An almost uncharacterized area of plant biology is the complement of organisms that live mutually with plant communities, or the metagenome. In many plants, the acquisition of inorganic minerals is facilitated by an active network of mycorrhizal associations between soil fungal species and plant roots. However, assessing how these fungal and plant species interact has been hampered by the fact that many fungal species cannot be cultured. The advent of high throughput sequencing has enabled an unprecedented opportunity to identify the genomic changes induced through these communal relationships. Ruzicka et al. (2013, this issue) use high throughput sequencing to characterize the transcriptomes of both the tomato genome and its arbuscular mycorrhizal fungal symbiont in the field (Ruzicka et al., 2013). Instead of culturing the symbiont, a metagenomic sequencing strategy was employed where RNA from a wild-type tomato plant and a mutant for reduced mycorrhizal colonization were sequenced and bioinfomatically separated. This metagenomic analysis revealed a suite of genes for transport and cell wall remodeling required for the symbiotic relationship. Metagenomic sequencing will open up the opportunity to explore additional symbiotic relationships and further functionally characterize aspects of the genome that are not innate to the genome sequence.
Future Plant Genomes
The first ∼50 plant genomes have provided a glimpse at the gene number, types and numbers of repeats, and how genomes grow and contract. However, we are just at the beginning of defining the functional aspects of plant genomes. To reach the goal of breeding better plants for future food, clothing, and energy, we will need to expand both the species sequenced, the number of species re-sequenced, and the type of omics data layered on genomes. Currently only one gymnosperm has been sequenced and no CAM (Crassulacean acid metabolism) photosynthetic plants have been sequenced. While we have come a long way over the past 13 yr since the publication of the Arabidopsis genome, we still have a long way to go before we will be able to engineer the plant of the future.