Singlet oxygen (1O2) refers to the lowest excited electronic state of molecular oxygen. It easily oxidizes biological molecules and, therefore, is cytotoxic. In plant cells, 1O2 is formed mostly in the light in thylakoid membranes by reaction centers of photosystem II. In high concentrations, 1O2 destroys membranes, proteins and DNA, inhibits protein synthesis in chloroplasts leading to photoinhibition of photosynthesis, and can result in cell death. However, 1O2 also acts as a signal relaying information from chloroplasts to the nucleus, regulating expression of nuclear genes. In spite of its extremely short lifetime, 1O2 can diffuse from the chloroplasts into the cytoplasm and the apoplast. As shown by recent studies, 1O2-activated signaling pathways depend not only on the levels but also on the sites of 1O2 production in chloroplasts, and can activate two types of responses, either acclimation to high light or programmed cell death. 1O2 can be produced in high amounts also in root cells during drought stress. This review summarizes recent advances in research on mechanisms and sites of 1O2 generation in plants, on 1O2-activated pathways of retrograde- and cellular signaling, and on the methods to study 1O2 production in plants.

https://www.mdpi.com/1422-0067/21/9/3237/pdf

Singlet Oxygen in Plants: Generation, Detection, and Signaling Roles.

Mounting evidence from genomic and transcriptomic studies suggests that most genetic networks regulating the morphogenesis of land plant sporophytes were co-opted and modified from those already present in streptophyte algae and gametophytes of bryophytes sensu lato. However, thus far, no candidate genes have been identified that could be responsible for "planation", a conversion from a three-dimensional to a two-dimensional growth pattern. According to the telome theory, "planation" was required for the genesis of the leaf blade in the course of leaf evolution. The key transcription factors responsible for leaf blade development in angiosperms are YABBY proteins, which until recently were thought to be unique for seed plants. Yet, identification of a YABBY homologue in a green alga and the recent findings of YABBY homologues in lycophytes and hornworts suggest that YABBY proteins were already present in the last common ancestor of land plants. Thus, these transcriptional factors could have been involved in "planation", which fosters our understanding of the origin of leaves. Here, we summarise the current data on functions of YABBY proteins in the vegetative and reproductive development of diverse angiosperms and gymnosperms as well as in the development of lycophytes. Furthermore, we discuss a putative role of YABBY proteins in the genesis of multicellular shoot apical meristems and in the evolution of leaves in early divergent terrestrial plants.

YABBY Genes in the Development and Evolution of Land Plants

Bryophytes including mosses, liverworts, and hornworts are among the earliest land plants, and occupy a crucial phylogenetic position to aid in the understanding of plant terrestrialization. Despite their small size and simple structure, bryophytes are the second largest group of extant land plants. They live ubiquitously in various habitats and are highly diversified, with adaptive strategies to modern ecosystems on Earth. More and more genomes and transcriptomes have been assembled to address fundamental questions in plant biology. Here, we review recent advances in bryophytes associated with diversity, phylogeny, and ecological adaptation. Phylogenomic studies have provided increasing supports for the monophyly of bryophytes, with hornworts sister to the Setaphyta clade including liverworts and mosses. Further comparative genomic analyses revealed that multiple whole-genome duplications might have contributed to the species richness and morphological diversity in mosses. We highlight that the biological changes through gene gain or neofunctionalization that primarily evolved in bryophytes have facilitated the adaptation to early land environments; among the strategies to adapt to modern ecosystems in bryophytes, desiccation tolerance is the most remarkable. More genomic information for bryophytes would shed light on key mechanisms for the ecological success of these 'dwarfs' in the plant kingdom. 

OUP accepted manuscript

Organelles-nucleus-plasmodesmata signaling (ONPS): an update on its roles in plant physiology, metabolism and stress responses.

The plastid evolved from a symbiotic cyanobacterial ancestor and is an essential organelle for plant life, but its developmental roles in roots have been largely overlooked. Here, we show that plastid translation is connected to the stem cell patterning in lateral root primordia. The RFC3 gene encodes a plastid-localized protein that is a conserved bacterial ribosomal protein S6 of β/γ proteobacterial origin. The rfc3 mutant developed lateral roots with disrupted stem cell patterning and associated with decreased leaf photosynthetic activity, reduced accumulation of plastid rRNAs in roots, altered root plastid gene expression, and changes in expression of several root stem cell regulators. These results suggest that deficiencies in plastid function affect lateral root stem cells. Treatment with the plastid translation inhibitor spectinomycin phenocopied the defective stem cell patterning in lateral roots and altered plastid gene expression observed in the rfc3 mutant. Additionally, when prps17 defective in a plastid ribosomal protein was treated with low concentrations of spectinomycin, it also phenocopied the lateral root phenotypes of rfc3 The spectinomycin treatment and rfc3 mutation also negatively affected symplasmic connectivity between primary root and lateral root primordia. This study highlights previously unrecognized functions of plastid translation in the stem cell patterning in lateral roots.

/pdf/plastid-translation-is-essential-for-lateral-root-stem-cell-3bzc5mfteu.pdf

Plastid translation is essential for lateral root stem cell patterning in Arabidopsis thaliana.

In plants, organogenesis and specification of cell layers and tissues rely on precise symplastic delivery of regulatory molecules via plasmodesmata. Accordingly, abundance and aperture of plasmodesmata at individual cell boundaries should be controlled by the plant. Recently, studies in Arabidopsis established reactive oxygen species as major regulators of plasmodesmata formation and gating. We show that in a barley mutant deficient in the synthesis of chlorophyll b, the numbers of plasmodesmata in leaves and in the shoot apical meristem are significantly higher than in the corresponding wild type, probably due to redox imbalance in the mutant. The resulting disturbance of symplasmic transport is likely to be the reason for the observed delayed floral transition in these mutants.

https://www.tandfonline.com/doi/pdf/10.1080/15592324.2017.1300732

Chlorophyllide-a-Oxygenase (CAO) deficiency affects the levels of singlet oxygen and formation of plasmodesmata in leaves and shoot apical meristems of barley.

What can the phylogeny of class I KNOX genes and their expression patterns in land plants tell us about the evolution of shoot development

Transfer of developmental regulators, such as miRNA and transcription factors, through plasmodesmata represents one of the key mechanisms regulating morphogenesis in angiosperms. This mechanism has been termed non-cell-autonomous regulation. At present it is not known whether this process is involved in the morphogenesis of plants belonging to the evolutionarily ancient taxa. Importantly, structure and symplastic organization of apical meristems in the representatives of such taxa significantly differ from those in flowering plants. The non-cell-autonomous transcription factors encoded by the KNOX genes which regulate functions of the shoot apical meristem may become a promising model to study this issue. Refs 102. Figs 3.

/pdf/molecular-and-cellular-aspects-of-the-shoot-apical-meristems-wfc7g71nr6.pdf

Molecular and cellular aspects of the shoot apical meristems organization of vascular plants

The review represents an analysis of recent year publications in connection with preventive and therapeutic use of postbiotics (PB). Postbiotics are widely used as immunomodulators, anti-inflammatory agents, protectors and the normalizers of metabolism of the open cavity mucosal biotopes, liver, brain and other organs, tissues and innate immunity cell populations that co-function to intestinal microbial metabolites as a network (cofunction within a number of metabolic axes “intestine-other locations”). They act in combination with other effectors as auxiliary agents prolonging the effect of drugs and supporting them. Prophylactic and therapeutic uses of PB are directed against groups of intestinal infection diseases, hepatitis, tumors, neurodegenerative brain disorders, other metabolic disorders and pathologies. New aspects of research of PB include the study and application of recognizing and binding therapeutic PB according to and in connection with a network of “Probiotic lectins—Glycoconjugates” interactions. The data indicate the prospects of a search and application of the new groups and combinations of PB directed at glycoconjugate exposed targets in accompanying and supportive therapy. Probiotic bifidobacteria, lactobacilli, baker’s yeast and probiotic lectins are perspective resources of synergistic sets of metabolite-cellular PB against diseases, pathologies and groups of infections.

Ekaterina A. Klimova

Papers

Chlorophyllide-a-Oxygenase (CAO) deficiency affects the levels of singlet oxygen and formation of plasmodesmata in leaves and shoot apical meristems of barley.

What can the phylogeny of class I KNOX genes and their expression patterns in land plants tell us about the evolution of shoot development

Molecular and cellular aspects of the shoot apical meristems organization of vascular plants

Postbiotics as factors against diseases along metabolic axes