The Land–Sea Connection: Insights Into the Plant Lineage from a Green Algal Perspective

Abstract

The colonization of land by plants generated opportunities for the rise of new heterotrophic life forms, including humankind. A unique event underpinned this massive change to earth ecosystems—the advent of eukaryotic green algae. Today, an abundant marine green algal group, the prasinophytes, alongside prasinodermophytes and nonmarine chlorophyte algae are facilitating insights into plant developments. Genome-level data allow identification of conserved proteins and protein families with extensive modifications, losses, or gains and expansion patterns that connect to niche specialization and diversification. Here, we contextualize attributes according to Viridiplantae evolutionary relationships, starting with orthologous protein families, and then focusing on key elements with marked differentiation, resulting in patchy distributions across green algae and plants. We place attention on peptidoglycan biosynthesis, important for plastid division and walls; phytochrome photosensors that are master regulators in plants; and carbohydrate-active enzymes, essential to all manner of carbohydrate biotransformations. Together with advances in algal model systems, these areas are ripe for discovering molecular roles and innovations within and across plant and algal lineages. Expected final online publication date for the Annual Review of Plant Biology, Volume 73 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Bacterial transcriptional response to labile exometabolites from photosynthetic picoeukaryote Micromonas commoda

“…CAZyme genes enriched in the transcriptome indicated catabolism or modifications of peptidoglycan and its components (CAZyme annotations CE11, GH23, GH25, GT51; Table 1 ). The full biosynthesis pathway for peptidoglycan synthesis is present in the closely-related species M. pusilla CCMP1545 (although peptidoglycan itself has not been detected), while the M. commoda pathway appears incomplete [ 54 ]. Nonetheless, several genes present in the M. commoda genome could generate peptidoglycan intermediates (MURE, MRAY, MURG, and PBP).…”

The Chloroplast Envelope of Angiosperms Contains a Peptidoglycan Layer

“…Another possibility that must be considered is the lack of homologs of penicillin-binding proteins (PBPs) in seed plant genomes. Although in all flowering plant genomes with "full PGN set-PBP" a coding region for a transglycosylase domain like in PBP was found, in none of these genomes a transpeptidase domain protein could be identified 15 to bind to ß-lactam antibiotics like in bacteria.…”

“…Analyzing mutants of MraY, MurG and DDL would be helpful to verify this theory. Interestingly, within one plant order, representatives with both pathway setups were found, for example in Brassicales with A. thaliana ("4-PGN set") and Carica papaya ("full PGN set-PBP") or in Rosales with Fragaria vesca ("4-PGN set") and Malus domestica ("full PGN set-PBP") 14,15 . The appearance of both PGN pathway types within closely related lineages implies convergent loss of genes in the "4-PGN set" species and supports the hypothesis of an alternative PGN synthesis pathway.…”

“…But recent studies have revealed that an almost full set of PGN synthesis (9 out of 10 genes except PBP; Fig. 1) is encoded in several genomes of mono-and dicotyledenous angiosperms 14,15 (from here on coined as "full PGN set-PBP"). Therefore, it is very likely that at least in these angiosperm species with a full PGN set-PBP PGN is synthesized.…”

Heme oxygenase-independent bilin biosynthesis revealed by a hmox1 suppressor screening in Chlamydomonas reinhardtii

“…Bilin biosynthesis is of great importance for photosynthetic organisms because of the essential roles of bilins in light sensing, photon capture, and photoacclimation ( Rockwell et al, 2014 ; Duanmu et al, 2017 ; Bachy et al, 2022 ). The Chlamydomonas hmox1 mutant is deficient in bilin biosynthesis due to the disruption of HMOX1 , although the PCYA1 protein accumulates at similar levels relative to wild-type 4A+ ( Duanmu et al, 2013 ).…”