Genetic Diversity in FUB Genes of Fusarium oxysporum f. sp. cubense Suggests Horizontal Gene Transfer.

Siwen Liu,Zongzhuan Shen,Xiuwu Guo,Shuxia Lv,Bo Wu,Ganjun Yi,Chunyu Li,Rong Li

doi:10.3389/fpls.2019.01069

Abstract

Fusaric acid (FA) is an important secondary metabolite of many Fusarium species and involved in the wilt symptoms caused in banana by Fusarium oxysporum f. sp. cubense (Foc). To investigate the evolution characteristics of the 12 Foc FA biosynthetic genes (FUB), coding sequences of the 12 FUB genes and three housekeeping genes, EF-1α/RPB1/RPB2 (translation elongation factor-1α/RNA polymerase II subunit I/RNA polymerase II subunit II), were subjected to genetic diversity analysis, phylogenetic analysis, recombination detection, and selective pressure analysis. The results of selective pressure analysis showed that the 15 genes were mainly subjected to negative selection. However, a significantly higher number of silent mutations, which could not be simply explained by selective pressure difference, were observed in the 12 FUB genes in Foc than in the three housekeeping genes. Infraspecies phylogeny and recombination detection analysis showed that significantly more horizontal gene transfer (HGT) events (normalized) had occurred in the FUB genes than in the three housekeeping genes. In addition, many of these events involved outgroup isolates and significantly increased the genetic diversity of FUB genes in Foc. The infraspecies phylogenetic analysis suggested that the polyphyletic phylogeny proposed for Foc requires further discussion, and the divergence of race 1, race 4, and the common ancestor of several F. oxysporum (Fo) isolates pathogenic to nonbanana plants should have diverged over a short period. Finally, our results suggest that the FUB genes in Fo should have benefited from HGT to gain a relatively high genetic diversity to respond to different host plants and environments despite mainly being subject to negative selection.

Highlights

Fusarium oxysporum (Fo) f. sp. cubense (Foc), the causal agent of Fusarium wilt of banana (Musa spp.), which is known as Panama disease, is the most important soil-borne pathogen limiting banana production in the world (Ploetz, 2015)
coding sequences (CDSs) of three housekeeping genes (EF-1α, RPB1, and RPB2) and 12 FUB genes with a total length of 33,168 bp were subtracted from the assembled genome sequences of 16 race 1 group (R1) isolates and 18 race 4 group (R4) isolates (Table 1)
In this study, we demonstrated that the genetic diversity and phylogeny of Foc isolates did have some specific characteristics in the 12 FUB genes compared with the housekeeping genes

Summary

Introduction

Fusarium oxysporum (Fo) f. sp. cubense (Foc), the causal agent of Fusarium wilt of banana (Musa spp.), which is known as Panama disease, is the most important soil-borne pathogen limiting banana production in the world (Ploetz, 2015). FA is involved in the toxicity of Fusarium spp. towards plants, animals, and human beings (Ghazi et al, 2017; Singh et al, 2017; López-Díaz et al, 2018) and in interactions with environmental microorganisms (Brown et al, 2015; Bohni et al, 2016; Simonetti et al, 2018). In Panama disease, FA production by Foc is involved in disturbing the water balance and causing the wilt symptom (Dong et al, 2012; Li et al, 2013; Dong et al, 2014) and has been shown to be essential for its virulence on banana plantlets (Ding et al, 2018)

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