Toward finally unraveling the phylogenetic relationships of Juncaceae with respect to another cyperid family, Cyperaceae.

Juncaceae is a cosmopolitan family belonging to the cyperid clade of Poales together with Cyperaceae and Thurniaceae. These families have global economic and ethnobotanical significance and are often keystone species in wetlands around the world, with a widespread cosmopolitan distribution in temperate and arctic regions in both hemispheres. Currently, Juncaceae comprises more than 474 species in eight genera: Distichia, Juncus, Luzula, Marsippospermum, Oreojuncus, Oxychloë, Patosia and Rostkovia. The phylogeny of cyperids has not been studied before in a complex view based on most sequenced species from all three families. In this study, most sequenced regions from chloroplast (rbcL, trnL, trnL-trnF) and nuclear (ITS1-5.8S-ITS2) genomes were employed from more than a thousand species of cyperids covering all infrageneric groups from their entire distributional range. We analyzed them by maximum parsimony, maximum likelihood, and Bayesian inference to revise the phylogenetic relationships in Juncaceae and Cyperaceae. Our major results include the delimitation of the most problematic paraphyletic genus Juncus, in which six new genera are recognized and proposed to recover monophyly in this group: Juncus, Verojuncus, gen. nov., Juncinella, gen. et stat. nov., Alpinojuncus, gen. nov., Australojuncus, gen. nov., Boreojuncus, gen. nov. and Agathryon, gen. et stat. nov. For these genera, a new category, Juncus supragen. et stat. nov., was established. This new classification places most groups recognized within the formal Juncus clade into natural genera that are supported by morphological characters.

Heat stress response mechanisms in pollen development.

Being rooted in place, plants are faced with the challenge of responding to unfavourable local conditions. One such condition, heat stress, contributes massively to crop losses globally. Heatwaves are predicted to increase, and it is of vital importance to generate crops that are tolerant to not only heat stress but also to several other abiotic stresses (e.g. drought stress, salinity stress) to ensure that global food security is protected. A better understanding of the molecular mechanisms that underlie the temperature stress response in pollen will be a significant step towards developing effective breeding strategies for high and stable production in crop plants. While most studies have focused on the vegetative phase of plant growth to understand heat stress tolerance, it is the reproductive phase that requires more attention as it is more sensitive to elevated temperatures. Every phase of reproductive development is affected by environmental challenges, including pollen and ovule development, pollen tube growth, male-female cross-talk, fertilization, and embryo development. In this review we summarize how pollen is affected by heat stress and the molecular mechanisms employed during the stress period, as revealed by classical and -omics experiments.

Characterization of ALBA Family Expression and Localization in Arabidopsis thaliana Generative Organs.

ALBA DNA/RNA-binding proteins form an ancient family, which in eukaryotes diversified into two Rpp25-like and Rpp20-like subfamilies. In most studied model organisms, their function remains unclear, but they are usually associated with RNA metabolism, mRNA translatability and stress response. In plants, the enriched number of ALBA family members remains poorly understood. Here, we studied ALBA dynamics during reproductive development in Arabidopsis at the levels of gene expression and protein localization, both under standard conditions and following heat stress. In generative tissues, ALBA proteins showed the strongest signal in mature pollen where they localized predominantly in cytoplasmic foci, particularly in regions surrounding the vegetative nucleus and sperm cells. Finally, we demonstrated the involvement of two Rpp25-like subfamily members ALBA4 and ALBA6 in RNA metabolism in mature pollen supported by their co-localization with poly(A)-binding protein 3 (PABP3). Collectively, we demonstrated the engagement of ALBA proteins in male reproductive development and the heat stress response, highlighting the involvement of ALBA4 and ALBA6 in RNA metabolism, storage and/or translational control in pollen upon heat stress. Such dynamic re-localization of ALBA proteins in a controlled, developmentally and environmentally regulated manner, likely reflects not only their redundancy but also their possible functional diversification in plants.

Evolutionary history of callose synthases in terrestrial plants with emphasis on proteins involved in male gametophyte development.

Callose is a plant-specific polysaccharide (ß-1,3-glucan) playing an important role in angiosperms in many developmental processes and responses to biotic and abiotic stresses. Callose is synthesised at the plasma membrane of plant cells by callose synthase (CalS) and, among others, represents the main polysaccharide in the callose wall surrounding the tetrads of developing microspores and in the growing pollen tube wall. CalS proteins involvement in spore development is a plesiomorphic feature of terrestrial plants, but very little is known about their evolutionary origin and relationships amongst the members of this protein family. We performed thorough comparative analyses of callose synthase family proteins from major plant lineages to determine their evolutionary history across the plant kingdom. A total of 1211 candidate CalS sequences were identified and compared amongst diverse taxonomic groups of plants, from bryophytes to angiosperms. Phylogenetic analyses identified six main clades of CalS proteins and suggested duplications during the evolution of specialised functions. Twelve family members had previously been identified in Arabidopsis thaliana. We focused on five CalS subfamilies directly linked to pollen function and found that proteins expressed in pollen evolved twice. CalS9/10 and CalS11/12 formed well-defined clades, whereas pollen-specific CalS5 was found within subfamilies that mostly did not express in mature pollen vegetative cell, although were found in sperm cells. Expression of five out of seven mature pollen-expressed CalS genes was affected by mutations in bzip transcription factors. Only three subfamilies, CalS5, CalS10, and CalS11, however, formed monophyletic, mostly conserved clades. The pairs CalS9/CalS10, CalS11/CalS12 and CalS3 may have diverged after angiosperms diversified from lycophytes and bryophytes. Our analysis of fully sequenced plant proteins identified new evolutionary lineages of callose synthase subfamilies and has established a basis for understanding their functional evolution in terrestrial plants.