Quantitative trait locus mapping combined with variant and transcriptome analyses identifies a cluster of gene candidates underlying the variation in leaf wax between upland and lowland switchgrass ecotypes

• Published in: Theoretical and applied genetics Vol. 134; no. 7; pp. 1957 - 1975
• Main Authors: Qi, Peng, Pendergast, Thomas H., Johnson, Alex, Bahri, Bochra A., Choi, Soyeon, Missaoui, Ali, Devos, Katrien M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2021; Springer; Springer Nature B.V; Springer Nature
• Subjects: Acyl carrier protein; Agriculture; Analysis; BASIC BIOLOGICAL SCIENCES; Biochemistry; Biomass energy; Biomedical and Life Sciences; Biotechnology; Cenchrus ciliaris; Chromosome 7; Chromosome Mapping; Chromosomes; Ecotype; Ecotypes; Environmental aspects; Foliar diagnosis; Gene Expression Profiling; Gene mapping; Genes; Genetic aspects; Genetic Linkage; Genetics & heredity; Genotypes; Growth; Hydrophobicity; Leaves; Life Sciences; Methods; Original; Original Article; Panicum - chemistry; Panicum - genetics; Panicum virgatum; Phenotype; Plant Biochemistry; Plant Breeding/Biotechnology; Plant Genetics and Genomics; Plant Leaves - chemistry; Plant sciences; Polyketide synthase; Polymorphism, Single Nucleotide; Production processes; Quantitative Trait Loci; Tetraploidy; Thioesterase; Transcriptome; Transcriptomes; Waxes - chemistry; United States
• ISSN: 0040-5752; 1432-2242
• DOI: 10.1007/s00122-021-03798-y

Key message Mapping combined with expression and variant analyses in switchgrass, a crop with complex genetics, identified a cluster of candidate genes for leaf wax in a fast-evolving region of chromosome 7K. Switchgrass ( Panicum virgatum L.) is a promising warm-season candidate energy crop. It occurs in two ecotypes, upland and lowland, which vary in a number of phenotypic traits, including leaf glaucousness. To initiate trait mapping, two F 2 mapping populations were developed by crossing two different F 1 sibs derived from a cross between the tetraploid lowland genotype AP13 and the tetraploid upland genotype VS16, and high-density linkage maps were generated. Quantitative trait locus (QTL) analyses of visually scored leaf glaucousness and of hydrophobicity of the abaxial leaf surface measured using a drop shape analyzer identified highly significant colocalizing QTL on chromosome 7K (Chr07K). Using a multipronged approach, we identified a cluster of genes including Pavir.7KG077009, which encodes a Type III polyketide synthase-like protein, and Pavir.7KG013754 and Pavir.7KG030500, two highly similar genes that encode putative acyl-acyl carrier protein (ACP) thioesterases, as strong candidates underlying the QTL. The lack of homoeologs for any of the three genes on Chr07N, the relatively low level of identity with other switchgrass KCS proteins and thioesterases, as well as the organization of the surrounding region suggest that Pavir.7KG077009 and Pavir.7KG013754/Pavir.7KG030500 were duplicated into a fast-evolving chromosome region, which led to their neofunctionalization. Furthermore, sequence analyses showed all three genes to be absent in the two upland compared to the two lowland accessions analyzed. This study provides an example of and practical guide for trait mapping and candidate gene identification in a complex genetic system by combining QTL mapping, transcriptomics and variant analysis.