Abstract
C4 photosynthesis and Crassulacean acid metabolism (CAM) have been considered as largely independent adaptations despite sharing key biochemical modules. Portulaca is a geographically widespread clade of over 100 annual and perennial angiosperm species that primarily use C4 but facultatively exhibit CAM when drought stressed, a photosynthetic system known as C4 + CAM. It has been hypothesized that C4 + CAM is rare because of pleiotropic constraints, but these have not been deeply explored. We generated a chromosome-level genome assembly of Portulaca amilis and sampled mRNA from P. amilis and Portulaca oleracea during CAM induction. Gene co-expression network analyses identified C4 and CAM gene modules shared and unique to both Portulaca species. A conserved CAM module linked phosphoenolpyruvate carboxylase to starch turnover during the day-night transition and was enriched in circadian clock regulatory motifs in the P. amilis genome. Preservation of this co-expression module regardless of water status suggests that Portulaca constitutively operate a weak CAM cycle that is transcriptionally and posttranscriptionally upregulated during drought. C4 and CAM mostly used mutually exclusive genes for primary carbon fixation, and it is likely that nocturnal CAM malate stores are shuttled into diurnal C4 decarboxylation pathways, but we found evidence that metabolite cycling may occur at low levels. C4 likely evolved in Portulaca through co-option of redundant genes and integration of the diurnal portion of CAM. Thus, the ancestral CAM system did not strongly constrain C4 evolution because photosynthetic gene networks are not co-regulated for both daytime and nighttime functions.
Abstract from the paper’s OpenAlex record, shown for indexing and research. Copyright remains with the authors or the publisher. Read at the source ↗
The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.
Claims 5
Claim · model-written summary
A chromosome-level genome assembly of Portulaca amilis was generated.
- Taxon
- Portulaca amilis
Portulaca amilise0 - Outcome
- chromosome-level genome assemblye0
- Value
- chromosome-levele0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We generated a chromosome-level genome assembly of Portulaca amilis”
Claim · model-written summary
Co-expression analysis identified shared and unique C4 and CAM gene modules in two Portulaca species.
- Outcome
- C4 and CAM gene modules shared and uniquee0
PortulacaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gene co-expression network analyses identified C4 and CAM gene modules shared and unique to both Portulaca species.”
Claim · model-written summary
The conserved CAM module was enriched in circadian clock regulatory motifs.
- Taxon
- P. amilisPortulaca amilise0
- Outcome
- circadian clock regulatory motifse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“was enriched in circadian clock regulatory motifs in the P. amilis genome”
Claim · model-written summary
Module preservation across water states suggested constitutive weak CAM activity with drought upregulation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Preservation of this co-expression module regardless of water status suggests that Portulaca constitutively operate a weak CAM cycle that is transcriptionally and posttranscriptionally upregulated during drought.”
Claim · model-written summary
The authors inferred C4 evolution by redundant gene co-option and integration of diurnal CAM.
- Outcome
- C4 likely evolvede0
- Qualifier
- co-option of redundant genes and integration of the diurnal portion of CAMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“C4 likely evolved in Portulaca through co-option of redundant genes and integration of the diurnal portion of CAM”