Preliminary Identification On Antipathogenic Function Of Gene MtPiI4 From Medicago Truncatula

Proteinase inhibitors (PIs), a family of protein or peptides widely existing in animials and plants, play important roles in response to environmental stimuli. The functions of PI mainly consist of two aspects:1. to prevent uncontrolled proteolysis within cells to guarantee the normal function of these limited proteolysis; and 2. to protect proteins from foreign proteolytic enzymes, which, accordingly, are insects resistance and protease activities regulation macroscopically. However, the role of PIs in regulating plant immune responses against bacterial infection rather than directly interacting with pathogens is rarely understood. In this study, a novel gene MtPiI4 encoding a serpin (proteinase inhibitor 14) with a conserved DUF716 domain was isolated and functionally characterized from Medicago truncatula. MtPiI4 was differentially expressed in different issues and organs. It was highly expressed in leaves, stems, and roots, while was weakly expressed in seeds and flowers.The expression of MtPiI4 could be up-regulated by inoculation with a typical bacterial pathogen P. syringae pv. tomato DC3000 strain (Pst DC3000). It could also be induced by exogenous methyl jasmonate (MeJA) treatment and mechanical wounding, separately, but down-regulated by exogenous Salicylic acid (SA) in leaves. These results were consistent with characters of most PIs.To further identify its function in regulating plant immunity against Pst DC3000, we constructed the transgenic Arabidopsis plants overexpressing MtPiI4, named 35S::MtPiI4. Compared to the wild type Arabidopsis,35S::MtPiI4 lines showed decreased sensitivity to MeJA and enhanced resistance to Pst DC3000. The 35S::MtPiI4 Arabidopsis displayed repressed JA singling in response to Pst DC3000, which could be indicated by the decreased expression of JA-related genes (LOX2, PDF 1.2, and VSP1) in 35S::MtPiI4 as compared to the wild type. The overexpression of MtPiI4 in Arabidopsis resulted in the up-regulation of NPR1 (a negative regulator of JA signaling) and down-regulation of MAPK4 (a positive regulator of JA signaling). MtPiI4 can manipulate a feedback regulation to upstream genes and give way to SA singaling genes through hijacking JA singaling genes. All of these results provided novel evidence indicating that MtPiI4 helped plant against Pst DC3000 infection by suppressing JA signaling pathway.