Ommochrome pathway genes kynurenine 3-hydroxylase and cardinal participate in eye pigmentation in Plutella xylostella

Xuejiao Xu,Tim Harvey-Samuel,Minsheng You,Jie Yang,Luke Alphey

doi:10.1186/s12860-020-00308-8

Abstract

BackgroundEye pigmentation genes have been utilized as visible markers for constructing genetic control prototypes in several insect vectors of human disease. Here, orthologs of two ommochrome pathway genes, kynurenine 3-hydroxylase (kmo) and cardinal, were investigated in Plutella xylostella, a globally distributed, economically important pest of Brassica crops.ResultsBoth somatic mosaic and germline mutations were efficiently created using the CRISPR/Cas9 system, and null mutant strains of Pxkmo and Pxcardinal were obtained. A frame-shift mutation in Pxkmo caused yellow compound eyes at adult stage while an in-frame mutation lacking two amino acids resulted in a hypomorphic red eye phenotypes. In contrast, Pxcardinal-deficient moths with a frame-shift mutation exhibited yellow eye pigmentation in newly emerged adults which turned to red as the adults aged. Additionally, differences were observed in the coloration of larval ocelli, brains and testes in Pxkmo and Pxcardinal yellow-eye mutant lines.ConclusionsOur work identifies the important roles of Pxkmo and Pxcardinal in P. xylostella eye pigmentation and provides tools for future genetic manipulation of this important crop pest.

Highlights

Eye pigmentation genes have been utilized as visible markers for constructing genetic control prototypes in several insect vectors of human disease
We identified the P. xylostella homologs of kmo and cardinal, which have been reported as important genes involved in ommochrome synthesis of mosquitoes and silkworm [13, 20, 24] and characterized their mutant phenotypes using the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system
Our work validates that the CRISPR/Cas9 system is highly active in diamondback moth (DBM) for generating site-specific mutations and suggests that improvements in the system can be achieved through the use of protein components

Summary

Introduction

Eye pigmentation genes have been utilized as visible markers for constructing genetic control prototypes in several insect vectors of human disease. Orthologs of two ommochrome pathway genes, kynurenine 3-hydroxylase (kmo) and cardinal, were investigated in Plutella xylostella, a globally distributed, economically important pest of Brassica crops. For example in Drosophila, these networks include the ommochrome and pteridine synthesis pathways, while ommochromes are the only visual pigments in other important species such as various mosquitoes, beetles and the silkworm Bombyx mori [12,13,14]. In the B. mori ommochrome synthesis pathway, the upstream component tryptophan is oxidized to formylkynurenine by tryptophan oxidase (encoded by vermilion in Drosophila), after which formylkynurenine is catalyzed into kynurenine by kynurenine formamidase (KFase). The 3-hydroxykynurenine is incorporated into pigment granules by a heterodimer composed of ABC transporters Scarlet and White and catalyzed into xanthommatin by Cardinal, which is involved in ommin synthesis (Fig. 1) [14, 15]

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