Wheat Apoplast-Localized Lipid Transfer Protein TaLTP3 Enhances Defense Responses Against Puccinia triticina

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 <i>Triticum aestivum</i> lipid transfer protein 3 (<i>TaLTP3</i>) gene was unregulated during incompatible interaction mediated by leaf rust resistance genes <i>Lr39/41</i> at the early infection stage. Stable transgenic wheat lines overexpressing <i>TaLTP3</i> exhibited enhanced resistance to leaf rust pathogen <i>Puccinia triticina</i>. Transcriptome analysis revealed that overexpression of <i>TaLTP3</i> 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 <i>Pseudomonas syringae</i> pv. <i>tomato</i> DC3000. Further investigation indicated that <i>TaLTP3</i> physically associated with wheat <i>TaPR1a</i> protein in the apoplast. Transgenic wheat lines overexpressing <i>TaLTP3</i> and <i>TaPR1a</i> showed higher accumulations of reactive oxygen species (ROS) during plant defense responses. All these findings suggested that <i>TaLTP3</i> is involved in wheat resistance against leaf rust pathogen infection and forming a <i>TaLTP3-TaPR1a</i> complex in apoplast against this pathogen, which provides new insights into the functional roles of PR proteins.