Overexpression of DnaK chaperone from a halotolerant cyanobacterium Aphanothece halophytica increases seed yield in rice and tobacco

The DnaK/Hsp70 family is a molecular chaperone that binds non-native states of other proteins, and concerns to various physiological processes in the bacterial, plant and animal cells. Transgenic tobacco plants expressing a molecular chaperone DnaK from a halotolerant cyanobacterium Aphanothece halophytica show enhanced seed yields as well as enhanced tolerances for salt and heat stresses. High-temperature treatment during the reproductive stage decreased total dry weight of seeds in both transgenic and wild-type tobacco, but more severely in the wild-type. Transgenic tobacco plants exhibited higher activities of ascorbate peroxidase and catalase than wild-type plants. Similar results were obtained for salt stress during the reproductive stage. Transgenic rice plants expressing ApDnaK was also constructed. Transgenic rice plants exhibited the enhanced activities for Calvin-cycle enzymes, and showed faster growth and higher seed yield compared with the wild-type rice under normal growth conditions. Transgenic rice plants also showed enhanced tolerance for high temperature and salt stress compared with the wild-type rice. These results suggest a relation of increased folding activity with enhanced stress tolerance, increased seed yield, and total plant biomass.