Unexpected cryptic species among streptophyte algae most distant to land plants

Abstract

Streptophytes are one of the major groups of the green lineage (Chloroplastida or Viridiplantae). During one billion years of evolution, streptophytes have radiated into an astounding diversity of uni- and multicellular green algae as well as land plants. Most divergent from land plants is a clade formed by Mesostigmatophyceae, Spirotaenia spp. and Chlorokybophyceae. All three lineages are species-poor and the Chlorokybophyceae consist of a single described species, Chlorokybus atmophyticus. In this study, we used phylogenomic analyses to shed light into the diversity within Chlorokybus using a sampling of isolates across its known distribution. We uncovered a consistent deep genetic structure within the Chlorokybus isolates, which prompted us to formally extend the Chlorokybophyceae by describing four new species. Gene expression differences among Chlorokybus species suggest certain constitutive variability that might influence their response to environmental factors. Failure to account for this diversity can hamper comparative genomic studies aiming to understand the evolution of stress response across streptophytes. Our data highlight that future studies on the evolution of plant form and function can tap into an unknown diversity at key deep branches of the streptophytes.

The evolution of plant proton pump regulation via the R domain may have facilitated plant terrestrialization

“…However, as Klebsormidium can live in both water and soils 57 , 58 , in contrast to Chara which are exclusively aquatic algae, the lack in Chara of a PM H + -ATPase with an R domain may reflect gene loss. Chlorokyphoceae represented by its single species Chlorokybus atmophyticus live on soil and rock surfaces 59 but branched out very early and before the appearance of the R domain, and thus might have adopted differently to terrestrial conditions. Zygnemophyceae are the closest relatives to land plants 60 and PM H + -ATPases in this group have a fully developed R domain.…”

The APAF1_C/WD40 repeat domain-encoding gene from the sea lettuce Ulva mutabilis sheds light on the evolution of NB-ARC domain-containing proteins in green plants

“…For Streptophyta (S) (except Embryophytes), Chlorophyta (C), Prasinodermaphyta (P) and Glaucophyta (G), the taxonomic class and order of the studied species are according to AlgaeBase (Guiry and Guiry 2021 ). The nomenclature of C. melkonianii follows the recent revision of the Chlorokyboceae by Irisarri et al ( 2021 ). Numbers in brackets are fractions of the total number of species (some species include multiple accessions, see Supplementary Table S2) in which the depicted APAF1_C/WD40 module was positively identified, whereas red crosses indicate that no homologs were identified in the corresponding lineage.…”

Plastid DNA sequences and oospore characters of some European species ofTolypellasectionTolypella(Obtusifolia, Characeae) indicate a new crypticTolypellaspecies from the Mediterranean island Sardinia

“…The existence of cryptic species is very common for about half of all marine eukaryotic organisms such as Rhodophyta (e.g. Payo et al, 2013), Chlorophyta (Cimino and Delwiche, 2002, Irisarri et al, 2021) or Phaeophyceae (Poong et al, 2013). In order to get a robust description of morphological characters for discrimination between the two dioecious taxa, detailed analysis of a larger number of samples needs to be done.…”