The overexpression of RXam1, a cassava gene coding for an RLK, confers disease resistance to Xanthomonas axonopodis pv. manihotis

Abstract

The overexpression of RXam1 leads to a reduction in bacterial growth of XamCIO136, suggesting that RXam1 might be implicated in strain-specific resistance. Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) is a prevalent disease in all regions, where cassava is cultivated. CBB is a foliar and vascular disease usually controlled through host resistance. Previous studies have found QTLs explaining resistance to several Xam strains. Interestingly, one QTL called XM5 that explained 13% of resistance to XamCIO136 was associated with a similar fragment of the rice Xa21-resistance gene called PCR250. In this study, we aimed to further identify and characterize this fragment and its role in resistance to CBB. Screening and hybridization of a BAC library using the molecular marker PCR250 as a probe led to the identification of a receptor-like kinase similar to Xa21 and were called RXam1 (Resistance to Xam 1). Here, we report the functional characterization of susceptible cassava plants overexpressing RXam1. Our results indicated that the overexpression of RXam1 leads to a reduction in bacterial growth of XamCIO136. This suggests that RXAM1 might be implicated in strain-specific resistance to XamCIO136.

Innate Immunity Activation and RNAi Interplay in Citrus Exocortis Viroid—Tomato Pathosystem

“…Besides these MAP kinases, many groups of kinases showing homologies between each other and with known or supposed PRRs were also found to be upregulated in infected plants, including 53 lectin receptor-like kinases (45 G-type and 8 L-type), including 5 LECRK-like kinases involved in innate immunity [ 41 ], 23 LRK10-like homologous to a receptor-like protein kinase involved in wheat rust resistance [ 42 ], 12 RLKs homologous to Arabidopsis gene At3g47570 showing similarity to the gene RXam1 conferring resistance against a strain of Xanthomonas axonopodis pv. manihotis [ 43 ], three homologs of FLS2 known as the PRR that determines the specific perception of the bacterial flagellin flg22 [ 44 ], one EFR known as PRR interacting with the peptide elf18 (derived from bacterial EF-Tu) [ 45 ], and one homolog of Hcr9-4E providing resistance against Cladosporium fulvum [ 46 ]. Beside immunity-related kinases, 21 kinases showing homology with RLP12-like proteins involved in meristem maintenance were also upregulated in infected plants ( Table S9 ).…”

Cassava diseases caused byXanthomonas phaseolipv.manihotisandXanthomonas cassavae

“…RXam1 shows similarity to the anti‐ Xanthomonas oryzae pv. oryzae rice resistance gene Xa21 , and was recently shown to be involved in defence against Xpm strain CIO136 (Díaz‐Tatis et al, 2018 ). RXam2 is a typical non‐TIR NB‐LRR located in a QTL explaining 61% of the resistance variance to Xpm strain CIO151.…”

HpaXpm, a novel harpin of Xanthomonas phaseoli pv. manihotis, acts as an elicitor with high thermal stability, reduces disease, and promotes plant growth

“…To date, there have been no reports of harpins derived from cassava pathogens. Cassava (Manihot esculenta Crantz) is a particularly important cash crop [18,19] in the tropics, where it is considered a staple crop and one of the main sources of calories for more than one billion people [18,20]. The most important bacterial disease of cassava is cassava bacterial blight, which is caused by the Gram-negative bacterium Xanthomonas phaseoli pv.…”

“…The most important bacterial disease of cassava is cassava bacterial blight, which is caused by the Gram-negative bacterium Xanthomonas phaseoli pv. manihotis (Xpm) [18,20]. The characterization of new harpin members improves our understanding of the evolutionary relationships of harpins and provides more possibilities for understanding the mechanism of harpins that underlies the interaction between pathogens and plants.…”