Fine Mapping and Candidate Gene Analysis of BnC08.cds, a Recessive Gene Responsible for Sepal-Specific Chlorophyll-Deficiency in Brassica napus L.

Wei Zhang,Hongli Zhu,Jiefu Zhang,Song Chen,Rui Shi,Chengming Sun,Feng Chen,Xiaoying Zhou,Xiaodong Wang,Maolong Hu

doi:10.3389/fpls.2022.850330

Abstract

Chloroplast development is crucial for photosynthesis and plant growth and many factors are involved in its regulation. The regulatory mechanism differs in different green tissues, and previous studies have focused on chloroplasts in leaves. In this study, a mutant with sepal-specific chlorophyll-deficiency was observed in Brassica napus and named as df74. Genetic analysis indicated that the phenotype was controlled by a single recessive nuclear gene. The gene was located on chromosome C08 by bulked-segregant analysis with whole-genome sequencing, which was designated as BnC08.cds. To fine-map the BnC08.cds, a F2 population was created from the cross of df74 and Zhongshuang11 (ZS11). Finally, the BnC08.cds was fine-mapped in the region between the single-nucleotide polymorphism (SNP) markers M5 and M6, corresponding to a 228.72 kb interval of the B. napus “ZS11” genome. Eighteen genes were predicted in the target region, and it was speculated that BnaC08G0442100ZS was the most likely candidate gene based on the results of transcriptome analyses and sequence variation analyses. These results provide a foundation to explore the regulation of chloroplast development in sepals.

Highlights

Green tissues are the photosynthetic organs in plants and their color is affected by the chlorophyll (Chl) content, which is the key factor for photomorphogenesis and photosynthesis
To investigate how the mutation affects chloroplast development, we observed the ultrastructure of the chloroplasts in the sepals of df74 and Ningyou 18 (NY18) with transmission electron microscopy (TEM)
In the cells of NY18, the chloroplasts were neatly arranged beside the cell walls and contained well-developed thylakoid membrane systems (Figures 3A,C)

Summary

Introduction

Green tissues are the photosynthetic organs in plants and their color is affected by the chlorophyll (Chl) content, which is the key factor for photomorphogenesis and photosynthesis. The mutation of any gene in this process may affect the content of Chl, so color mutants can readily form in artificial or spontaneous mutagenesis. The mutants are diverse, such as etiolation (Zhu et al, 2014), albino (Wang et al, 2016), white to green (Zhao et al, 2013; Ma et al, 2017), and stay-green (Jiang et al, 2007) These mutants are important for the study of Chl biosynthesis. The factors involved in Chl content can be roughly divided into three categories: biosynthesis and degradation of Chl, metabolism of heme, and chloroplast development. The biosynthesis of Chl and heme are two branches of the tetrapyrrole biosynthetic pathway. They share precursors from 5-aminolevulinic acid to protoporphyrin IX, and they inhibit each other. Mutations in any one of the genes may cause the blocking of chloroplast development and lead to color mutation

Methods

Results

Conclusion