Induction and regulation of heat-shock gene expression by an amino acid analog in soybean seedlings

The effect of the proline analog azetidine-2-carboxylic acid (Ate) on the induction and the regulation of heat-shock (HS) mRNA accumulation and heat-shock protein (HSP) synthesis in soybean (Glycine max) seedlings was studied. Treatment with Ate elicited an HS-like response at the normal growth temperature, 28 degrees C, with seven of nine HS cDNA clones tested. Two cDNA clones, GmHsp22.5 and pFS2033, share 78% identity; however, transcripts hybridizing to GmHsp22.5 but not pFS2033 accumulated with Ate treatment at 28 degrees C. Substantial incorporation of radioactive amino acid into high molecular weight HSPs but not low molecular weight HSPs was observed in vivo during Ate treatment at 28 degrees C. Low molecular weight HSPs were detected using antibodies raised against an abundant member of low molecular weight class I HSPs, indicating that low molecular weight HSPs were synthesized at normal growth temperatures during Ate treatment despite a lack of substantial in vivo radioactive amino acid incorporation. In summary, Ate treatment induced accumulation of most but not all HS mRNAs and HSPs in soybean seedlings; the observations presented here suggest differential regulation among various HS genes at the transcriptional and posttranscriptional levels.