Genetic analysis of the barley variegation mutant, grandpa1.a

Abstract

Background Providing the photosynthesis factory for plants, chloroplasts are critical for crop biomass and economic yield. However, chloroplast development is a complicated process, coordinated by the cross-communication between the nucleus and plastids, and the underlying biogenesis mechanism has not been fully revealed. Variegation mutants have provided ideal models to identify genes or factors involved in chloroplast development. Well-developed chloroplasts are present in the green tissue areas, while the white areas contain undifferentiated plastids that are deficient in chlorophyll. Unlike albino plants, variegation mutants survive to maturity and enable investigation into the signaling pathways underlying chloroplast biogenesis. The allelic variegated mutants in barley, grandpa 1 (gpa1), have long been identified but have not been genetically characterized. Results We characterized and genetically analyzed the grandpa1.a (gpa1.a) mutant. The chloroplast ultrastructure was evaluated using transmission electron microscopy (TEM), and it was confirmed that chloroplast biogenesis was disrupted in the white sections of gpa1.a. To determine the precise position of Gpa1, a high-resolution genetic map was constructed. Segregating individuals were genotyped with the barley 50 k iSelect SNP Array, and the linked SNPs were converted to PCR-based markers for genetic mapping. The Gpa1 gene was mapped to chromosome 2H within a gene cluster functionally related to photosynthesis or chloroplast differentiation. In the variegated gpa1.a mutant, we identified a large deletion in this gene cluster that eliminates a putative plastid terminal oxidase (PTOX). Conclusions Here we characterized and genetically mapped the gpa1.a mutation causing a variegation phenotype in barley. The PTOX-encoding gene in the delimited region is a promising candidate for Gpa1. Therefore, the present study provides a foundation for the cloning of Gpa1, which will elevate our understanding of the molecular mechanisms underlying chloroplast biogenesis, particularly in monocot plants.

Identification and function analysis of yellow-leaf mutant (YX-yl) of broomcorn millet

“…The photosynthetic rate and chloroplast ultrastructure are directly affected by leaf color mutations [ 4 , 8 , 13 , 14 , 41 ]. In a leaf-color mutant of rice, the chloroplasts are degrade, the matrix is disordered, and the thylakoids almost completely disappear [ 4 ].…”

“…Studies have elucidated the molecular mechanisms of leaf-color mutants, especially the yellowing phenotype, which is most commonly observed in higher plants. Yellow-leaf mutants usually have shorter plant height, lower grain yield, deficiency in photosynthetic pigments, and abnormal chloroplast ultramicrostructures compared with the wild type [7,[11][12][13][14]. For example, the yellowish-leaf mutant ydl of rice has photosynthetic pigment deficiencies, degraded chloroplasts, and disordered matrix [4].…”

Plastid terminal oxidase is required for chloroplast biogenesis in barley

“…The gpa1 mutation causes a striped pattern on the leaf of the variegation mutant, associated with a semi‐dwarf and overtillering phenotype (Figures 1A–C). Using F 2 s derived from a cross between Bowman and BW397, we have anchored the Gpa1 gene to a ~ 350 kb region on chromosome 2H (chr2H:653355700.0.653689834, MorexV3) delimited by markers M19 and M8 (Figure 1D) (Yang et al., 2021). Gene annotation identified a total of 18 putative protein‐coding genes (Table S1).…”

“…Of those, G13 and G15 encode a DNA topoisomerase (or gyrase) and a ubiquinol oxidase, respectively. Because of the known roles played by DNA topoisomerase and ubiquinol oxidase in chloroplast biogenesis, G13 and G15 were selected as strong candidates of Gpa1 (Carol et al., 1999; Wall et al., 2004; Wu et al., 1999; Yang et al., 2021).…”

“…The gpa1.a mutation was originally identified in a spontaneous mutant of Barley cv Lyallpur, and a near‐isogenic line (NIL) of Bowman, BW397 displaying the variegation phenotype, was developed by backcrossing (Druka et al., 2011). Genetic mapping anchored Gpa1 onto the long arm of chromosome 2H within a gene cluster functionally related to photosynthesis or chloroplast differentiation (Druka et al., 2011; Matchett et al., 1971; Yang et al., 2021). However, the underlying gene for Gpa1 was not identified.…”