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Plant hormones modulate plant growth, development, and defense. However, many aspects of the origin and evolution of plant hormone signaling pathways remain obscure. Here, we use a comparative genomic and phylogenetic approach to investigate the origin and evolution of nine major plant hormone (abscisic acid, auxin, brassinosteroid, cytokinin, ethylene, gibberellin, jasmonate, salicylic acid, and strigolactone) signaling pathways. Our multispecies genome-wide analysis reveals that: (1) auxin, cytokinin, and strigolactone signaling pathways originated in charophyte lineages; (2) abscisic acid, jasmonate, and salicylic acid signaling pathways arose in the last common ancestor of land plants; (3) gibberellin signaling evolved after the divergence of bryophytes from land plants; (4) the canonical brassinosteroid signaling originated before the emergence of angiosperms but likely after the split of gymnosperms and angiosperms; and (5) the origin of the canonical ethylene signaling pathway postdates shortly the emergence of angiosperms. Our findings might have important implications in understanding the molecular mechanisms underlying the emergence of land plants.

The effect of nickel (Ni) on the generation of plant bioelectrical signals was evaluated in Nitellopsis obtusa, a Characean model organism. Conventional glass-microelectrode technique and K(+)-anaesthesia method in current-clamp and voltage-clamp modes were used for the measurement and analysis of electrical parameters. Ni(2+) treatment rapidly influenced the action potential (AP) parameters namely, excitation threshold, AP peak and duration, membrane potential at various voltages and dynamics of ion currents. We conclude that altered electrical signaling pathway in the test organism constituted the early target for Ni toxicity imposition. The observed Ni interference could be ascribed to disturbed [Ca(2+)]cyt content, impaired Cl(-) and K(+) channels activity resulting in decreased excitability and repolarization rate in generated AP.

Interaction of a HAMLET-like La–OA cytotoxic complex (human α-lactalbumin-oleic acid) and its constituents with the excitable plasmalemma of giant Chara corallina cells was investigated. The voltage–clamp technique was used to study Ca 2+ and Cl − transient currents in the plasmalemma of intact cells. The action of the complex and OA on the target cell membrane has a dose-dependent character. It was found that the La–OA complex has an inhibiting effect on Ca 2+ current across the plasmalemma, while α-lactalbumin alone does not affect the electrophysiological characteristics of the cellular membrane. However, oleic acid blocks Ca 2+ current across the plasmalemma. This is accompanied by the induction of a non-selective conductivity in the cellular membrane, a decrease in the resting potential and plasma membrane resistance of algal cells. We propose that the cytotoxicity of La–OA and other HAMLET-like complexes is determined by oleic acid acting as a blocker of potential-dependent Ca 2+ channels in the plasma membrane of target cells. The presented results show that the study model of green algae C. corallina cells plasmalemma is a convenient tool for the investigation of ion channels in many animal cells.

A pivotal step in the transformation of an endosymbiotic cyanobacterium to a plastid some 1.5 billion years ago was the evolution of a protein import apparatus, the TOC/TIC machinery, in the common ancestor of Archaeplastida. Recently, a putative new TIC member was identified in Arabidopsis thaliana: TIC214. This finding is remarkable for a number of reasons: (1) TIC214 is encoded by ycf1, so it would be the first plastid-encoded protein of this apparatus; (2) ycf1 is unique to the green lineage (Chloroplastida) but entirely lacking in glaucophytes (Glaucophyta) and the red lineage (Rhodophyta) of the Archaeplastida; (3) ycf1 has been shown to be one of the few indispensable plastid genes (aside from the ribosomal machinery), yet it is missing in the grasses; and (4) 30 years of previous TOC/TIC research missed it. These observations prompted us to survey the evolution of ycf1. We found that ycf1 is not only lacking in grasses and some parasitic plants, but also for instance in cranberry (Ericaceae). The encoded YCF proteins are highly variable, both in sequence length and in the predicted number of N-terminal transmembrane domains. The evolution of the TOC/TIC machinery in the green lineage experienced specific modifications, but our analysis does not support YCF1 to be a general green TIC. It remains to be explained how the apparent complete loss of YCF1 can be tolerated by some embryophytes and whether what is observed for YCF1 function in a member of the Brassicaceae is also true for, e.g., algal and noncanonical YCF1 homologs.

Plant phytochromes are photoswitchable red/far-red photoreceptors that allow competition with neighboring plants for photosynthetically active red light. In aquatic environments, red and far-red light are rapidly attenuated with depth; therefore, photosynthetic species must use shorter wavelengths of light. Nevertheless, phytochrome-related proteins are found in recently sequenced genomes of many eukaryotic algae from aquatic environments. We examined the photosensory properties of seven phytochromes from diverse algae: four prasinophyte (green algal) species, the heterokont (brown algal) Ectocarpus siliculosus, and two glaucophyte species. We demonstrate that algal phytochromes are not limited to red and far-red responses. Instead, different algal phytochromes can sense orange, green, and even blue light. Characterization of these previously undescribed photosensors using CD spectroscopy supports a structurally heterogeneous chromophore in the far-red–absorbing photostate. Our study thus demonstrates that extensive spectral tuning of phytochromes has evolved in phylogenetically distinct lineages of aquatic photosynthetic eukaryotes.

• The aims of this study were to investigate the appearance of strigolactones in the green lineage and to determine the primitive function of these molecules. • We measured the strigolactone content of several isolated liverworts, mosses, charophyte and chlorophyte green algae using a sensitive biological assay and LC‐MS/MS analyses. In parallel, sequence comparison of strigolactone‐related genes and phylogenetic analyses were performed using available genomic data and newly sequenced expressed sequence tags. The primitive function of strigolactones was determined by exogenous application of the synthetic strigolactone analog, GR24, and by mutant phenotyping. • Liverworts, the most basal Embryophytes and Charales, one of the closest green algal relatives to Embryophytes, produce strigolactones, whereas several other species of green algae do not. We showed that GR24 stimulates rhizoid elongation of Charales, liverworts and mosses, and rescues the phenotype of the strigolactone‐deficient Ppccd8 mutant of Physcomitrella patens. • These findings demonstrate that the first function of strigolactones was not to promote arbuscular mycorrhizal symbiosis. Rather, they suggest that the strigolactones appeared earlier in the streptophyte lineage to control rhizoid elongation. They may have been conserved in basal Embryophytes for this role and then recruited for the stimulation of colonization by glomeromycotan fungi.

To efficiently detect aquatic invasive species early in an invasion when control may still be possible, predictions about which locations are likeliest to be occupied are needed at fine scales but are rarely available. Occupancy modeling could provide such predictions given data of sufficient quality and quantity. We assembled a data set for the macroalga starry stonewort ( Nitellopsis obtusa ) across Minnesota and Wisconsin, USA, where it is a new and high-priority invader. We used these data to construct a multi-season, single-species spatial occupancy model that included biotic, abiotic, and movement-related predictors. Distance to the nearest access was an important occurrence predictor, highlighting the likely role boats play in spreading starry stonewort. Fetch and water depth also predicted occupancy. We estimated an average detection probability of 63% at sites with mean non- N. obtusa plant cover, declining to ~ 38% at sites with abundant plant cover, especially that of other Characeae. We recommend that surveyors preferentially search for starry stonewort in areas of shallow depth and high fetch close to boat accesses. We also recommend searching during late summer/early fall when detection is likelier. This study illustrates the utility of fine-scale occupancy modeling for predicting the locations of nascent populations of difficult-to-detect species.

Many cells exhibit large-scale active circulation of their entire fluid contents, a process termed cytoplasmic streaming. This phenomenon is particularly prevalent in plant cells, often presenting strikingly regimented flow patterns. The driving mechanism in such cells is known: myosin-coated organelles entrain cytoplasm as they process along actin filament bundles fixed at the periphery. Still unknown, however, is the developmental process that constructs the well-ordered actin configurations required for coherent cell-scale flow. Previous experimental works on streaming regeneration in cells of Characean algae, whose longitudinal flow is perhaps the most regimented of all, hint at an autonomous process of microfilament self-organization driving the formation of streaming patterns during morphogenesis. Working from first principles, we propose a robust model of streaming emergence that combines motor dynamics with both microscopic and macroscopic hydrodynamics to explain how several independent processes, each ineffectual on its own, can reinforce to ultimately develop the patterns of streaming observed in the Characeae and other streaming species.

A number of mechanisms result in a feedback between water clarity and macrophytes and, consequently, the occurrence of alternative stable states in shallow lakes. We hypothesize that bottom-up mechanisms and interactions within the benthic food web are more important in a charophyte-dominated clear-water state, while top-down mechanism and interactions in the planktonic food web prevail at angiosperm dominance. Charophytes, which dominate at lower nutrient concentrations and develop higher densities than most angiosperms, can have a higher influence on sedimentation, resuspension, and water column nutrients. During dominance of dense submerged vegetation like charophytes, zooplankton can be hampered by low food quality and quantity and by high predation pressure from juvenile fish, which in turn are favoured by the high refuge potential of this vegetation. Grazing pressure from zooplankton on phytoplankton can therefore be low in charophytes, but the main feedback in angiosperm-dominated ecosystems. Charophytes offer a higher surface than most angiosperms to periphyton, which favors benthic invertebrates. These support macrophytes by grazing periphyton and constitute a central link in a trophic cascade from fish to periphyton and macrophytes. To test these hypotheses, more experiments and field measurements comparing the effect of charophytes and angiosperms on water clarity are needed.

In Europe, the genus Tolypella (Characeae) comprises four to eight Tolypella taxa in sections Rothia and Tolypella that have been distinguished by vegetative morphology and gametangial characters such as antheridial size and oospore wall ornamentation. However, morphological differentiation is difficult in some cases due to overlapping and variable vegetative features, which in many cases are difficult to observe clearly. To clarify the taxonomic status of the five European taxa of Tolypella in section Tolypella, sequence data of the plastid genes atpB, rbcL and psbC for Tolypella glomerata (Desv.) Leonh., Tolypella hispanica Allen, Tolypella nidifica (O.F. Müll.) A. Braun, Tolypella normaniana (Nordst.) Nordst. and Tolypella salina Cor. were combined with data on oospore morphology, including oospore wall ornamentation. Gene sequence data identified five distinct clusters, but they were not consistent with the morphologically identified five taxa. T. glomerata consisted of some of the samples morphologically identified as T. glomerata and seven samples of T. normaniana, while the remaining T. glomerata samples clustered with specimens of unclear affiliation (Tolypella sp.). We identified two clusters of T. hispanica within the European material: cluster T. hispanica I consisted of samples from various locations, whereas the second cluster (T. hispanica II) consisted of samples of T. hispanica from Sardinia Island. The remaining cluster consisted of all the specimens that had been determined as T. salina or T. nidifica in addition to two specimens of T. normaniana. Oospore morphology was most clearly distinguishable for T. glomerata. Oospore characteristics for all other taxa were not as informative but showed some geographical and/or environmentally influenced differences, especially for T. nidifica and T. salina. Our results suggest the need to further check the different taxonomy of Tolypella sect. Tolypella in which specimens normally identified as T. glomerata might be two different taxa, T. glomerata and an unidentified taxon; T. nidifica and T. salina are not separate taxa; T. normaniana is a diminutive variant of two different Tolypella taxa; and T. hispanica comprises two different taxa, one from the Mediterranean island Sardinia.