The Organization and Evolution of the Spinach Stress 70 Molecular Chaperone Gene Family

The stress 70 molecular chaperones of plants are localized and function in all of the major subcellular compartments of the cell. Collectively, all of the various forms are encoded by a multigene family in the nucleus. At least 12 members of this family have been found, and sequence and DNA blot analyses provide an emerging description of the diversity of gene structure organization for this family of evolutionarily conserved proteins in spinach. They exhibit not only structural diversity in the organization of coding and noncoding regions but also distinct expression patterns for different tissues and abiotic conditions. The results of phylogenetic analyses are concordant with at least four major evolutionary events that gave rise to stress 70 molecular chaperones in each of four major subcellular compartments of plant cells: the plastid, mitochondrion, cytoplasm, and endoplasmic reticulum. The varied expression patterns also illustrate the complexity of effectively interpreting the role of any one of these stress-related proteins in response to abiotic stress in the absence of context to the other members of the family.