Characterization of cDNAs representing five abscisic acid-responsive genes associated with somatic embryogenesis in Picea glauca, and their responses to abscisic acid stereostructure

Five abscisic acid (ABA)-responsive cDNAs that were identified by differential screening of a white spruce [Picea glauca (Moench) Voss] cotyledonary somatic embryo cDNA library are characterized. Three of the cDNAs (PgEMB12, 14, 15) are predicted to encode homologues of different late-embryogenesis-abundant (LEA) proteins, a further two (PgEMB 5 and 23) share little similarity to any known DNA or protein sequences. When suspension cultures were fed 1.5 x 10(5) M S-(+)-ABA and assessed for transcript abundance over 48 h, gene expression corresponding to each lea-like gene was inducible and was evident during the 48-h period. Conversely, transcripts were at a very low abundance when suspensions were fed R-(-)-ABA. When suspensions were treated with a range of S-(-)-ABA and R-(-)-ABA concentrations (10(-7)-10(-4) M), expression was induced at S-(+)-ABA concentrations of 10(-5) M, or above. Expression corresponding to PgEMB5 and PgEMB23 indicates less specificity for ABA stereostructure, with similar expression patterns being observed for either enantiomer during the 48 h after feeding. The two corresponding genes also appear more responsive to ABA concentration than the predicted lea genes, within the range examined (10(-7)-10(-4) M).