Expression of DnaJ homologs and Hsp70 in the Japanese willow (Salix gilgiana Seemen)

Abstract

We isolated three cDNA clones (pSGJ1, pSGJ2 and pSGJ3) for DnaJ-like proteins of the Japanese willow (Salix gilgiana Seemen). The insert in pSGJ2 included the entire nucleotide sequence of the insert in pSGJ1 that was separated into four parts by three intron-like sequences, and it might correspond to the cDNA for a precursor to the SGJ1 mRNA. The predicted amino acid sequences of SGJ1 (47.5 kDa) and SGJ3 (46.6 kDa) exhibited about 70 to 91% homology to plant cytoplasmic DnaJ-like proteins. SGJ1 was encoded by one or a few genes within the willow genome while SGJ3 was encoded by several genes. Expression of the SGJ1 and SGJ3 genes was compared with that of Hsp70 (SGK1) gene. Constitutive expression of SGJ1, SGJ3 and SGK1 was detected in all organs examined. The SGJ1 mRNA was most abundant in male catkins (inflorescences). High-level expression of SGJ3 and SGK1 was detected in catkins and roots of both male and female plants. The level of the SGJ3 mRNA in the leaves increased about 10-fold after 1 h of heat stress while the expression of SGJ1 mRNA reached a maximum level after 6 h. However, the extent of induction of SGJ1 mRNA was quite low. The levels of SGJ1 and SGJ3 mRNAs in the leaves increased about 6-fold and 2-fold, respectively, after 24 h of treatment with 100 mM NaCl. Thus, the SGJ1 and SGJ3 genes showed differential expression patterns in a variety of organs and in response to different environmental conditions.