Abstract
Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) seriously affects cassava yield. Genes encoding nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains are among the most important disease resistance genes in plants that are specifically involved in the response to diverse pathogens. However, the in vivo roles of NBS-LRR remain unclear in cassava (Manihot esculenta). In this study, we isolated four MeLRR genes and assessed their expression under salicylic acid (SA) treatment and Xam inoculation. Four MeLRR genes positively regulate cassava disease general resistance against Xam via virus-induced gene silencing (VIGS) and transient overexpression. During cassava-Xam interaction, MeLRRs positively regulated endogenous SA and reactive oxygen species (ROS) accumulation and pathogenesis-related gene 1 (PR1) transcripts. Additionally, we revealed that MeLRRs positively regulated disease resistance in Arabidopsis. These pathogenic microorganisms include Pseudomonas syringae pv. tomato, Alternaria brassicicola, and Botrytis cinerea. Our findings shed light on the molecular mechanism underlying the regulation of cassava resistance against Xam inoculation.
Highlights
Disease resistance genes (R genes) usually act as receptors of pathogen-encoded effector proteins, which are often secreted by pathogens directly into host cells (Urbach and Ausubel, 2017)
MeLRR1, MeLRR3, and MeLRR4 belong to CC-nucleotide-binding site (NBS)-leucine-rich repeat (LRR) protein, while MeLRR2 is one of the Toll/interleukin-1 receptor-like (TIR)-NBS-LRR protein
Bioinformatics predicted that the MeLRR proteins were unstable and hydrophilic (Supplementary Table 1)
Summary
Disease resistance genes (R genes) usually act as receptors of pathogen-encoded effector proteins, which are often secreted by pathogens directly into host cells (Urbach and Ausubel, 2017). In the past few years, NBS-LRR genes in several plant species have been isolated via genome-wide analysis, including mango (Mangifera indica) (Lei et al, 2014), cassava (Manihot esculenta) (Lozano et al, 2015; Utsumi et al, 2016), sorghum (Sorghum bicolor) (Yang and Wang, 2016), wheat (Triticum aestivum) (Li et al, 2017), cotton (Gossypium hirsutum) (Deng et al, 2019), maize (Zea mays) (Xu et al, 2018), soybean (Glycine max) (Zhao et al, 2018), grapevine (Vitis vinifera) (Goyal et al, 2020), and yam (Dioscorea rotundata) (Zhang et al, 2020). The expression levels of four chosen MeLRRs were significantly induced by exogenous application of SA treatment and Xam inoculation These genes positively regulated cassava resistance to Xam inoculation. The functional analysis of MeLRR genes will offer potential roles in genetic breeding for disease-resistant cassava
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