Salicylic acid inhibits gibberellin-induced alpha-amylase expression and seed germination via a pathway involving an abscisic-acid-inducible WRKY gene.
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.
Xie
Zhen
Z
Department of Biological Sciences, University of Nevada, M/S 4004, 4505 Maryland Parkway, Las Vegas, NV 89154, USA.
Zhang
Zhong-Lin
ZL
Hanzlik
Shane
S
Cook
Everett
E
Shen
Qingxi J
QJ
D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000187:drug effects*; D005875:Gibberellins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D001467:Hordeum / Q000196:embryology / Q000201:enzymology / Q000235:genetics*; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D020156:Salicylic Acid / Q000494:pharmacology*; D012639:Seeds / Q000254:growth & development; D015398:Signal Transduction; D000516:alpha-Amylases / Q000096:biosynthesis* / Q000235:genetics
D005875:Gibberellins; D010940:Plant Proteins; D012097:Repressor Proteins; D000516:alpha-Amylases; D020156:Salicylic Acid