Low temperature is a major environmental stress factor that limits male reproductive success in plants; however, the mechanistic basis of pollen responses to different degrees of low temperature stress remains poorly understood. In this study, we investigated the cytological, biochemical, and molecular responses of tea (Camellia sinensis) pollen grains to low-temperature stress by germinating pollen in vitro at 15, 10, and 5°C. Although pollen germination rate and pollen tube length were reduced under all low-temperature treatments compared with the control, the underlying regulatory responses differed significantly with the severity of low-temperature stress. At 15°C, decreases in non-enzymatic antioxidants and stress-related proteins indicated an overall metabolic weakening, while the concomitant accumulation of callose, cellulose, and methyl-esterified pectins reflected an early structural adjustment of the pollen tube cell wall. At 10°C, the increasing stress load was partially counterbalanced by the induction of enzymatic antioxidant activities, and continued cell wall reinforcement identified this temperature as a transitional state between metabolic limitation and coordinated defense activation. In contrast, exposure to 5°C resulted in pronounced metabolic suppression, together with a shift of stress-related proteins toward membrane fractions and enhanced deposition of callose, cellulose, and particularly de-esterified acidic pectins, leading to increased cell wall rigidity and mechanical restriction of pollen tube elongation. Overall, this study demonstrates that low-temperature stress constrains pollen tube growth not through a single limiting factor but via a temperature-dependent reorganization of interconnected cytological, biochemical, and molecular mechanisms.

Key messageSHATTERPROOF 2 regulates TAA1 expression for the establishment of the gynoecium valve margins.Gynoecium development and patterning play a crucial role in determining the ultimate structure of the fruit and, thus, seed production. The MADS-box transcription factor SHATTERPROOF 2 (SHP2) contributes to valve margin differentiation and plays a major role in fruit dehiscence and seed dispersal. Despite the acknowledged contribution of auxin to gynoecium development, its precise role in valve margin establishment remains somewhat enigmatic. Our study addresses this gap by uncovering the role of SHP2 as a positive regulator of key auxin biosynthetic genes, TAA1 and YUCCA 4. Genetic and molecular analyses revealed that SHP2 directly regulates the expression of TAA1 in the valve margins of a stage 12 gynoecium with known regulators of flower and ovule development, such as AGAMOUS, SEEDSTICK, and SEPATALA 3. Collectively, our findings define a previously unrecognized function of SHP2 in the regulation of auxin biosynthetic genes during gynoecium development and raise the possibility that the auxin produced under SHP2 regulation may contribute significantly to the valve margin establishment.

In response to the escalating threat of climate change and its detrimental impact on plants' productivity and thus on global food security, a new Action called RECROP (Reproductive Enhancement of CROP resilience to extreme climate CA22157) has emerged, supported by the European Cooperation in Science and Technology (COST). Comprising an exceptional consortium of agronomists, physiologists, geneticists, biologists and bioinformaticians from academia, private sector, public institutions and other relevant organisations. RECROP sets out to support and transform current efforts for improving crop resilience through innovative and holistic approaches. This collaborative effort aims to unlock the secrets of crop sensitivity to environmental stresses during plant reproduction and design solutions to enhance crop yields in a sustainable manner.

Key messageGPI anchor addition is important for JAGGER localization and in vivo function. Loss of correct GPI anchor addition in JAGGER, negatively affects its localization and function.In flowering plants, successful double fertilization requires the correct delivery of two sperm cells to the female gametophyte inside the ovule. The delivery of a single pair of sperm cells is achieved by the entrance of a single pollen tube into one female gametophyte. To prevent polyspermy, Arabidopsis ovules avoid the attraction of multiple pollen tubes to one ovule–polytubey block. In Arabidopsisjagger mutants, a significant number of ovules attract more than one pollen tube to an ovule due to an impairment in synergid degeneration. JAGGER encodes a putative arabinogalactan protein which is predicted to be anchored to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Here, we show that JAGGER fused to citrine yellow fluorescent protein (JAGGER-cYFP) is functional and localizes mostly to the periphery of ovule integuments and transmitting tract cells. We further investigated the importance of GPI-anchor addition domains for JAGGER localization and function. Different JAGGER proteins with deletions in predicted ω-site regions and GPI attachment signal domain, expected to compromise the addition of the GPI anchor, led to disruption of JAGGER localization in the cell periphery. All JAGGER proteins with disrupted localization were also not able to rescue the polytubey phenotype, pointing to the importance of GPI-anchor addition to in vivo function of the JAGGER protein.

Presented here are model Yang cycle, ethylene biosynthesis and signaling pathways in Cannabis sativa. C. sativa floral transcriptomes were used to predict putative ethylene-related genes involved in sexual plasticity in the species. Sexual plasticity is a phenomenon, wherein organisms possess the ability to alter their phenotypic sex in response to environmental and physiological stimuli, without modifying their sex chromosomes. Cannabis sativa L., a medically valuable plant species, exhibits sexual plasticity when subjected to specific chemicals that influence ethylene biosynthesis and signaling. Nevertheless, the precise contribution of ethylene-related genes (ERGs) to sexual plasticity in cannabis remains unexplored. The current study employed Arabidopsis thaliana L. as a model organism to conduct gene orthology analysis and reconstruct the Yang Cycle, ethylene biosynthesis, and ethylene signaling pathways in C. sativa. Additionally, two transcriptomic datasets comprising male, female, and chemically induced male flowers were examined to identify expression patterns in ERGs associated with sexual determination and sexual plasticity. These ERGs involved in sexual plasticity were categorized into two distinct expression patterns: floral organ concordant (FOC) and unique (uERG). Furthermore, a third expression pattern, termed karyotype concordant (KC) expression, was proposed, which plays a role in sex determination. The study revealed that CsERGs associated with sexual plasticity are dispersed throughout the genome and are not limited to the sex chromosomes, indicating a widespread regulation of sexual plasticity in C. sativa.

Key messageContrasting morphologies in Disocactus are the result of differential development of the vegetative and floral tissue where intercalary growth is involved, resulting in a complex structure, the floral axis.Species from the Cactaceae bear adaptations related with their growth in environments under hydric stress. These adaptations have translated into the reduction and modification of various structures such as leaves, stems, lateral branches, roots and the structuring of flowers in a so-called flower-shoot. While cacti flowers and fruits have a consistent structure with showy hermaphrodite or unisexual flowers that produce a fruit called cactidium, the developmental dynamics of vegetative and reproductive tissues comprising the reproductive unit have only been inferred through the analysis of pre-anthetic buds. Here we present a comparative analysis of two developmental series covering the early stages of flower formation and organ differentiation in Disocactus speciosus and Disocactus eichlamii, which have contrasting floral morphologies. We observe that within the areole, a shoot apical meristem commences to grow upward, producing lateral leaves with a spiral arrangement, rapidly transitioning to a floral meristem. The floral meristem produces tepal primordia and a staminal ring meristem from which numerous or few stamens develop in a centrifugal manner in D. speciosus and D. eichlamii, respectively. Also, the inferior ovary derives from the floral meristem flattening and an upward growth of the surrounding tissue of the underlying stem, producing the pericarpel. This structure is novel to cacti and lacks a clear anatomical delimitation with the carpel wall. Here, we present a first study that documents the early processes taking place during initial meristem determination related to pericarpel development and early floral organ formation in cacti until the establishment of mature floral organs.

Plant architecture is an important feature for agronomic performance in crops. In maize, which is a monoecious plant, separation of floral organs to produce specific gametes has been studied from different perspectives including genetic, biochemical and physiological. Maize mutants affected in floral organ development have been key to identifying genes, hormones and other factors like miRNAs important for sex determination. In this review, we describe floral organ formation in maize, representative mutants and genes identified with a function in establishing sexual identity either classified as feminizing or masculinizing, and its relationship with hormones associated with sexual organ identity as jasmonic acid, brassinosteroid and gibberellin. Finally, we discuss the challenges and scopes of future research in maize sex determination.

The pollen germination rate decreases under various abiotic stresses, such as high-temperature stress, and it is one of the causes of inhibition of plant reproduction. Thus, measuring pollen germination rate is vital for understanding the reproductive ability of plants. However, measuring the pollen germination rate requires much labor when counting pollen. Therefore, we used the Yolov5 machine learning package in order to perform transfer learning and constructed a model that can detect germinated and non-germinated pollen separately. Pollen images of the chili pepper, Capsicum annuum, were used to create this model. Using images with a width of 640 pixels for training constructed a more accurate model than using images with a width of 320 pixels. This model could estimate the pollen germination rate of the F2 population of C. chinense previously studied with high accuracy. In addition, significantly associated gene regions previously detected in genome-wide association studies in this F2 population could again be detected using the pollen germination rate predicted by this model as a trait. Moreover, the model detected rose, tomato, radish, and strawberry pollen grains with similar accuracy to chili pepper. The pollen germination rate could be estimated even for plants other than chili pepper, probably because pollen images were similar among different plant species. We obtained a model that can identify genes related to pollen germination rate through genetic analyses in many plants.

At the heart of meiosis is crossover recombination, i.e., reciprocal exchange of chromosome fragments between parental genomes. Surprisingly, in most eukaryotes, including plants, several recombination pathways that can result in crossover event operate in parallel during meiosis. These pathways emerged independently in the course of evolution and perform separate functions, which directly translate into their roles in meiosis. The formation of one crossover per chromosome pair is required for proper chromosome segregation. This “obligate” crossover is ensured by the major crossover pathway in plants, and in many other eukaryotes, known as the ZMM pathway. The secondary pathways play important roles also in somatic cells and function mainly as repair mechanisms for DNA double-strand breaks (DSBs) not used for crossover formation. One of the consequences of the functional differences between ZMM and other DSB repair pathways is their distinct sensitivities to polymorphisms between homologous chromosomes. From a population genetics perspective, these differences may affect the maintenance of genetic variability. This might be of special importance when considering that a significant portion of plants uses inbreeding as a predominant reproductive strategy, which results in loss of interhomolog polymorphism. While we are still far from fully understanding the relationship between meiotic recombination pathways and genetic variation in populations, recent studies of crossovers in plants offer a new perspective.

Pistil AGPs display dynamic localization patterns in response to fertilization in tomato. SlyFLA9 (Solyc07g065540.1) is a chimeric Fasciclin-like AGP with enriched expression in the ovary, suggesting a potential function during pollen-pistil interaction. During fertilization, the male gametes are delivered by pollen tubes to receptive ovules, deeply embedded in the sporophytic tissues of the pistil. Arabinogalactan glycoproteins (AGPs) are a diverse family of highly glycosylated, secreted proteins which have been widely implicated in plant reproduction, particularly within the pistil. Though tomato (Solanum lycopersicum) is an important crop requiring successful fertilization for production, the molecular basis of this event remains understudied. Here we explore the spatiotemporal localization of AGPs in the mature tomato pistil before and after fertilization. Using histological techniques to detect AGP sugar moieties, we found that accumulation of AGPs correlated with the maturation of the stigma and we identified an AGP subpopulation restricted to the micropyle that was no longer visible upon fertilization. To identify candidate pistil AGP genes, we used an RNA-sequencing approach to catalog gene expression in functionally distinct subsections of the mature tomato pistil (the stigma, apical and basal style and ovary) as well as pollen and pollen tubes. Of 161 predicted AGP and AGP-like proteins encoded in the tomato genome, we identified four genes with specifically enriched expression in reproductive tissues. We further validated expression of two of these, a Fasciclin-like AGP (SlyFLA9, Solyc07g065540.1) and a novel hybrid AGP (SlyHAE, Solyc09g075580.1). Using in situ hybridization, we also found SlyFLA9 was expressed in the integuments of the ovule and the pericarp. Additionally, differential expression analyses of the pistil transcriptome revealed previously unreported genes with enriched expression in each subsection of the mature pistil, setting the foundation for future functional studies.