Abstract
Studies of adaptation in the wild grass Anthoxanthum odoratum at the Park Grass Experiment (PGE) provided one of the earliest examples of rapid evolution in plants. Anthoxanthum has become locally adapted to differences in soil Al toxicity, which have developed there due to soil acidification from long-term experimental fertilizer treatments. In this study, we used transcriptome sequencing to identify Al stress responsive genes in Anthoxanhum and identify candidates among them for further molecular study of rapid Al tolerance evolution at the PGE. We examined the Al content of Anthoxanthum tissues and conducted RNA-sequencing of root tips, the primary site of Al induced damage. We found that despite its high tolerance Anthoxanthum is not an Al accumulating species. Genes similar to those involved in organic acid exudation (TaALMT1, ZmMATE), cell wall modification (OsSTAR1), and internal Al detoxification (OsNRAT1) in cultivated grasses were responsive to Al exposure. Expression of a large suite of novel loci was also triggered by early exposure to Al stress in roots. Three-hundred forty five transcripts were significantly more up- or down-regulated in tolerant vs. sensitive Anthoxanthum genotypes, providing important targets for future study of rapid evolution at the PGE.
Highlights
The Park Grass Experiment (PGE, Harpenden, UK) is a unique site where both radical changes in plant species composition and rapid evolution within populations have been documented in response to experimental soil manipulations over the past 150+ years
Al tolerance was measured as relative root growth (RRG) of replicate vegetative tillers removed from each greenhouse plant
We compared: wchange expression in the tolerant RNA-seq plant genotype with the average qPCR foldchange expression in four other tolerant genotypes, and expression in the sensitive RNA-seq genotype with three other sensitive genotypes (Fig A in S1 File). In both comparisons there was a significant positive relationship between expression change in the RNA-seq genotype and the average expression change measured via qPCR (Fig D in S1 File; tolerant plants, F(1,20) = 7.12, slope = 0.46 +/- 0.16, p = 0.013; sensitive plants, F(1,20) = 21.22, slope = 0.54 +/- 0.12, p
Summary
The Park Grass Experiment (PGE, Harpenden, UK) is a unique site where both radical changes in plant species composition and rapid evolution within populations have been documented in response to experimental soil manipulations over the past 150+ years. Since the initial tests of local adaptation to Al toxicity at the PGE, work on domesticated plants has yielded detailed molecular information on the basis of soil Al tolerance in domesticated grasses such as rice, wheat, sorghum and corn. This information provides a useful comparative resource for exploring the genetic basis of Al tolerance in wild grasses such as Anthoxanthum. Most cultivated plants have low to moderate Al tolerance and production is severely limited in acid soils For this reason, tolerance has been studied intensively in grasses such as sorghum, rice, wheat, and maize [14,15,16]. By comparing expression patterns between sensitive and tolerant Anthoxanthum genotypes, we highlight candidate genes of further interest in the ecological genetic study of rapid evolution at the PGE
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