Phytotoxin synthesis genes and type III effector genes of Pseudomonas syringae pv. actinidiae biovar 6 are regulated by culture conditions.

Karin Hirose,Yasuhiro Ishiga,Takashi Fujikawa

doi:10.7717/peerj.9697

Abstract

The kiwifruit bacterial canker (Pseudomonas syringae pv. actinidiae; Psa) causes severe damage to kiwifruit production worldwide. Psa biovar 6 (Psa6), which was isolated in Japan in 2015, produces two types of phytotoxins: coronatine and phaseolotoxin. To elucidate the unique virulence of Psa6, we performed transcriptomic analysis of phytotoxin synthesis genes and type III effector genes in in vitro cultivation using various media. The genes related to phytotoxin synthesis and effectors of Psa6 were strictly regulated in the coronatine-inducing mediums (HS and HSC); 14 of 23 effector genes and a hrpL sigma factor gene were induced at 3 h after transferring to the media (early-inducible genes), and phytotoxin synthesis genes such as argD of phaseolotoxin and cfl of coronatine were induced at 6 and 12 h after transferring to the media (late-inducible genes). In contrast, induction of these genes was not observed in the hrp-inducing medium. Next, to examine whether the changes in gene expression in different media is specific to Psa6, we investigated gene expression in other related bacteria. For Psa biovar 1 (Psa1), biovar 3 (Psa3), and P. s. pv. glycinea (Psg), no clear trends were observed in expression behavior across various culture media and incubation times. Therefore, Psa6 seems to exert its virulence efficiently by using two phytotoxins and effectors according to environmental changes. This is not seen in other biovars and pathovars, so it is thought that Psa6 has acquired its own balance of virulence.

Highlights

Kiwifruit belong to the family Actinidiaceae and the genus Actinidia
RNA-Seq of Psa biovar 6 (Psa6) revealed the behavior of 5,796 genes (Table S2).The expression values from the HS medium at 27 oC were used to calculate the expression values from the HS medium at 18
To clarify the role of temporal changes in the behavior of virulence genes, such as type III effector genes and phytotoxin synthesis genes, we examined the behavior of gene expression over time using reverse transcription-quantitative PCR (RT-qPCR) analysis

Summary

Introduction

Kiwifruit belong to the family Actinidiaceae and the genus Actinidia. They include Actinidia deliciosa, a species whose flesh is green, and A. chinensis, a species whose flesh is yellow or red.In Japan, kiwifruit seedlings were first introduced from New Zealand in the 1970s and are popular as edible fruit (Ushiyama, 1993). Kiwifruit belong to the family Actinidiaceae and the genus Actinidia. They include Actinidia deliciosa, a species whose flesh is green, and A. chinensis, a species whose flesh is yellow or red. In Japan, kiwifruit seedlings were first introduced from New Zealand in the 1970s and are popular as edible fruit (Ushiyama, 1993). Around 1980, kiwifruit bacterial canker broke out and caused serious damage to kiwifruit production (Takikawa et al, 1989). Since this disease has resulted in economic and productive damage in kiwifruit orchards throughout Japan. The pathogen that causes kiwifruit bacterial canker is Pseudomonas syringae pv

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Conclusion