Defensin-like peptides in wheat analyzed by whole-transcriptome sequencing: a focus on structural diversity and role in induced resistance

Abstract

Antimicrobial peptides (AMPs) are the main components of the plant innate immune system. Defensins represent the most important AMP family involved in defense and non-defense functions. In this work, global RNA sequencing and de novo transcriptome assembly were performed to explore the diversity of defensin-like (DEFL) genes in the wheat Triticum kiharae and to study their role in induced resistance (IR) mediated by the elicitor metabolites of a non-pathogenic strain FS-94 of Fusarium sambucinum. Using a combination of two pipelines for DEFL mining in transcriptome data sets, as many as 143 DEFL genes were identified in T. kiharae, the vast majority of them represent novel genes. According to the number of cysteine residues and the cysteine motif, wheat DEFLs were classified into ten groups. Classical defensins with a characteristic 8-Cys motif assigned to group 1 DEFLs represent the most abundant group comprising 52 family members. DEFLs with a characteristic 4-Cys motif CX{3,5}CX{8,17}CX{4,6}C named group 4 DEFLs previously found only in legumes were discovered in wheat. Within DEFL groups, subgroups of similar sequences originated by duplication events were isolated. Variation among DEFLs within subgroups is due to amino acid substitutions and insertions/deletions of amino acid sequences. To identify IR-related DEFL genes, transcriptional changes in DEFL gene expression during elicitor-mediated IR were monitored. Transcriptional diversity of DEFL genes in wheat seedlings in response to the fungus Fusarium oxysporum, FS-94 elicitors, and the combination of both (elicitors + fungus) was demonstrated, with specific sets of up- and down-regulated DEFL genes. DEFL expression profiling allowed us to gain insight into the mode of action of the elicitors from F. sambucinum. We discovered that the elicitors up-regulated a set of 24 DEFL genes. After challenge inoculation with F. oxysporum, another set of 22 DEFLs showed enhanced expression in IR-displaying seedlings. These DEFLs, in concert with other defense molecules, are suggested to determine enhanced resistance of elicitor-pretreated wheat seedlings. In addition to providing a better understanding of the mode of action of the elicitors from FS-94 in controlling diseases, up-regulated IR-specific DEFL genes represent novel candidates for genetic transformation of plants and development of pathogen-resistant crops.

Transcriptional analyses of differential cultivars during resistant and susceptible interactions with Peronospora effusa, the causal agent of spinach downy mildew

“…Spinach homologs of those genes encoding plant defensin-like proteins were also strongly expressed during the incompatible interaction, indicating their involvement in defense in this interaction. A number of studies have shown the inhibitory effect of plant defensin peptides to various fungal and bacterial pathogens [69][70][71][72] . Genes encoding ACC oxidase homologs in spinach were up-regulated across the infection times in our experiments.…”

A methyl jasmonate induced defensin like protein from Panax notoginseng confers resistance against Fusarium solani in transgenic tobacco

“…Plant defensins are induced as a part of the systemic defense response during pathogenic attack and environmental stresses, and defensin genes respond to some signalling molecules, including MeJA, ETH, and SA. After inoculation with F. oxysporum, many DEFLs show enhanced expressions in induced resistancedisplaying wheat seedlings (Odintsova et al 2019). The OsDEF expressions are highly induced by Aspergillus oryzae infection (Weerawanich et al 2018).…”

“…A total of 13 defensin genes have been identified in the Arabidopsis thaliana genome (Thomma et al 2002), and also 317 DEFLs (Silverstein et al 2005). In total, 93, 79, and 143 DEFL genes have been characterized in rice (Oryza sativa), grapevine (Vitis vinifera), and wheat (Triticum kiharae), respectively (Silverstein et al 2007, Giacomelli et al 2012, Odintsova et al 2019. In addition, the DEFLs have the hallmarks of defensin genes, including the conserved cysteine residues, CSαβ motif or γ-core motif (Silverstein et al 2005, Giacomelli et al 2012.…”

Functions of pipecolic acid on induced resistance against Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000 in tomato plants

“…Increasing evidence indicates that there exists significant association between amino acid metabolism and plant resistance to pathogens (Frerigmann et al., 2016; Stuttmann et al, 2011). Amino acids are not only precursors for defensive antimicrobial compounds but also can directly affect plant resistance to specific pathogens (Odintsova et al, 2019; Stuttmann et al., 2011). Pipecolic acid (Pip), a lysine‐derived non‐protein amino acid, has important functions in both plants and animals (Vranova, Lojkova, Rejsek, & Formanek, 2013; Xu et al., 2018; Yuan et al., 2017).…”