Comparison of Mutations Induced by Different Doses of Fast-Neutron Irradiation in the M1 Generation of Sorghum (Sorghum bicolor)

Abstract

Sorghum is an important C₄ crop with various food and nonfood uses. Although improvements through hybridization and selection have been exploited, the introduction of genetic variation and the development of new genotypes in sorghum are still limited. Fast-neutron (FN) mutagenesis is a very effective method for gene functional studies and to create genetic variability. However, the full spectrum of FN-induced mutations in sorghum is poorly understood. To address this, we generated an FN-induced mutant population from the inbred line 'BTx623' and sequenced 40 M₁ seedlings to evaluate the mutagenic effects of FNs on sorghum. The results show that each line had an average of 43.7 single-base substitutions (SBSs), 3.7 InDels and 35.15 structural variations (SVs). SBSs accounted for approximately 90.0% of the total number of small mutations. Among the eight treatment groups, FN irradiation at a dose of 19 Gy generated the highest number of mutations. The ratio of transition/transversion ranged from 1.77 to 2.21, and the G/C to A/T transition was the most common substitution in all mutant lines. The distributions of the identified SBSs and InDels were similar and uneven across the genome. An average of 3.63 genes were mutated in each mutant line, indicating that FN irradiation resulted in a suitable density of mutated genes, which can be advantageous for improving elite material for one specific or a few traits. These results provide a basis for the selection of the suitable dose of mutagen and new genetic resources for sorghum breeding.

Keywords: fast-neutron irradiation; genetic variation; mutation; sorghum; whole-genome re-sequencing.

Figure 1

The number of each type of mutation in the eight treatment groups. SV, structural variation; InDel, insertion and deletion; SBS, single-base substitution.

Figure 2

FN irradiation-induced transitions and transversions in the eight treatment groups. Ti, transitions; Tv, transversions.

Figure 3

FN irradiation-induced InDels in the eight treatment groups. InDels, insertions and deletions; INS, insertion; DEL, deletion.

Figure 4

The number of SBSs, InDels and SVs in each chromosome induced by FN irradiation in the eight treatment groups. (a) FN irradiation-induced SBS mutations in each chromosome in the eight treatment groups. (b) FN irradiation-induced InDel mutations in each chromosome in the eight treatment groups. (c) FN irradiation-induced SV mutations in each chromosome in the eight treatment groups. SBSs, single-base substitutions; InDels, insertions and deletions; SVs, structural variations.

Figure 5

The distribution of InDel mutations across the genome in the 19 Gy-treated lines. InDel, insertion and deletion.