A broader model for C ₄ photosynthesis evolution in plants inferred from the goosefoot family (Chenopodiaceae s.s.)

Abstract

C 4 photosynthesis is a fascinating example of parallel evolution of a complex trait involving multiple genetic, biochemical and anatomical changes. It is seen as an adaptation to deleteriously high levels of photorespiration. The current scenario for C 4 evolution inferred from grasses is that it originated subsequent to the Oligocene decline in CO 2 levels, is promoted in open habitats, acts as a pre-adaptation to drought resistance, and, once gained, is not subsequently lost. We test the generality of these hypotheses using a dated phylogeny of Amaranthaceae s.l. (including Chenopodiaceae), which includes the largest number of C 4 lineages in eudicots. The oldest chenopod C 4 lineage dates back to the Eocene/ Oligocene boundary, representing one of the first origins of C 4 in plants, but still corresponding with the Oligocene decline of atmospheric CO 2 . In contrast to grasses, the rate of transitions from C 3 to C 4 is highest in ancestrally drought resistant (salt-tolerant and succulent) lineages, implying that adaptation to dry or saline habitats promoted the evolution of C 4 ; and possible reversions from C 4 to C 3 are apparent. We conclude that the paradigm established in grasses must be regarded as just one aspect of a more complex system of C 4 evolution in plants in general.

Repeated evolution of salt-tolerance in grasses

“…The classic example is asexuality which arises often but is rarely shared by all members of large, deep clades, leading to suggestions that asexual species lack the genetic variation needed for long-term evolutionary persistence [21]. It has also been suggested that lineages in saline environments may have increased extinction rates [19]. Third, a highly labile trait could show a tippy pattern if it is often gained and lost.…”

“…Chenopodacieae; [19]), most origins of salt-tolerance in grasses are close to the tips of the phylogeny. Most major groups of grasses contain some halophyte species, typically arising from a relatively large number of origins rather than clustering together (see the electronic supplementary material, figure S3), so that most salt-tolerant species have few close halophytic relatives.…”

Cytosine Methylation of an Ancient Satellite Family in the Wild Beet <b><i>Beta procumbens</i></b>

“…This is also demonstrated by the occurrence of pEV as a moderately repetitive and highly diverged repeat in C. quinoa . Because the split of the Betoideae and Chenopodioideae was estimated 52.7 MYA [Kadereit et al, 2012], we speculate that the pEV satellite might be older than 50-60 million years, characterizing pEV as an ancient satellite family that occurs in species of Betoideae and Chenopodioideae. In Anemone blanda , the age of a satellite DNA family was estimated to be 27 million years [Hagemann et al, 1993] suggesting that satellite families in plant genomes are already present for millions of years.…”

Pollen morphology of some species of Amaranthaceae s. lat. common in Italy

“…have long been considered two closely related families of the order Caryophyllales and they were subject to taxonomical revisions from the time they were first described to the present (Iamonico 2008(Iamonico , 2012(Iamonico , 2014Kadereit & al. 2003Kadereit & al. , 2012.…”