A sorghum (Sorghum bicolor) mutant with altered carbon isotope ratio

Recent efforts to engineer C(4) photosynthetic traits into C(3) plants such as rice demand an understanding of the genetic elements that enable C(4) plants to outperform C(3) plants. As a part of the C(4) Rice Consortium’s efforts to identify genes needed to support C(4) photosynthesis, EMS mutagenized sorghum populations were generated and screened to identify genes that cause a loss of C(4) function. Stable carbon isotope ratio (δ(13)C) of leaf dry matter has been used to distinguishspecies with C(3) and C(4) photosynthetic pathways. Here, we report the identification of a sorghum (Sorghum bicolor) mutant with a low δ(13)C characteristic. A mutant (named Mut33) with a pale phenotype and stunted growth was identified from an EMS treated sorghum M(2) population. The stable carbon isotope analysis of the mutants showed a decrease of (13)C uptake capacity. The noise of random mutation was reduced by crossing the mutant and its wildtype (WT). The back-cross (BC(1)F(1)) progenies were like the WT parent in terms of (13)C values and plant phenotypes. All the BC(1)F(2) plants with low δ(13)C died before they produced their 6(th) leaf. Gas exchange measurements of the low δ(13)C sorghum mutants showed a higher CO(2) compensation point (25.24 μmol CO(2).mol(-1)air) and the maximum rate of photosynthesis was less than 5μmol.m(-2).s(-1). To identify the genetic determinant of this trait, four DNA pools were isolated; two each from normal and low δ(13)C BC(1)F(2) mutant plants. These were sequenced using an Illumina platform. Comparison of allele frequency of the single nucleotide polymorphisms (SNPs) between the pools with contrasting phenotype showed that a locus in Chromosome 10 between 57,941,104 and 59,985,708 bps had an allele frequency of 1. There were 211 mutations and 37 genes in the locus, out of which mutations in 9 genes showed non-synonymous changes. This finding is expected to contribute to future research on the identification of the causal factor differentiating C(4) from C(3) species that can be used in the transformation of C(3) to C(4) plants.