Teresa Rose

and 10 more

To prevent yield losses caused by climate change it is important to identify naturally tolerant genotypes with traits and related pathways that can be targeted for crop improvement. Here we report on the characterization of contrasting vegetative heat tolerance in two UK bread wheat varieties. Under chronic heat stress, the heat-tolerant cultivar Cadenza produced an excessive number of tillers which translated into more spikes and higher grain yield compared to heat-sensitive Paragon. RNAseq and metabolomics analyses revealed a set of about 400 heat-responsive genes common to both genotypes. Only 71 genes showed a genotype x temperature interaction. As well as known heat-responsive genes such as HSPs, several genes that have not been previously linked to the heat response, particularly in wheat, have been identified, including several dehydrins, a number of ankyrin-repeat protein-encoding genes, and lipases. Over 5000 genotype-specific genes were identified, including photosynthesis-related genes which might explain the observed ability of Cadenza to maintain photosynthetic rate under heat stress. Contrary to primary metabolites, secondary metabolites showed a highly differentiated heat response and genotypic differences. These included e.g., benzoxazinoid (DIBOA, DIMBOA) but in particular phenylpropanoids and flavonoids with known radical scavenging capacity, which was assessed via the DPPH assay. The most highly heat-induced metabolite was (glycosylated) propanediol, which is widely used in industry as an anti-freeze. To our knowledge this is the first report on its response to stress in plants. The identified metabolites and candidate genes provide novel targets for the development of heat tolerant wheat.

Todd Gaines

and 9 more

Amaranthus palmeri is a widespread glyphosate-resistant (GR) weed in the USA. Since 2015, GR populations of A. palmeri have been confirmed in South America, raising the prospect of an ongoing invasion. We used RAD-Seq genotyping to explore genetic differentiation amongst A. palmeri populations from Brazil, Argentina and Uruguay. We also quantified gene copy number amplification of the glyphosate target, 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS) and the presence of an extra-chromosomal circular DNA (eccDNA) replicon in these populations. Genetic analyses indicated that populations in Brazil, Argentina, and Uruguay were only weakly differentiated (pairwise FST  0.043) in comparison to USA populations. STRUCTURE analysis did, however, assign Argentinean populations to a discrete cluster to those from Brazil and Uruguay. Neither elevated EPSPS copy number, nor the eccDNA EPSPS replicon were present in Argentinean populations, this being consistent with recent observations of other GR mechanisms in Argentina, and an independent in situ evolution of glyphosate resistance. Elevated EPSPS copy number and the EPSPS replicon were identified in all populations from Brazil and Uruguay. The presence of this mechanism and the very high sequence similarity of the EPSPS replicon to that found in the USA are strongly suggestive of the recent invasion of GR into Brazil and Uruguay. Our results are consistent with a single introduction of A. palmeri into South America sometime before the 1980s, and subsequent local evolution of GR in Argentina but with a secondary invasion of GR A. palmeri from the USA into Brazil and Uruguay during the 2010’s.