Plant Reproduction最新文献

Key message

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.

Abstract

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 message

Antagonistic expression of Flowering locus T proteins and the ageing pathway via miRNAs and sugar metabolism regulate the initiation of flowering in A. tequilana.

Abstract

Flowering in commercial plantations of Agave tequilana signals that plants are ready to harvest for tequila production. However, time of flowering is often unpredictable and a detailed understanding of the process would be beneficial in the field, for breeding and for the development of future research. This report describes the functional analysis of A. tequilana FLOWERING LOCUS T (FT) genes by heterologous expression in A. thaliana and in situ hybridization in agave plants. The gene structures of the Agave tequilana FT family are also described and putative regulatory promoter elements were identified. Most Agave species have monocarpic, perennial life cycles that can last over 25 years during which plants do not respond to the normal environmental signals which induce flowering, suggesting that the ageing pathway as described in Arabidopsis may play an important role in determining flowering time in these species. Elements of this pathway were analyzed and in silico data is presented that supports the regulation of SQUAMOSA PROMOTER BINDING LIKE proteins (SPL), APETALA2 (AP2) proteins and members of Plant Glycoside Hydrolase Family 32 (PGHF32) by interactions with miRNAs 156, 172 and 164 during the initiation of flowering in A. tequilana.

The cell cycle controls division and proliferation of all eukaryotic cells and is tightly regulated at multiple checkpoints by complexes of core cell cycle proteins. Due to the difficulty in accessing female gametes and zygotes of flowering plants, little is known about the molecular mechanisms underlying embryogenesis initiation despite the crucial importance of this process for seed crops. In this study, we reveal three levels of factors involved in rice zygotic cell cycle control and characterize their functions and regulation. Protein-protein interaction studies, including within zygote cells, and in vitro biochemical analyses delineate a model of the zygotic cell cycle core complex for rice. In this model, CDKB1, a major regulator of plant mitosis, is a cyclin (CYCD5)-dependent kinase; its activity is coordinately inhibited by two cell cycle inhibitors, KRP4 and KRP5; and both KRPs are regulated via F-box protein 3 (FB3)-mediated proteolysis. Supporting their critical roles in controlling the rice zygotic cell cycle, mutations in KRP4, KRP5 and FB3 result in the compromised function of sperm cells and abnormal organization of female germ units, embryo and endosperm, thus significantly reducing seed-set rate. This work helps reveal regulatory mechanisms controlling the zygotic cell cycle toward seed formation in angiosperms.

Coat protein I (COPI) and Coat protein II (COPII) coated vesicles mediate protein transport in the early secretory pathway. Although several components of COPII vesicles have been shown to have an essential role in Arabidopsis gametogenesis, the function of COPI components in gametogenesis has not been studied in detail. COPI consists of a heptameric complex made of α, β, β', γ, δ, ɛ, and ζ-COP subunits and most subunits have several isoforms in Arabidopsis. We have found that two isoforms of the β'-COP subunit, β'1-COP and β'2-COP, are required for female and male gametophyte development. Reciprocal crosses between wild type plants and plants heterozygous for T-DNA insertions in β'1-COP and β'2-COP showed that β'1β'2-cop gametophytes are not transmitted.

Key message: Functional loss of Arabidopsis Sar1b with that of either Sar1a or Sar1c inhibits mitosis of functional megaspores, leading to defective embryo sac formation and reduced fertility. Vesicular trafficking among diverse endomembrane compartments is critical for eukaryotic cells. Anterograde trafficking from endoplasmic reticulum (ER) to the Golgi apparatus is mediated by coat protein complex II (COPII) vesicles. Among five cytosolic components of COPII, secretion-associated Ras-related GTPase 1 (Sar1) mediates the assembly and disassembly of the COPII coat. Five genes in Arabidopsis encode Sar1 isoforms, whose different cargo specificities and redundancy were both reported. We show here that Arabidopsis Sar1a, Sar1b, and Sar1c mediate the development of female gametophytes (FGs), in which Sar1b plays a major role, whereas Sar1a and Sar1c play a minor role. We determined that female transmission of sar1a;sar1b or sar1c;sar1b was significantly reduced due to defective mitosis of functional megaspores. Half of ovules in sar1a;sar1b/+ or sar1c;sar1b/+ plants failed to attract pollen tubes, leading to fertilization failure. The homozygous sar1a;sar1b or sar1c;sar1b double mutant was obtained by introducing either UBQ10:GFP-Sar1b or UBQ10:GFP-Sar1c, supporting their redundant function in FG development.

Key message: Genome-wide identification of C2H2-ZF gene family in the poly- and mono-embryonic citrus species and validation of the positive role of CsZFP7 in sporophytic apomixis. The C2H2 zinc finger (C2H2-ZF) gene family is involved in plant vegetative and reproductive development. Although a large number of C2H2 zinc-finger proteins (C2H2-ZFPs) have been well characterized in some horticultural plants, little is known about the C2H2-ZFPs and their function in citrus. In this work, we performed a genome-wide sequence analysis and identified 97 and 101 putative C2H2-ZF gene family members in the genomes of sweet orange (C. sinensis, poly-embryonic) and pummelo (C. grandis, mono-embryonic), respectively. Phylogenetic analysis categorized citrus C2H2-ZF gene family into four clades, and their possible functions were inferred. According to the numerous regulatory elements on promoter, citrus C2H2-ZFPs can be divided into five different regulatory function types that indicate functional differentiation. RNA-seq data revealed 20 differentially expressed C2H2-ZF genes between poly-embryonic and mono-embryonic ovules at two stages of citrus nucellar embryogenesis, among them CsZFP52 specifically expressed in mono-embryonic pummelo ovules, while CsZFP7, 37, 44, 45, 67 and 68 specifically expressed in poly-embryonic sweet orange ovules. RT-qPCR further validated that CsZFP7 specifically expressed at higher levels in poly-embryonic ovules, and down-regulation of CsZFP7 in the poly-embryonic mini citrus (Fortunella hindsii) increased rate of mono-embryonic seeds compared with the wild type, indicating the regulatory potential of CsZFP7 in nucellar embryogenesis of citrus. This work provided a comprehensive analysis of C2H2-ZF gene family in citrus, including genome organization and gene structure, phylogenetic relationships, gene duplications, possible cis-elements on promoter regions and expression profiles, especially in the poly- and mono-embryogenic ovules, and suggested that CsZFP7 is involved in nucellar embryogenesis.

Key message: Our results indicate the existence of interploidy gene flow in Cystopteris fragilis, resulting in sexual triploid and diploid gametophytes from pentaploid parents. Similar evolutionary dynamics might operate in other fern complexes and need further investigation. Polyploidization and hybridization are a key evolutionary processes in ferns. Here, we outline an interploidy gene flow pathway operating in the polyploid Cystopteris fragilis complex. The conditions necessary for the existence of this pathway were tested. A total of 365 C. fragilis individuals were collected covering representatives of all three predominant ploidy levels (tetraploid, pentaploid, and hexaploid), cultivated, had their ploidy level estimated by flow cytometry, and their spores collected. The spores, as well as gametophytes and sporophytes established from them, were analysed by flow cytometry. Spore abortion rate was also estimated. In tetraploids, we observed the formation of unreduced (tetraploid) spores (ca 2%). Collected pentaploid individuals indicate ongoing hybridization between ploidy levels. Pentaploids formed up to 52% viable spores, ca 79% of them reduced, i.e. diploid and triploid. Reduced spores formed viable gametophytes, and, in the case of triploids, filial hexaploid sporophytes, showing evidence of sexual reproduction. Some tetraploid sporophytes reproduce apomictically (based on uniform ploidy of their metagenesis up to filial sporophytes). Triploid and diploid gametophytes from pentaploid parents are able to mate among themselves, or with "normal" reduced gametophytes from the sexual tetraploid sporophytes (the dominant ploidy level in the sporophytes in this populations), to produce tetraploid, pentaploid, and hexaploid sporophytes, allowing for geneflow from the pentaploids to both the tetraploid and hexaploid populations. Similar evolutionary dynamics might operate in other fern complexes and need further investigation.

Key message: Asymmetric meiosis leading to the release of pollen grains as pseudomonads is a synapomorphy in Cyperaceae, but differences in microspore development are relevant in the family's evolutionary history. Cyperaceae members present atypical microsporogenesis, in which one meiotic product is functional while the other three degenerate, culminating in pseudomonad pollen formation. Differences during development, such as pseudomonad shape and degenerative microspore positioning, are seen throughout the family, but no phylogenetic interpretation has been made regarding these variances thus far. In this study, we analyzed the early- and late-diverging sedge genera Hypolytrum and Eleocharis, respectively, while comparing them to data available in the literature and conducting an ancestral character reconstruction for pseudomonad traits. Light microscopy results show that pseudomonad development in Hypolytrum is homologous to several other sedge genera, presenting apical degenerative microspores. However, pseudomonads are round and centrally arranged in the anther locule in this case, which consists of a pleisiomorphic trait for the family. The basal positioning of degenerative microspores is restricted to Rhynchospora, consisting of an apomorphic trait for this genus. Despite these differences, ultrastructural analysis of Eleocharis pseudomonad revealed shared features with other genera studied, which include variations in chromatin condensation and cytoplasmic turnover in functional cells. These common features seem related to the different cellular fates seen during microspore development and further corroborate the synapomorphic status of pseudomonads in sedges.

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.

Key message: The main features of generative cell morphogenesis, formation of a cytoplasmic projection and elongation of the GC body, operate through independent genetic pathways. Male gametogenesis in developing angiosperm pollen involves distinctive changes in cell morphogenesis. Re-shaping and elongation of the generative cell (GC) are linked to the formation of a GC cytoplasmic projection connected to the vegetative cell nucleus. Although genetic control of GC morphogenesis is unknown, we suspected the involvement of the germline-specific MYB transcription factor DUO POLLEN1 (DUO1). We used light and fluorescence microscopy to examine male germline development in pollen of wild-type Arabidopsis and in four allelic duo1 mutants expressing introduced cell markers. Our analysis shows that the undivided GC in duo1 pollen forms a cytoplasmic projection, but the cell body fails to elongate. In contrast GCs of cyclin-dependent kinase function mutants, which fail to divide like duo1 mutants, achieve normal morphogenesis. We conclude that DUO1 has an essential role in the elongation of the GC, but DUO1-independent pathways control the development of the GC cytoplasmic projection. The two main features of GC morphogenesis therefore operate through independently regulated genetic pathways.