Competitive inhibition of abscisic acid-regulated gene expression by stereoisomeric acetylenic analogs of abscisic acid

• Published in: Plant physiology (Bethesda) 1993-02, Vol.101 (2), p.469-476
• Main Authors: Wilen, R.W, Hays, D.B, Mandel, R.M, Abrams, S.R, Moloney, M.M
• Format: Article
• Language: English
• Subjects: ACIDE ABSCISSIQUE; ACIDO ABSCISICO; Agonists; Biological and medical sciences; Biosynthesis; BRASSICA NAPUS; CHIMIE; Complementary DNA; EMBRIONES VEGETALES; EMBRYON VEGETAL; Embryos; Enantiomers; EXPRESION GENICA; EXPRESSION DES GENES; Fundamental and applied biological sciences. Psychology; Gene expression; Gene expression regulation; Growth regulators; INHIBIDORES DEL CRECIMIENTO; Metabolism; Molecular Biology and Gene Regulation; Plant physiology and development; PRESION OSMOTICA; PRESSION OSMOTIQUE; PROTEINAS VEGETALES; PROTEINE VEGETALE; QUIMICA; RETARDATEUR DE CROISSANCE; RNA; Stereochemistry; Storage proteins
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.101.2.469

The properties of two enantiomeric synthetic acetylenic abscisic acid (ABA) analogs (PBI-51 and PBI-63) in relation to ABA-sensitive gene expression are reported. Using microspore-derived embryos of Brassica napus as the biological material and their responsiveness to ABA in the expression of genes encoding storage proteins as a quantitative bioassay, we measured the biological activity of PBI-51 and PBI-63. Assays to evaluate agonistic activity of either compound applied individually showed a dose-dependent increase in napin gene expression on application of PBI-63. Maximal activity of about 40 micromolar indicated that PBI-63 was an agonist, although somewhat weaker than ABA. PBI-63 has a similar stereochemistry to natural ABA at the junction of the ring and side chain. In contrast, PBI-51 showed no agonistic effects until applied at 40 to 50 micromolar. Even then, the response was fairly weak. PBI-51 has the opposite stereochemistry to natural ABA at the junction of the ring and side chain. When applied concurrently with ABA, PBI-63 and PBI-51 had distinctly different properties. PBI-63 (40 micromolar) and ABA (5 micromolar) combined gave results similar to the application of either compound separately with high levels of induction of napin expression. PBI-51 displayed a reversible antagonistic effect with ABA, shifting the typical ABA dose-response curve by a factor of 4 to 5. This antagonism was noted for the expression of two ABA-sensitive genes, napin and oleosin. To test whether this antagonism was at the level of ABA recognition or uptake, ABA uptake was monitored in the presence of PBI-51 or PBI-63. Neither compound decreased ABA uptake. Treatments with either PBI-51 or PBI-63 showed an effect on endogenous ABA pools by permitting increases of 5- to 7-fold. It is hypothesized that this increase occurs because of competition for ABA catabolic enzymes by both compounds. The fact that ABA pools did not decrease in the presence of PBI-51 suggests that PBI-51 m