Carbon-concentrating mechanisms are a key trait in lichen ecology and distribution.

Carbon-concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs ([C44-carbon compound] and crassulacean acid metabolism [CAM]) is associated with significant shifts, most often to hot, dry and bright, or aquatic environments. If and how CCMs drive distributions of other terrestrial photosynthetic organisms, remains little studied. Lichens are ecologically important obligate symbioses between fungi and photosynthetic organisms. The primary photosynthetic partner in these symbioses can include CCM-presenting cyanobacteria (as carboxysomes), CCM-presenting green algae (as pyrenoids) or green algae lacking any CCM. We use an extensive dataset of lichen communities from eastern North America, spanning a wide climatic range, to test the importance of CCMs as predictors of lichen ecology and distribution. We show that the presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and different responses in cyanobacterial lichens. These responses contrast with our understanding of lichen physiology, whereby CCMs mitigate carbon limitation by water saturation at the cost of efficient use of vapor hydration. This study demonstrates that CCM status is a key functional trait in obligate lichen symbioses, equivalent in importance to its role in vascular plants, and central for studying present and future climate responses.

Co-expression network analyses of anthocyanin biosynthesis genes in Ruellia (Wild Petunias; Acanthaceae).

BACKGROUND: Anthocyanins are major pigments contributing to flower coloration and as such knowledge of molecular architecture underlying the anthocyanin biosynthetic pathway (ABP) is key to understanding flower color diversification. To identify ABP structural genes and associated regulatory networks, we sequenced 16 transcriptomes generated from 10 species of Ruellia and then conducted co-expression analyses among resulting data. RESULTS: Complete coding sequences for 12 candidate structural loci representing eight genes plus nine candidate regulatory loci were assembled. Analysis of non-synonymous/synonymous (dn/ds) mutation rates indicated all identified loci are under purifying selection, suggesting overall selection to prevent the accumulation of deleterious mutations. Additionally, upstream enzymes have lower rates of molecular evolution compared to downstream enzymes. However, site-specific tests of selection yielded evidence for positive selection at several sites, including four in F3'H2 and five in DFR3, and these sites are located in protein binding regions. A species-level phylogenetic tree constructed using a newly implemented hybrid transcriptome-RADseq approach implicates several flower color transitions among the 10 species. We found evidence of both regulatory and structural mutations to F3'5'H in helping to explain the evolution of red flowers from purple-flowered ancestors. CONCLUSIONS: Sequence comparisons and co-expression analyses of ABP loci revealed that mutations in regulatory loci are likely to play a greater role in flower color transitions in Ruellia compared to mutations in underlying structural genes.

Evolution of apetaly in the cosmopolitan genus Stellaria.

PREMISE: Apetaly is widespread across distantly related lineages of flowering plants and is associated with abiotic (or self-) pollination. It is particularly prevalent in the carnation family, and the cosmopolitan genus Stellaria contains many lineages that are hypothesized to have lost petals from showy petalous ancestors. But the pollination biology of apetalous species of Stellaria remains unclear. METHODS: Using a substantial species-level sampling (~92% of known taxonomic diversity), we describe the pattern of petal evolution within Stellaria using ancestral character state reconstructions. To help shed light on the reproductive biology of apetalous Stellaria, we conducted a field experiment at an alpine tundra site in the southern Rocky Mountains to test whether an apetalous species (S. irrigua) exhibits higher levels of selfing than a sympatric, showy petalous congener (S. longipes). RESULTS: Analyses indicated that the ancestor of Stellaria was likely showy petalous and that repeated, parallel reductions of petals occurred in clades across much of the world, with uncommon reversal back to showy petals. Field experiments supported high rates of selfing in the apetalous species and high rates of outcrossing in the petalous species. CONCLUSIONS: Petal loss is rampant across major clades of Stellaria and is potentially linked with self-pollination worldwide. Self-pollination occurs within the buds in S. irrigua, and high propensities for this and other forms of selfing known in many other taxa of arctic-alpine habitats may reflect erratic availability of pollinators.