Characterization of novel Sorghum brown midrib mutants from an EMS-mutagenized population.
Bottom Line: In sorghum (Sorghum bicolor (L.) Moench) and several other C4 grasses, brown midrib (bmr) mutants have been shown to reduce lignin concentration.Overall, most of the identified bmr lines showed reduced lignin concentration of their biomass relative to wild-type (WT).Like bmr2, bmr6, and bmr12, these mutants may affect monolignol biosynthesis and may be useful for bioenergy and forage improvement when stacked together or in combination with the three previously described bmr alleles.
Affiliation: Grain, Forage and Bioenergy Research Unit, USDA-ARS, Lincoln, Nebraska 68583 Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, Nebraska 68583 Scott.Sattler@ars.usda.gov.Show MeSH
Mentions: In the greenhouse, putative bmr mutant lines were crossed to cytoplasmic male-sterile lines representing the three previously described bmr loci, bmr2, bmr6, and bmr12, and the leaf midrib phenotype of F1 progeny and mutant lines were visually scored when the plants were approximately 0.5 m tall (Table 1). Through this visual examination, the midribs of 23 of the lines were determined to fall within the naturally observed range of midrib color, and to not have a brown midrib phenotype (Table S2). For three lines, the results of these test-crosses were inconclusive (Table S2). In addition, one allele of bmr2, nine alleles of bmr6, and four alleles of bmr12 were identified based on leaf phenotype of the F1 progeny (Figure 2 and Table 1). The line number was incorporated into the allelic designation for these previously described bmr loci—bmr2, bmr6, or bmr12. The mutations responsible for the bmr2-2, bmr12-30, bmr12-34, bmr12-35, and bmr12-820 alleles isolated were characterized and reported previously (Saballos et al. 2012; Sattler et al. 2012). In addition, there were six mutant lines with bmr leaf phenotypes that were not allelic to bmr2, bmr6, or bmr12. The leaf midrib phenotypes of these six mutant lines were similar to the previously described loci bmr2, bmr6, or bmr12, although brown coloration was not dark as bmr6 midrib (Figure 3). Additional crosses between these six lines were performed and the F1 progeny were scored for the bmr leaf midrib phenotype to determine allelism among them (Table 2). The results of these test-crosses indicated that the six bmr mutant lines (29, 100, 122, 1107, 1168, and 1937) represent four novel loci (Figure 2), which we named bmr29 through bmr32 to avoid overlap with the designators bmr1 through bmr28 for bmr mutants previously isolated at Purdue University in the 1970s (Porter et al. 1978; Saballos et al. 2008). Mutant line 41 was excluded from this group because its leaf phenotype and the results of the allelism tests were inconsistent (Table 2). In summary, 20 lines appear to carry mutations responsible for the bmr leaf midrib phenotype.
Affiliation: Grain, Forage and Bioenergy Research Unit, USDA-ARS, Lincoln, Nebraska 68583 Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, Nebraska 68583 Scott.Sattler@ars.usda.gov.