Abstract
BackgroundMatrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases. MMPs have been characterized in detail in mammals and shown to play key roles in many physiological and pathological processes. Although MMPs in some plant species have been identified, the function of MMPs in biotic stress responses remains elusive.ResultsA total of five MMP genes were identified in tomato genome. qRT-PCR analysis revealed that expression of Sl-MMP genes was induced with distinct patterns by infection of Botrytis cinerea and Pseudomonas syringae pv. tomato (Pst) DC3000 and by treatment with defense-related hormones such as salicylic acid, jasmonic acid and ethylene precursor 1-amino cyclopropane-1-carboxylic acid. Virus-induced gene silencing (VIGS)-based knockdown of individual Sl-MMPs and disease assays indicated that silencing of Sl3-MMP resulted in reduced resistance to B. cinerea and Pst DC3000, whereas silencing of other four Sl-MMPs did not affect the disease resistance against these two pathogens. The Sl3-MMP-silenced tomato plants responded with increased accumulation of reactive oxygen species and alerted expression of defense genes after infection of B. cinerea. Transient expression of Sl3-MMP in leaves of Nicotiana benthamiana led to an enhanced resistance to B. cinerea and upregulated expression of defense-related genes. Biochemical assays revealed that the recombinant mature Sl3-MMP protein had proteolytic activities in vitro with distinct preferences for specificity of cleavage sites. The Sl3-MMP protein was targeted onto the plasma membrane of plant cells when transiently expressed in onion epidermal cells.ConclusionVIGS-based knockdown of Sl3-MMP expression in tomato and gain-of-function transient expression of Sl3-MMP in N. benthamiana demonstrate that Sl3-MMP functions as a positive regulator of defense response against B. cinerea and Pst DC3000.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0536-z) contains supplementary material, which is available to authorized users.
Highlights
Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases
Identification of the Sl-MMP family in tomato To identify members of the MMP family in tomato, HMM and Blastp searches using MMP proteins previously reported from Arabidopsis and other plant species as queries against the recently published tomato genome sequences (Release Version ITAG2.40) were performed
All five Sl-MMPs are intronless genes, which is consistent with structural features of genes for MMPs in Arabidopsis, soybean, cucumber and Medicago truncatula [13, 15, 17, 19, 21]
Summary
MMPs have been characterized in detail in mammals and shown to play key roles in many physiological and pathological processes. The MMP family is characterized by the presence of a highly conserved catalytic domain containing an HEXXHXXGXX(H/D) zincbinding sequence followed by a conserved methionine that forms a tight 1,4-β turn called Met-turn [4]. Members of this family have mainly been studied in mammals, but have been found in simpler animals and plants [5]. It has been shown that human MMPs play key roles in many physiological and pathological processes [9, 10]
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