MS1/MMD1 homologues in the moss Physcomitrium patens are required for male and female gametogenesis.

The Arabidopsis Plant HomeoDomain (PHD) proteins AtMS1 and AtMMD1 provide chromatin-mediated transcriptional regulation essential for tapetum-dependent pollen formation. This pollen-based male gametogenesis is a derived trait of seed plants. Male gametogenesis in the common ancestors of land plants is instead likely to have been reminiscent of that in extant bryophytes where flagellated sperms are produced by an elaborate gametophyte generation.

Dependence on clade II bHLH transcription factors for nursing of haploid products by tapetal-like cells is conserved between moss sporangia and angiosperm anthers.

Clade II basic helix-loop-helix transcription factors (bHLH TFs) are essential for pollen production and tapetal nursing functions in angiosperm anthers. As pollen has been suggested to be related to bryophyte spores by descent, we characterized two Physcomitrium (Physcomitrella) patens clade II bHLH TFs (PpbHLH092 and PpbHLH098), to test if regulation of sporogenous cells and the nursing cells surrounding them is conserved between angiosperm anthers and bryophyte sporangia. We made CRISPR-Cas9 reporter and loss-of-function lines to address the function of PpbHLH092/098.

The Physcomitrium patens egg cell expresses several distinct epigenetic components and utilizes homologues of BONOBO genes for cell specification.

Although land plant germ cells have received much attention, knowledge about their specification is still limited. We thus identified transcripts enriched in egg cells of the bryophyte model species Physcomitrium patens, compared the results with angiosperm egg cells, and selected important candidate genes for functional analysis. We used laser-assisted microdissection to perform a cell-type-specific transcriptome analysis on egg cells for comparison with available expression profiles of vegetative tissues and male reproductive organs.

Studies of moss reproductive development indicate that auxin biosynthesis in apical stem cells may constitute an ancestral function for focal growth control.

The plant hormone auxin is a key factor for regulation of plant development, and this function was probably reinforced during the evolution of early land plants. We have extended the available toolbox to allow detailed studies of how auxin biosynthesis and responses are regulated in moss reproductive organs, their stem cells and gametes to better elucidate the function of auxin in the morphogenesis of early land plants. We measured auxin metabolites and identified IPyA (indole-3-pyruvic acid) as the main biosynthesis pathway in Physcomitrium (Physcomitrella) patens and established knock-out, overexpressor and reporter lines for biosynthesis genes which were analyzed alongside previously reported auxin-sensing and transport reporters.

Minimal auxin sensing levels in vegetative moss stem cells revealed by a ratiometric reporter.

Efforts to reveal ancestral functions of auxin, a key regulator of plant growth and development, and its importance for evolution have been hampered by a fragmented picture of auxin response domains in early-diverging land plants. We report the mapping of auxin sensing and responses during vegetative moss development using novel reporters. We established a moss-specific ratiometric reporter (PpR2D2) for Auxin Response Element- and AUXIN RESPONSE FACTOR-independent auxin sensing in Physcomitrella patens, and its readout during vegetative development was compared with new promoter-based GmGH3::GFPGUS and DR5revV2::GFPGUS auxin response reporters.

/ Genes Affect Pre- and Post-meiotic Anther Processes in Auxin Sensing Domains in Arabidopsis.

In flowering plants, mature sperm cells are enclosed in pollen grains formed in structures called anthers. Several cell layers surrounding the central sporogenous cells of the anther are essential for directing the developmental processes that lead to meiosis, pollen formation, and the subsequent pollen release. The specification and function of these tissues are regulated by a large number of genetic factors.

Auxin Homeostasis in Arabidopsis Ovules Is Anther-Dependent at Maturation and Changes Dynamically upon Fertilization.

The plant hormone auxin is a vital component for plant reproduction as it regulates the development of both male and female reproductive organs, including ovules and gynoecia. Furthermore, auxin plays important roles in the development and growth of seeds and fruits. Auxin responses can be detected in ovules shortly after fertilization, and it has been suggested that this accumulation is a prerequisite for the developmental reprogramming of the ovules to seeds, and of the gynoecium to a fruit.

Auxin-mediated developmental control in the moss Physcomitrella patens.

The signalling molecule auxin regulates many fundamental aspects of growth and development in plants. We review and discuss what is known about auxin-regulated development in mosses, with special emphasis on the model species Physcomitrella patens. It is well established that mosses and other early diverging plants produce and respond to auxin.

Cytokinin-Auxin Crosstalk in the Gynoecial Primordium Ensures Correct Domain Patterning.

The Arabidopsis () gynoecium consists of two congenitally fused carpels made up of two lateral valve domains and two medial domains, which retain meristematic properties and later fuse to produce the female reproductive structures vital for fertilization. Polar auxin transport (PAT) is important for setting up distinct apical auxin signaling domains in the early floral meristem remnants allowing for lateral domain identity and outgrowth. Crosstalk between auxin and cytokinin plays an important role in the development of other meristematic tissues, but hormone interaction studies to date have focused on more accessible later-stage gynoecia and the spatiotemporal interactions pivotal for patterning of early gynoecium primordia remain unknown.

Autophagy is required for gamete differentiation in the moss Physcomitrella patens.

Autophagy, a major catabolic process in eukaryotes, was initially related to cell tolerance to nutrient depletion. In plants autophagy has also been widely related to tolerance to biotic and abiotic stresses (through the induction or repression of programmed cell death, PCD) as well as to promotion of developmentally regulated PCD, starch degradation or caloric restriction important for life span. Much less is known regarding its role in plant cell differentiation.

Transcriptomic Signature of the SHATTERPROOF2 Expression Domain Reveals the Meristematic Nature of Arabidopsis Gynoecial Medial Domain.

Plant meristems, like animal stem cell niches, maintain a pool of multipotent, undifferentiated cells that divide and differentiate to give rise to organs. In Arabidopsis (Arabidopsis thaliana), the carpel margin meristem is a vital meristematic structure that generates ovules from the medial domain of the gynoecium, the female floral reproductive structure. The molecular mechanisms that specify this meristematic region and regulate its organogenic potential are poorly understood.

Directional auxin transport mechanisms in early diverging land plants.

The emergence and radiation of multicellular land plants was driven by crucial innovations to their body plans. The directional transport of the phytohormone auxin represents a key, plant-specific mechanism for polarization and patterning in complex seed plants. Here, we show that already in the early diverging land plant lineage, as exemplified by the moss Physcomitrella patens, auxin transport by PIN transporters is operational and diversified into ER-localized and plasma membrane-localized PIN proteins.

Polar auxin transport is essential for medial versus lateral tissue specification and vascular-mediated valve outgrowth in Arabidopsis gynoecia.

Although it is generally accepted that auxin is important for the patterning of the female reproductive organ, the gynoecium, the flow as well as the temporal and spatial actions of auxin have been difficult to show during early gynoecial development. The primordium of the Arabidopsis (Arabidopsis thaliana) gynoecium is composed of two congenitally fused, laterally positioned carpel primordia bisected by two medially positioned meristematic regions that give rise to apical and internal tissues, including the ovules. This organization makes the gynoecium one of the most complex plant structures, and as such, the regulation of its development has remained largely elusive.

The MOSS Physcomitrella patens reproductive organ development is highly organized, affected by the two SHI/STY genes and by the level of active auxin in the SHI/STY expression domain.

In order to establish a reference for analysis of the function of auxin and the auxin biosynthesis regulators SHORT INTERNODE/STYLISH (SHI/STY) during Physcomitrella patens reproductive development, we have described male (antheridial) and female(archegonial) development in detail, including temporal and positional information of organ initiation. This has allowed us to define discrete stages of organ morphogenesis and to show that reproductive organ development in P. patens is highly organized and that organ phyllotaxis differs between vegetative and reproductive development.

Auxin and the Arabidopsis thaliana gynoecium.

Recent research is beginning to reveal how intricate networks of hormones and transcription factors coordinate the complex patterning of the gynoecium, the female reproductive structure of flowering plants. This review summarizes recent advances in understanding of how auxin biosynthesis, transport, and responses together generate specific gynoecial domains. This review also highlights areas where future research endeavours are likely to provide additional insight into the homeostatic molecular mechanisms by which auxin regulates gynoecium development.

Autophagy mediates caloric restriction-induced lifespan extension in Arabidopsis.

Caloric restriction (CR) extends lifespan in various heterotrophic organisms ranging from yeasts to mammals, but whether a similar phenomenon occurs in plants remains unknown. Plants are autotrophs and use their photosynthetic machinery to convert light energy into the chemical energy of glucose and other organic compounds. As the rate of photosynthesis is proportional to the level of photosynthetically active radiation, the CR in plants can be modeled by lowering light intensity.

SHORT INTERNODES/STYLISH genes, regulators of auxin biosynthesis, are involved in leaf vein development in Arabidopsis thaliana.

Leaves depend on highly developed venation systems to collect fixed carbon for transport and to distribute water. We hypothesized that local regulation of auxin biosynthesis plays a role in vein development. To this effect, we assessed the role of the SHORT INTERNODES/STYLISH (SHI/STY) gene family, zinc-finger transcription factors linked to regulation of auxin biosynthesis, in Arabidopsis thaliana leaf vein development.

The Arabidopsis thaliana transcriptional activator STYLISH1 regulates genes affecting stamen development, cell expansion and timing of flowering.

SHORT-INTERNODES/STYLISH (SHI/STY)-family proteins redundantly regulate development of lateral organs in Arabidopsis thaliana. We have previously shown that STY1 interacts with the promoter of the auxin biosynthesis gene YUCCA (YUC)4 and activates transcription of the genes YUC4, YUC8 and OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF (ORA)59 independently of protein translation. STY1 also affects auxin levels and auxin biosynthesis rates.

Expression of Arabidopsis SHORT INTERNODES/STYLISH family genes in auxin biosynthesis zones of aerial organs is dependent on a GCC box-like regulatory element.

Auxin/indole-3-acetic acid (IAA) biosynthesis in Arabidopsis (Arabidopsis thaliana) plays a major role in growth responses to developmental and genetic signals as well as to environmental stimuli. Knowledge of its regulation, however, remains rudimentary, and few proteins acting as transcriptional modulators of auxin biosynthesis have been identified. We have previously shown that alteration in the expression level of the SHORT INTERNODES/STYLISH (SHI/STY) family member STY1 affects IAA biosynthesis rates and IAA levels and that STY1 acts as a transcriptional activator of genes encoding auxin biosynthesis enzymes.

Transcriptome analysis of high-temperature stress in developing barley caryopses: early stress responses and effects on storage compound biosynthesis.

High-temperature stress, like any abiotic stress, impairs the physiology and development of plants, including the stages of seed setting and ripening. We used the Affymetrix 22K Barley1 GeneChip microarray to investigate the response of developing barley (Hordeum vulgare) seeds, termed caryopses, after 0.5, 3, and 6 h of heat stress exposure; 958 induced and 1122 repressed genes exhibited spatial and temporal expression patterns that provide a detailed insight into the caryopses' early heat stress responses.

Distinct and dynamic auxin activities during reproductive development.

Flowering plants have evolved sophisticated and complicated reproductive structures to ensure optimal conditions for the next generation. Successful reproduction relies on careful timing and coordination of tissue development, which requires constant communication between these tissues. Work on flower and fruit development over the last decade places the phytohormone auxin in a key role as a master of patterning and tissue specification of reproductive organs.

Significance of light, sugar, and amino acid supply for diurnal gene regulation in developing barley caryopses.

The caryopses of barley (Hordeum vulgare), as of all cereals, are complex sink organs optimized for starch accumulation and embryo development. While their early to late development has been studied in great detail, processes underlying the caryopses' diurnal adaptation to changes in light, temperature, and the fluctuations in phloem-supplied carbon and nitrogen have remained unknown. In an attempt to identify diurnally affected processes in developing caryopses at the early maturation phase, we monitored global changes of both gene expression and metabolite levels.

Homologues of the Arabidopsis thaliana SHI/STY/LRP1 genes control auxin biosynthesis and affect growth and development in the moss Physcomitrella patens.

The plant hormone auxin plays fundamental roles in vascular plants. Although exogenous auxin also stimulates developmental transitions and growth in non-vascular plants, the effects of manipulating endogenous auxin levels have thus far not been reported. Here, we have altered the levels and sites of auxin production and accumulation in the moss Physcomitrella patens by changing the expression level of homologues of the Arabidopsis SHI/STY family proteins, which are positive regulators of auxin biosynthesis genes.

The Arabidopsis thaliana STYLISH1 protein acts as a transcriptional activator regulating auxin biosynthesis.

The establishment and maintenance of auxin maxima in vascular plants is regulated by auxin biosynthesis and polar intercellular auxin flow. The disruption of normal auxin biosynthesis in mouse-ear cress (Arabidopsis thaliana) leads to severe abnormalities, suggesting that spatiotemporal regulation of auxin biosynthesis is fundamental for normal growth and development. We have shown previously that the induction of the SHORT-INTERNODES/STYLISH (SHI/STY) family member STY1 results in increased transcript levels of the YUCCA (YUC) family member YUC4 and also higher auxin levels and auxin biosynthesis rates in Arabidopsis seedlings.