Genome assembly of the C4 grass Themeda triandra confirms karyotype orthology with sorghum and reveals genetic variation across diverse environments

Abstract

Themeda triandra (tribe Andropogoneae) is a pan-continental grass occurring throughout Australia. Recognising its remarkable adaptive capacity, we assembled the de novo nuclear genome sequence of a diploid accession from eastern Australia, finding all ten chromosomes of the 755 Mb assembly highly syntenic with those of Sorghum bicolor. Genotyping and cytometry of accessions from across the climatic range of Australia show geographically structured lineages, with polyploids dominating in arid regions, apart from a notable diploid lineage from the arid north-west of Australia. A detailed comparison of this arid-zone lineage with two diploids from temperate south-eastern Australia through whole-genome resequencing revealed extensive putative copy number variation and polymorphisms, with changes in orthologs of known flowering regulation genes in Sorghum consistent with the environmental origin of Themeda accessions. Exploration of the extensive adaptation and resultant genetic diversity in T. triandra is expected to benefit grassland management programs and enable introgression of novel genes into Andropogoneae crops for climate resilience.