The first chromosome‐scale assemblies for North American members of the Acer genus, sugar maple (Acer saccharum) and boxelder (Acer negundo), as well as transcriptomic evaluation of the abiotic stress response in A. saccharum are reported. This integrated study describes in‐depth aspects contributing to each species' approach to tolerance and applies current knowledge in many areas of plant genome biology with Acer physiology to help convey the genomic complexities underlying tolerance in broadleaf tree species.
Maples (the genus Acer) represent important and beloved forest, urban, and ornamental trees distributed throughout the Northern hemisphere. They exist in a diverse array of native ranges and distributions, across spectrums of tolerance or decline, and have varying levels of susceptibility to biotic and abiotic stress. Among Acer species, several stand out in their importance to economic interest. Here we report the first two chromosome-scale genomes for North American species, Acer negundo and Acer saccharum. Both assembled genomes contain scaffolds corresponding to 13 chromosomes, with A. negundo at a length of 442 Mb, an N50 of 32 Mb, and 30 491 genes, and A. saccharum at a length of 626 Mb, an N50 of 46 Mb, and 40 074 genes. No recent whole genome duplications were detected, though A. saccharum has local gene duplication and more recent bursts of transposable elements, as well as a large-scale translocation between two chromosomes. Genomic comparison revealed that A. negundo has a smaller genome with recent gene family evolution that is predominantly contracted and expansions that are potentially related to invasive tendencies and tolerance to abiotic stress. Examination of RNA sequencing data obtained from A. saccharum given long-term aluminum and calcium soil treatments at the Hubbard Brook Experimental Forest provided insights into genes involved in the aluminum stress response at the systemic level, as well as signs of compromised processes upon calcium deficiency, a condition contributing to maple decline.
Keywords: Acer negundo; Acer saccharum; abiotic stress; aluminum; calcium; differential expression; genome; nutrient stress; plasticity; tolerance.