Today’s guest post was contributed by Alessandra Decorato, a freelance science writer based in Vancouver, British Columbia. Read more of her work at alllessandradicorato.com.
The sacred fir tree grows at high altitudes along the Trans-Mexican Volcanic Belt, an arc of volcanoes that stretches across central-southern Mexico. Sacred fir forests help sequester carbon, stabilize soil, capture and filter water, and are a favorite winter habitat for monarch butterflies.
But near Mexico City, these trees are threatened by exposure to high levels of ozone, which is produced by burning fossil fuels in the city and blown outward by winds from mountain passes. An estimated 35% of fir trees around Mexico City show signs of ozone damage, including reddish needles that drop years earlier and increased susceptibility to insects.
Now, new research in G3: Genes|Genomes
Researchers at the Universidad Nacional Autónoma de México and Kew Royal Botanic Gardens in the UK have created a linkage map for the sacred fir tree. This type of map shows how often genes are inherited together, which is particularly useful for understanding large and repetitive genomes such as conifers. The map—created by sequencing DNA from seeds of two trees in different regions outside Mexico City—presented 5,881 coding genes, of which about 2,000 had known functions in conifers.
Armed with this map, the researchers returned to gene expression data they had previously collected from a forest west of Mexico City where there is chronic air pollution and both healthy and ozone-damaged trees can be found. Among the genes in the linkage map, they identified three clusters of genes with highly correlated expression and eight genes with significantly different expression between healthy and damaged trees, including genes that play a role in how other plants respond to ozone exposure.
Clustered genes also encode proteins with similar functions. This is consistent with an earlier theory that suggests that genes that are part of the same metabolic pathway or response are located close to each other, allowing organisms to regulate genes together and react quickly to threats such as pathogens. Focusing on these gene clusters in sacred fir could help scientists identify trees that are more ozone tolerant for reforestation efforts in regions with high levels of ozone pollution.
More broadly, the researchers say the approach highlights the potential of combining evolutionary genomics and RNA sequencing to shed light on how forest trees respond to sudden environmental threats and could be extended to study drought or soil pollution in other conifers.
