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 (Aze) 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 Aze elicited an HS-like response at the normal growth temperature, 28[deg]C, with seven of nine HS cDNA clones tested. Two cDNA clones, Gm-Hsp22.5 and pFS2033, share 78% identity; however, transcripts hybridizing to GmHsp22.5 but not pFS2033 accumulated with Aze treatment at 28[deg]C. Substantial incorporation of radioactive amino acid into high molecular weight HSPs but not low molecular weight HSPs was observed in vivo during Aze treatment at 28[deg]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 Aze treatment despite a lack of substantial in vivo radioactive amino acid incorporation. In summary, Aze 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.