing enzyme [StVPE]) in the tuber apical meristem (TAM). Vacuolar processing enzyme activity, induced by BE, is followed by programmed cell death in the TAM. In this study, we found that the mature StVPE1 (mVPE) protein exhibits specific activity for caspase 1, but not caspase 3 substrates. Optimal activity of mVPE was achieved at acidic pH, consistent with localization of StVPE1 to the vacuole, at the edge of the TAM. Downregulation of StVPE1 by RNA interference resulted in reduced stem branching and retained AD in tubers treated with BE. Overexpression of StVPE1 fused to green fluorescent protein showed enhanced stem branching after BE treatment. Our data suggest that, following stress, induction of StVPE1 in the TAM induces AD loss and stem branching. Solanum tuberosum vacuolar processing enzyme (StVPE) is shown to be associated with programmed cell death leading to loss of apical dominance and the uses of vacuolar processing enzyme inhibitors restore apical dominance. We present new evidence demonstrating the enzyme substrate specificity optimal activity and cellular localization following stress. We present for the first time functional involvement of StVPE1 in stem apical dominance by studying overexpression and vacuolar processing enzyme RNA‐interference‐inhibited transgenic lines. These findings provide new insights into the role of vacuolar processing enzyme in stem apical dominance.