Spontaneous mutation in OsABCI8 caused an albino rice mutant induced by transplanting

Abstract

Spontaneous mutations play a key role in plant evolution. In this study, we identified and characterized albino rice mutants in an F₂ population derived from a cross between the japonica elite line Hwaseong and the introgression line CR5029, which carries chromosome segments from Oryza grandiglumis. Among 440 F₂ plants, ten exhibited an albino phenotype after transplantation, which was not observed in the parental lines, suggesting that either novel allelic combinations or spontaneous mutations may be responsible. QTL-seq analysis identified a major locus, qALB11, on chromosome 11, with a 1-bp T deletion in the Os11g0490800 (OsABCI8) gene as the most likely causal mutation. This deletion resulted in a truncated protein lacking the ABC domain, potentially affecting its function. Protein structure modeling confirmed structural differences between the mutant and wild-type proteins. Further genome-wide screening identified 669 spontaneous variants in the progeny population, many of which were associated with repeat sequences. These findings not only elucidate the genetic basis of a conditional albino phenotype but also highlight the broader role of spontaneous mutations and genome instability in plastid development and environmental stress adaptation in rice.

Keywords: Albino; Rice; Spontaneous mutation; Transplanting.

Fig. 1

Identification of albino plants after transplanting. (A) F₂ albino plants observed in the field. Red arrows indicate albino plants. (B) Seedling of albino plant sampled from field. White scale bar indicates 1 cm.

Fig. 2

QTL-seq analysis result when Hwaseong sequence was used as reference. Red, blue, and black lines indicated SNP-indices for delta, non-albino bulk, and albino bulk. Two significant loci were detected on chromosome 11 and 12 at p < 0.01.

Fig. 3

Fine mapping of qALB11. Approximately 240 Kb region was mapped for qALB11 using 209 F₃ plants.

Fig. 4

Sequence analysis of OsABCI8 that is responsible for albino phenotype. (A) Graphical gene structure with three different transcript forms. A 1-bp deletion was shown with red box and * indicated location of frameshifting stop codon. (B) Confirmation and comparison of 1-bp deletion using Sanger sequencing method. Red boxes indicate the deletion in albino plant. (C) Development of dCAPs marker (dCAPs_Albino) to screen 1-bp deletion in the segregating albino and normal plants. (D) Alignment of predicted protein sequence between transcripts of normal plant and albino plant.

Fig. 5

Protein structure prediction and pairwise structure alignment of OsABCI8.2. (A, B) Visualization of predicted alignment error of wild type (OsABCI8.2) and albino plant(OsABCI8-AL), (C, D) Predicted protein structure of OsABCI8.2 and OsABCI8-AL generated by ColabFold. (E) Alignment of two protein structures. (F) Alignment result of two predicted protein structures.