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A Diketopiperazine, Cyclo-(L-Pro-L-Ile), Derived From Bacillus thuringiensis JCK-1233 Controls Pine Wilt Disease by Elicitation of Moderate Hypersensitive Reaction
Ist Teil von
Frontiers in plant science, 2020-07, Vol.11, p.1023-1023
Ort / Verlag
Frontiers Media S.A
Erscheinungsjahr
2020
Link zum Volltext
Quelle
EZB Free E-Journals
Beschreibungen/Notizen
Pine wilt disease (PWD) caused by the pine wood nematode (PWN)
Bursaphelenchus xylophilus
is one of the devastating diseases affecting pine forests worldwide. Although effective control measurements are still missing, induction of resistance could represent a possible eco-friendly alternative. In this study, induced resistance-based
in vitro
and
in vivo
screening tests were carried out for selection of bacteria with the ability to suppress PWD. Out of 504 isolated bacteria,
Bacillus thuringiensis
JCK-1233 was selected for its ability to boost pathogenesis-related 1 (
PR1
) gene expression, a marker of systemic acquired resistance. Moreover, treatment of pine seedlings with
B. thuringiensis
JCK-1233 resulted in increased expression of other defense-related genes, and significantly inhibited PWD development under greenhouse conditions. However,
B. thuringiensis
JCK-1233 showed no direct nematicidal activity against
B. xylophilus
. To identify the effective compound responsible for the induction of resistance in
B. thuringiensis
JCK-1233, several diketopiperazines (DPKs) including
cyclo
-(D-Pro-L-Val),
cyclo
-(L-Pro-L-Ile),
cyclo
-(L-Pro-L-Phe), and
cyclo
-(L-Leu-L-Val) were isolated and tested. Foliar treatment of pine seedlings with
Cyclo
-(L-Pro-L-Ile) resulted in suppression of PWD severity and increased the expression of defense-related genes similarly to
B. thuringiensis
JCK-1233 treatment. Interestingly, treatment with
B. thuringiensis
JCK-1233 or
cyclo
-(L-Pro-L-Ile) showed moderately enhanced expression of
PR-1
,
PR-2
,
PR-3
,
PR-4
,
PR-5
, and
PR-9
genes following inoculation with PWN compared to that in the untreated control, indicating that they mitigated the burst of hypersensitive reaction in susceptible pine seedlings. In contrast, they significantly increased the expression levels of
PR-6
and
PR-10
before PWN inoculation. In conclusion, foliar spraying with either
B. thuringiensis
JCK-1233 culture suspension or DPKs could induce resistance in pine seedlings, thereby alleviating the serious damage by PWD. Taken together, this study supports aerial spraying with eco-friendly biotic or abiotic agents as a valuable strategy that may mark an epoch for the control of PWD in pine forests.