Regulation of Arabidopsis defense responses against Spodoptera littoralis by CPK-mediated calcium signaling.
BACKGROUND
Plant Ca2+ signals are involved in a wide array of intracellular signaling pathways after pest invasion. Ca2+-binding sensory proteins such as Ca2+-dependent protein kinases (CPKs) have been predicted to mediate the signaling following Ca2+ influx after insect herbivory. However, until now this prediction was not testable.


RESULTS
To investigate the roles CPKs play in a herbivore response-signaling pathway, we screened the characteristics of Arabidopsis CPK mutants damaged by a feeding generalist herbivore, Spodoptera littoralis. Following insect attack, the cpk3 and cpk13 mutants showed lower transcript levels of plant defensin gene PDF1.2 compared to wild-type plants. The CPK cascade was not directly linked to the herbivory-induced signaling pathways that were mediated by defense-related phytohormones such as jasmonic acid and ethylene. CPK3 was also suggested to be involved in a negative feedback regulation of the cytosolic Ca2+ levels after herbivory and wounding damage. In vitro kinase assays of CPK3 protein with a suite of substrates demonstrated that the protein phosphorylates transcription factors (including ERF1, HsfB2a and CZF1/ZFAR1) in the presence of Ca2+. CPK13 strongly phosphorylated only HsfB2a, irrespective of the presence of Ca2+. Furthermore, in vivo agroinfiltration assays showed that CPK3-or CPK13-derived phosphorylation of a heat shock factor (HsfB2a) promotes PDF1.2 transcriptional activation in the defense response.


CONCLUSIONS
These results reveal the involvement of two Arabidopsis CPKs (CPK3 and CPK13) in the herbivory-induced signaling network via HsfB2a-mediated regulation of the defense-related transcriptional machinery. This cascade is not involved in the phytohormone-related signaling pathways, but rather directly impacts transcription factors for defense responses.
Kanchiswamy
Chidananda Nagamangala
CN
Global COE Program: Evolution and Biodiversity, Graduate School of Science, Kyoto University, Kyoto, Japan.
Takahashi
Hirotaka
H
Quadro
Stefano
S
Maffei
Massimo E
ME
Bossi
Simone
S
Bertea
Cinzia
C
Zebelo
Simon Atsbaha
SA
Muroi
Atsushi
A
Ishihama
Nobuaki
N
Yoshioka
Hirofumi
H
Boland
Wilhelm
W
Takabayashi
Junji
J
Endo
Yaeta
Y
Sawasaki
Tatsuya
T
Arimura
Gen-ichiro
G
D000818:Animals; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D003517:Cyclopentanes / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D009154:Mutation; D054883:Oxylipins / Q000378:metabolism; D010766:Phosphorylation; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D005030:Ethylenes; D054883:Oxylipins; D018749:RNA, Plant; D011994:Recombinant Proteins; D014157:Transcription Factors; C011006:jasmonic acid; C036216:ethylene; C516786:CPK3 protein, Arabidopsis; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium