Abstract
Plant apoplast serves as the frontier battlefield of plant defense in response to different types of pathogens. Many pathogenesis-related (PR) proteins are accumulated in apoplastic space during the onset of plant–pathogen interaction, where they act to suppress pathogen infection. In this study, we found the expression of Triticum aestivum lipid transfer protein 3 (TaLTP3) gene was unregulated during incompatible interaction mediated by leaf rust resistance genes Lr39/41 at the early infection stage. Stable transgenic wheat lines overexpressing TaLTP3 exhibited enhanced resistance to leaf rust pathogen Puccinia triticina. Transcriptome analysis revealed that overexpression of TaLTP3 specifically activated the transcription of pathogenesis-related protein 1a (TaPR1a) and multiple plant hormone pathways, including salicylic acid (SA), jasmonic acid (JA), and auxin, in response to the infection of the model bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Further investigation indicated that TaLTP3 physically associated with wheat TaPR1a protein in the apoplast. Transgenic wheat lines overexpressing TaLTP3 and TaPR1a showed higher accumulations of reactive oxygen species (ROS) during plant defense responses. All these findings suggested that TaLTP3 is involved in wheat resistance against leaf rust pathogen infection and forming a TaLTP3-TaPR1a complex in apoplast against this pathogen, which provides new insights into the functional roles of PR proteins.
Highlights
Plants utilize complex defense mechanisms to fight against pathogen infections
Apoplast represents the initial battlefield between plant and phytopathogens interaction and apoplastic immunity plays an important role in plant defense responses
Our studies showed that both the Triticum aestivum lipid transfer protein 3 (TaLTP3) and TaPR1a are secreted into the apoplastic space (Figure 4; Bi et al, 2020)
Summary
Plants utilize complex defense mechanisms to fight against pathogen infections. Apoplastic space represents an essential site for pathogen infection and the frontier battlefield of plant defense response, where either plant-secreted proteins, such as proteases and pathogenesis-related (PR) proteins, directly interact with pathogens or cell surfacelocalized pattern recognition receptors (PRRs) perceive pathogen-associated molecular patterns (PAMPs) to initiate PAMP-triggered immunity (PTI) (Jashni et al, 2015; Qi et al, 2017). PR protein-encoding genes are highly induced by pathogen infections, leading to the enrichment of PR proteins in the apoplast that participate in various plant defense responses (Van Loon et al, 2006; Wang et al, 2018). Overexpression of wheat homolog of PR1 gene (TaPR1a) in transgenic wheat line resulted in significantly enhanced resistance against both stripe rust and leaf rust fungi (Bi et al, 2020). They found that the model bacterial pathogen Pseudomonas syringae (P. syringae) pv. They found that the model bacterial pathogen Pseudomonas syringae (P. syringae) pv. tomato DC3000 was sufficient to activate the transcriptional response of TaPR1amediated plant defense
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