Regulation of a wheat actin-depolymerizing factor during cold acclimation

We have previously shown that the wheat (Triticum avestivum) TaADF gene exp ression level is correlated with the plants capacity to tolerate freezing. Sequence analysis revealed that this gene encodes a protein homologous to m embers of the actin-depolymerizing factor (ADF)/cofilin family. We report h ere on the characterization of the recombinant TaADF protein. Assays for AD F activity showed that TaADF is capable of sequestering actin, preventing n ucleotide exchange, and inducing actin depolymerization. In vitro phosphory lation studies showed that TaADF is a substrate for a wheat 52-kD kinase. T he activity of this kinase is modulated by low temperature during the accli mation period. Western-blot analyses revealed that TaADF is expressed only in cold-acclimated Graminene species and that the accumulation level is muc h higher in the freezing-tolerant wheat cultivars compared with the less to lerant ones. This accumulation was found to be regulated by a factor(s) enc oded by a gene(s) located on chromosome 5A, the chromosome most often found to be associated with cold hardiness. The induction of an active ADF durin g cold acclimation and the correlation with. an increased freezing toleranc e suggest that the protein may be required for the cytoskeletal rearrangeme nts that may occur upon low temperature exposure. These remodelings might b e important for the enhancement of freezing tolerance.