Salicylic acid inhibits gibberellin-induced alpha-amylase expression and seed germination via a pathway involving an abscisic-acid-inducible WRKY gene

Plant Mol Biol. 2007 Jun;64(3):293-303. doi: 10.1007/s11103-007-9152-0. Epub 2007 Mar 28.

Abstract

It is well known that abscisic acid (ABA) antagonizes gibberellin (GA)-promoted seed germination. Recent circumstantial evidence suggests that salicylic acid (SA) also inhibits seed germination in maize and Arabidopsis. Our study shows that SA blocks barley seed germination in a dosage dependent manner. As an initial effort to addressing the mechanism controlling the crosstalk of SA, GA and ABA signaling in barley, we studied the regulation of alpha-amylases by SA and a WRKY gene whose expression is modulated by these hormones. Assays of alpha-amylase activity reveal that GA-induced alpha-amylase production in aleurone cells is inhibited by bioactive SA, but not its analogs, 3-hydroxybenzoic acid and 4-hydroxybenzoic acid. This inhibitory effect is unlikely due to repressing alpha-amylase secretion or inhibiting alpha-amylase enzyme activities. Northern blot analyses indicate that SA suppresses GA-induced expression of a barley low pI alpha-amylase gene (Amy32b). Because our previous data indicate that ABA-inducible and GA-suppressible WRKY genes inhibit the expression of alpha-amylase genes in rice, we studied the steady state mRNA levels of a barley WRKY gene, HvWRKY38. The expression of HvWRKY38 in barley aleurone cells is down-regulated by GA, but up-regulated by SA and ABA. However, the regulation of HvWRKY38 by SA appears to be different from that of ABA in term of the kinetics and levels of induction. Over-expression of HvWRKY38 in aleurone cells by particle bombardment blocks GA induction of the Amy32b promoter reporter construct (Amy32b-GUS). Therefore, HvWRKY38 might serve as a converging node of SA and ABA signal pathways involved in suppressing GA-induced seed germination.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Gene Expression Regulation, Plant / drug effects
  • Germination / drug effects*
  • Gibberellins / antagonists & inhibitors
  • Gibberellins / pharmacology*
  • Hordeum / embryology
  • Hordeum / enzymology
  • Hordeum / genetics*
  • Plant Proteins / biosynthesis
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Repressor Proteins / biosynthesis
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Salicylic Acid / pharmacology*
  • Seeds / growth & development
  • Signal Transduction
  • alpha-Amylases / biosynthesis*
  • alpha-Amylases / genetics

Substances

  • Gibberellins
  • Plant Proteins
  • Repressor Proteins
  • alpha-Amylases
  • Salicylic Acid