Abstract
The protein elicitor MoHrip2, which was extracted from Magnaporthe oryzae as an exocrine protein, triggers the tobacco immune system and enhances blast resistance in rice. However, the detailed mechanisms by which MoHrip2 acts as an elicitor remain unclear. Here, we investigated the structure of MoHrip2 to elucidate its functions based on molecular structure. The three-dimensional structure of MoHrip2 was obtained. Overall, the crystal structure formed a β-barrel structure and showed high similarity to the pathogenesis-related (PR) thaumatin superfamily protein thaumatin-like xylanase inhibitor (TL-XI). To investigate the functional regions responsible for MoHrip2 elicitor activities, the full length and eight truncated proteins were expressed in Escherichia coli and were evaluated for elicitor activity in tobacco. Biological function analysis showed that MoHrip2 triggered the defense system against Botrytis cinerea in tobacco. Moreover, only MoHrip2M14 and other fragments containing the 14 amino acids residues in the middle region of the protein showed the elicitor activity of inducing a hypersensitive response and resistance related pathways, which were similar to that of full-length MoHrip2. These results revealed that the central 14 amino acid residues were essential for anti-pathogenic activity.
Highlights
Plants survive under adverse circumstances including various of biotic factors because of a very effective immune system (Bernoux et al, 2011)
The gene actin was used as the internal control gene. These results indicated that MoHrip2 significantly enhanced N. benthamiana resistance against the fungal pathogen B. cinerea and that the 14 amino acid residues have a crucial role in the induced resistance to pathogens. These results show that the functional region of MoHrip2 responsible for HR induction and disease resistance are in the same short region that contains the 14 crucial amino acid residues
The MoHrip2 protein is a novel elicitor that was purified in our lab (NCBI locus XP_003709559) from M. oryzae 70-15; there is little known about the functional regions of this protein
Summary
Plants survive under adverse circumstances including various of biotic factors because of a very effective immune system (Bernoux et al, 2011). The plant immune system is complex and consists mostly of two major branches of defense (Jones and Dangl, 2006; Mishra et al, 2012; Hou et al, 2013). One branch involves plant cell surface-located pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and is named PAMP-triggered immunity (PTI). Another branch involves intracellular plant NLRs [nucleotidebinding, leucine-rich repeat (LRR) receptors] that recognize pathogen-secreted effectors and is called effector-triggered immunity (ETI). The plant immune system is based on the effective detection and recognition of different inducers from
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