Phosphorylation regulation in two species of cold-hardy goldenrod gall insects.
The larvae of two cold-hardy insects, the freeze avoiding gall moth Epiblema scudderiana and freeze tolerant gall fly Eurosta solidaginis, endure prolonged exposures to subzero temperatures while overwintering. Both rely on a reduction in metabolic rate and the production of polyols for survival. The present study analyzed the role of several signal transduction enzymes in cold hardiness. Changes in cAMP-dependent protein kinase (PKA), protein phosphatases-1 (PP1), 2A, 2C and protein tyrosine phosphatase activities were monitored over the course of the winter season and also in insects exposed to -4C, -20C or anoxic conditions. The catalytic subunit of PKA (PKAc) and PP1 were purified to homogeneity from both species. Effects of low temperature on the enzymes included increased affinity of PKAc for the Kemptide substrate, and increased inhibition by okadaic acid of PP1. Differential regulation of kinases and phosphatases by low temperature appears to be key to regulating polyol production and, hence, cold survival.