Genome Analysis of the Broad Host Range Necrotroph Nalanthamala psidii Highlights Genes Associated With Virulence.

Anita A Severn-Ellis,David Edwards,D Jasper G Rees,Jacqueline Batley,James K Hane,Maritha H Schoeman,Philipp E Bayer

doi:10.3389/fpls.2022.811152

Abstract

Guava wilt disease is caused by the fungus Nalanthamala psidii. The wilt disease results in large-scale destruction of orchards in South Africa, Taiwan, and several Southeast Asian countries. De novo assembly, annotation, and in-depth analysis of the N. psidii genome were carried out to facilitate the identification of characteristics associated with pathogenicity and pathogen evolution. The predicted secretome revealed a range of CAZymes, proteases, lipases and peroxidases associated with plant cell wall degradation, nutrient acquisition, and disease development. Further analysis of the N. psidii carbohydrate-active enzyme profile exposed the broad-spectrum necrotrophic lifestyle of the pathogen, which was corroborated by the identification of putative effectors and secondary metabolites with the potential to induce tissue necrosis and cell surface-dependent immune responses. Putative regulatory proteins including transcription factors and kinases were identified in addition to transporters potentially involved in the secretion of secondary metabolites. Transporters identified included important ABC and MFS transporters involved in the efflux of fungicides. Analysis of the repetitive landscape and the detection of mechanisms linked to reproduction such as het and mating genes rendered insights into the biological complexity and evolutionary potential of N. psidii as guava pathogen. Hence, the assembly and annotation of the N. psidii genome provided a valuable platform to explore the pathogenic potential and necrotrophic lifestyle of the guava wilt pathogen.

Highlights

Guava (Psidium guajava L.), a tropical fruit crop belonging to the family Myrtaceae (Nakasone and Paull, 1998) gained commercial significance due to its versatility and nutritional value
Repetitive elements were found dispersed across all scaffolds covering an estimated 4.94% (2,662,768 bp) of the genome and comprising of 3,630 interspersed repeats (3.59%) as well as 12,602 simple repeats (447,835 bp) (1.18%)
Genomics has afforded us a unique glimpse into the N. psidii genome and potential mechanisms associated with virulence and adaptation

Summary

Introduction

Guava (Psidium guajava L.), a tropical fruit crop belonging to the family Myrtaceae (Nakasone and Paull, 1998) gained commercial significance due to its versatility and nutritional value. Guava wilt disease (GWD), caused by Nalanthamala psidii, was first reported in Taiwan in 1923 (Kurosowa, 1926). Severe losses in production were reported in Bangladesh as a result of guava wilt disease (Alam et al, 2019). With leaves initially turning yellow and changing over time to red and brown. Eventually resulting in the complete defoliation of the tree (Schoeman et al, 1997). A rapid sectorial decline of the tree is observed whereby leaves on affected branches wilt and die, and fruit development ceases. Development of gray to reddishbrown blisters on the trunks and branches follows from which white to salmon colored conidial masses and sporodochia are subsequently released (Schoeman et al, 1997).

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