Whole Genome Sequencing of a Sorghum Mutant with Low Carbon Isotope Discrimination

Recent efforts to engineer C4 photosynthetic traits into C3 plants such as rice demand an understanding of genetic elements that enable C4 plants to outperform C3 plants. As a part of the C4 rice consortium's efforts to identify genes needed to support C4 photosynthesis, EMS mutagenized sorghum populations were generated and screened to identify genes that cause a loss of C4 function. A stable carbon isotope ratios (d13C) of leaf dry matter has been used to distinguish between species with C3 and C4 photosynthetic pathways. Here we report the identification of a sorghum (Sorghum bicolor) mutant with a low d13C characteristic. A mutant (named Mut33) with a pale phenotype and stunted growth was identified from an EMS treated sorghum M2 population. The stable carbon isotope analysis of the mutants showed a decrease of 13C uptake capacity. The mutant was back-crossed to its wildtype (WT). Fertile BC1F1 progenies of the cross between the low d13C mutant and its WT were like the WT parent in terms of 13C values and phenotypes. Gas exchange measurements of the low d13C sorghum mutants showed a higher CO2 compensation point (25.24 µmol CO2.mol-1air) 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 d13C BC1F2 mutant plants. These were sequenced using an Illumina platform.