Abstract
BackgroundThe SR/CAMTA proteins represent a small family of transcription activators that play important roles in plant responses to biotic and abiotic stresses. Seven SlSR/CAMTA genes were identified in tomato as tomato counterparts of SR/CAMTA; however, the involvement of SlSRs/CAMTAs in biotic and abiotic stress responses is not clear. In this study, we performed functional analysis of the SlSR/CAMTA family for their possible functions in defense response against pathogens and tolerance to drought stress.ResultsExpression of SlSRs was induced with distinct patterns by Botrytis cinerea and Pseudomonas syringae pv. tomato (Pst) DC3000. Virus-induced gene silencing (VIGS)-based knockdown of either SlSR1 or SlSR3L in tomato resulted in enhanced resistance to B. cinerea and Pst DC3000 and led to constitutive accumulation of H2O2, elevated expression of defense genes, marker genes for pathogen-associated molecular pattern-triggered immunity, and regulatory genes involved in the salicylic acid- and ethylene-mediated signaling pathways. Furthermore, the expression of SlSR1L and SlSR2L in detached leaves and whole plants was significantly induced by drought stress. Silencing of SlSR1L led to decreased drought stress tolerance, accelerated water loss in leaves, reduced root biomass and attenuated expression of drought stress responsive genes in tomato. The SlSR1 and SlSR3L proteins were localized in the nucleus of plant cells when transiently expressed in Nicotiana benthamiana and had transcriptional activation activity in yeast.ConclusionsVIGS-based functional analyses demonstrate that both SlSR1 and SlSR3L in the tomato SlSR/CAMTA family are negative regulators of defense response against B. cinerea and Pst DC3000 while SlSR1L is a positive regulator of drought stress tolerance in tomato.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0286-3) contains supplementary material, which is available to authorized users.
Highlights
The SR/CAMTA proteins represent a small family of transcription activators that play important roles in plant responses to biotic and abiotic stresses
Expression patterns of SlSRs in response to pathogen infection To explore the possible functions of SlSRs in defense response against pathogen infection, we analyzed the expression patterns of SlSR genes in tomato plants after infection with different pathogens, B. cinerea, a necrotrophic fungal pathogen causing grey mold disease, and Pst DC3000, a biotrophic bacterial pathogen causing bacterial leaf spot disease
In analysis of expression patterns of SlSRs in response to infection of B. cinerea, leaf samples collected from the whole plant inoculation assays were used and the expression pattern of SlLapA, a defense gene regulated by the JA/ET-mediated signaling pathway [31], was monitored to confirm the efficiency of the inoculation procedure
Summary
The SR/CAMTA proteins represent a small family of transcription activators that play important roles in plant responses to biotic and abiotic stresses. Cellular Ca2+ changes can be sensed and interpreted by calcium-binding proteins (CaBPs) including calmodulin (CaM), calcineurin B-like proteins and calcium-dependent protein kinases [8,9,10]. These CaBPs regulate cellular responses through two distinct pathways upon sensing different biotic and abiotic signals [8,9,10]. CaBPs modulate indirect and relatively slow cellular responses by interacting with transcription factors to regulate gene expression. Biochemical studies with the Arabidopsis AtSR1 and rice OsCBT proteins have identified the primary target of DNA ciselement for SR/CAMTA proteins as CGCG and CGTG motifs in promoter regions of the target genes [12,14]
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