An algal PIP-like aquaporin facilitates water transport and ionic conductance

Aquaporins are water and solute channel proteins found throughout the kingdoms of life. Ion-conducting aquaporins (icAQPs) have been identified in both plants and animals indicating that this function may be conserved through evolution. In higher plants icAQP function has been demonstrated for isoforms from two of five aquaporin subfamilies indicating that this function could have existed before the divergence of higher plants from green algae. Here a PIP-like aquaporin from the charophytic alga Klebsormidium nitens was functionally characterised in Xenopus laevis oocytes and its expression was found to induce water and ion conductance.

Origin and evolution of jasmonate signaling

Jasmonate (JA) signaling is a key mediator of plant development and defense which arose during plants transition from an aqueous to terrestrial environment. Elucidating the evolution of JA signaling is important for understanding plant development, defense, and production of specialized metabolites. The lineage of key protein domains characterizing JA signaling factors was traced to identify the origins of CORONITINE INSENSITIVE 1 (COI1), JASMONATE ZIM-DOMAIN (JAZ), NOVEL INTERACTOR OF JAZ, MYC2, TOPLESS, and MEDIATOR SUBUNIT 25. Charophytes do not possess genes encoding key JA signaling components, including COI1, JAZ, MYC2, and the JAZ-interacting bHLH factors, yet their orthologs are present in bryophytes. TIFY family genes were found in charophyta and chlorophya algae. JAZs evolved from ZIM genes of the TIFY family through changes to several key amino acids. Dating placed the origin of JA signaling 515 to 473 million years ago during the middle Cambrian to early Ordovician periods. This time is known for rapid biodiversification and mass extinction events. An increased predation from the diversifying and changing fauna may have driven evolution of JA signaling and plant defense.

Endomembrane architecture and dynamics during secretion of the extracellular matrix of the unicellular charophyte, Penium margaritaceum

The extracellular matrix (ECM) of many charophytes, the assemblage of green algae that are the sister group to land plants, is complex, produced in large amounts, and has multiple essential functions. An extensive secretory apparatus and endomembrane system are presumably needed to synthesize and secrete the ECM, but structural details of such a system have not been fully characterized. Penium margaritaceum is a valuable unicellular model charophyte for studying secretion dynamics. We report that Penium has a highly organized endomembrane system, consisting of 150-200 non-mobile Golgi bodies that process and package ECM components into different sets of vesicles that traffic to the cortical cytoplasm, where they are transported around the cell by cytoplasmic streaming. At either fixed or transient areas, specific cytoplasmic vesicles fuse with the plasma membrane and secrete their constituents. Extracellular polysaccharide (EPS) production was observed to occur in one location of the Golgi body and sometimes in unique Golgi hybrids. Treatment of cells with brefeldin A caused disruption of the Golgi body, and inhibition of EPS secretion and cell wall expansion. The structure of the endomembrane system in Penium provides mechanistic insights into how extant charophytes generate large quantities of ECM, which in their ancestors facilitated the colonization of land.

Three-dimensional growth: a developmental innovation that facilitated plant terrestrialization

One of the most transformative events in the history of life on earth was the transition of plants from water to land approximately 470 million years ago. Within the Charophyte green algae, the closest living relatives of land plants, body plans have evolved from those that comprise simple unicells to those that are morphologically complex, large and multicellular. The Charophytes developed these broad ranging body plans by exploiting a range of one-dimensional and two-dimensional growth strategies to produce filaments, mats and branches. When plants were confronted with harsh conditions on land, they were required to make significant changes to the way they shaped their body plans. One of the fundamental developmental transitions that occurred was the evolution of three-dimensional growth and the acquisition of apical cells with three or more cutting faces. Plants subsequently developed a range of morphological adaptations (e.g. vasculature, roots, flowers, seeds) that enabled them to colonise progressively drier environments. 3D apical growth also evolved convergently in the brown algae, completely independently of the green lineage. This review summarises the evolving developmental complexities observed in the early divergent Charophytes all the way through to the earliest conquerors of land, and investigates 3D apical growth in the brown algae.

Three rings for the evolution of plastid shape: a tale of land plant FtsZ

Nuclear-encoded plant FtsZ genes are derived from endosymbiotic gene transfer of cyanobacteria-like genes. The green lineage (Chloroplastida) and red lineage (Rhodophyta) feature FtsZ1 and FtsZ2 or FtsZB and FtsZA, respectively, which are involved in plastid division. These two proteins show slight differences and seem to heteropolymerize to build the essential inner plastid division ring. A third gene, encoding FtsZ3, is present in glaucophyte and charophyte algae, as well as in land plants except ferns and angiosperms. This gene was probably present in the last common ancestor of the organisms united by having a primary plastid (Archaeplastida) and was lost during vascular plant evolution as well as in the red and green algae. The presence/absence pattern of FtsZ3 mirrors that of a full set of Mur genes and the peptidoglycan wall encoded by them. Based on these findings, we discuss a role for FtsZ3 in the establishment or maintenance of plastid peptidoglycan shells.