Frameshift Mutation Confers Function as Virulence Factor to Leucine-Rich Repeat Protein from Acidovorax avenae

Abstract

Many plant pathogens inject type III (T3SS) effectors into host cells to suppress host immunity and promote successful infection. The bacterial pathogen Acidovorax avenae causes brown stripe symptom in many species of monocotyledonous plants; however, individual strains of each pathogen infect only one host species. T3SS-deleted mutants of A. avenae K1 (virulent to rice) or N1141 (virulent to finger millet) caused no symptom in each host plant, suggesting that T3SS effectors are involved in the symptom formation. To identify T3SS effectors as virulence factors, we performed whole-genome and predictive analyses. Although the nucleotide sequence of the novel leucine-rich repeat protein (Lrp) gene of N1141 had high sequence identity with K1 Lrp, the amino acid sequences of the encoded proteins were quite different due to a 1-bp insertion within the K1 Lrp gene. An Lrp-deleted K1 strain (KΔLrp) did not cause brown stripe symptom in rice (host plant for K1); by contrast, the analogous mutation in N1141 (NΔLrp) did not interfere with infection of finger millet. In addition, NΔLrp retained the ability to induce effector-triggered immunity (ETI), including hypersensitive response cell death and expression of ETI-related genes. These data indicated that K1 Lrp functions as a virulence factor in rice, whereas N1141 Lrp does not play a similar role in finger millet. Yeast two-hybrid screening revealed that K1 Lrp interacts with oryzain α, a pathogenesis-related protein of the cysteine protease family, whereas N1141 Lrp, which contains LRR domains, does not. This specific interaction between K1 Lrp and oryzain α was confirmed by Bimolecular fluorescence complementation assay in rice cells. Thus, K1 Lrp protein may have acquired its function as virulence factor in rice due to a frameshift mutation.

The Transcription Factor Lrp of Pantoea stewartii subsp. stewartii Controls Capsule Production, Motility, and Virulence Important for in planta Growth

“…Previously, Lrp has been demonstrated to play a role in the virulence of some plant pathogens, including Xanthomonas spp. ( Cubero and Graham, 2004 ), Acidovorax avenae ( Kondo et al, 2017 ) and Erwinia amylovora ( Schachterle and Sundin, 2019 ). Similarly, our findings indicate critical roles of Lrp for P. stewartii with regard to capsule production, motility, growth, and virulence.…”

Novel Effector RHIFs Identified From Acidovorax avenae Strains N1141 and K1 Play Different Roles in Host and Non-host Plants

“…Moreover, sequence analysis of regions flanking the transposons revealed that they were inserted into 68 different genes. In addition, multiple proteins were secreted by strains N1141 and K1 using their T3SS (Kondo et al, 2017;Kawaguchi et al, 2021). The presence of multiple effectors in A. avenae strains N1141 and K1 raises the question of whether NRHIF and KRHIF are the only ETI-inducible effectors for rice and finger millet, respectively.…”

“…Cultures of rice cells were grown at 30°C under light irradiation (Baba et al, 1986 week, and all experiments were performed 4 days after transfer. Acidovorax avenae N1141 (MAFF 301141), T3SS-deficient N1141 strain (NΔT3SS), K1 (MAFF 301755), and T3SS-deficient K1 strain (KΔT3SS) were used as previously described (Kadota et al, 1996;Che et al, 2000;Kondo et al, 2017). Rice (O. sativa L. subsp.…”

“…Inoculation of A. avenae to rice or finger millet was performed by previously described method (Kondo et al, 2017), with the slightly modifications. The bacteria suspended in sterilized distilled water (1 × 10 6 cfu/μl) were drop on the end of a needle in an amount of one microliter (10 6 cfu), and then the sheath of 3 weeks old seedlings was pricked at a point 3 cm above the soil level.…”