Download Title:Functional Study of the Peptide Hormone IbHypSys

Title:Functional Study of the Peptide Hormone IbHypSys
in Signal Transduction
Author：萬威麟 Wei-Lin Wan
M09
Advisor：Dr. Shih-Tong Jeng
5
Abstract
Plants have evolved defence mechanisms for survival against various kinds of
predators and pathogens. Plant peptide signals have recently been discovered to
induce defence genes for protection against both herbivores and pathogens. The
hydroxyproline-rich systemins (HypSys) are glycopeptides containing 18–20 amino
acids in length, and they are processed from larger precursors. HypSys induce the
production of jasmonate（JA） and function to amplify the defence response. Each
HypSys peptide contains a hydroxyprolinerich inner core that is the site of
glycosylation. The HypSys precursors contain a signal sequence, indicating that they
are secreted to the apoplast. The first nonsolanaceous HypSys peptide was isolated
from Ipomoea batatas cv. Georgia Jet, called IbHypSys. The precursor of IbHypSys
contained six putative signaling peptides and a signal sequence. IbpreproHypSys can
be induced by wound. IbpreproHypSys and sporamin were induced by IbHypSys
treatment. In this study, we found that IbHypSys also existed in Ipomoea batatas cv.
Tainung 57. It also showed that IbHypSys only expressed in leafs and roots. Several
downstream genes, including IbHypSys and IPO, can be induced by
synthetic IbHypSys IV treatment. IbHypSys IV treatment also induced H2O2
production in 0.5 hour and the expression of H2O2-relative genes, such as ascorbate
peroxidase（APX）and superoxide dismutase（SOD）, indicating that H2O2 was
involved in signal transduction caused by IbHypSys. The expression of IbHypSys
after IbHypSys IV treatment was inhibited by the presence of 1mM ethylene glycol
tetraacetic acid (EGTA) or 10 mM Diethyldithiocarbamic aid （DIECA）, and this
meant that Ca2+ and JA were factors for IbHypSys signal transduction. Furthermore,
overexpression of IbpreproHypSys in sweet potato led to higher basal level of H2O2
and the greater expression of PR1-like gene after wounding than wild-type plant did.
These results might point out that IbHypSys regulated reactive oxygen species, which
further control plant defence system.