The MAP3K-Coding QUI-GON JINN (QGJ) Gene Is Essential to the Formation of Unreduced Embryo Sacs in Paspalum (original) (raw)
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Advances in Cloning and Expression of Apomixis-Specific Genes in Flowering Plants
Floriculture, Ornamental and Plant Biotechnology: Advances and Topical Issues Vol. I, 2006
Up to megasporogenesis, there is no difference between sexual and apomictic plants of Panicum maximum and Paspalum notatum. The most important, notable difference in both is that while the formed megaspore does not divide, and becomes degenerated, aposporous initial cell (AIC) derived from nucellar tissue appears and divides into 4 nucleate embryo sacs containing one egg, two synergids and one polar nucleus in P. maximum, and one egg, one synergid and two polar nuclei in P. notatum. A novel classification method, based on ovary length, for sampling different developmental stages of embryo sac formation in obligate sexual and facultatively apomictic genotypes of P. maximum has been employed to make a cDNA library and to isolate an AIC stage-specific cDNA clone, probably representing a full-length gene. The A2-134 cDNA, designed ASG-1 (apomixis-specific gene), was found to be expressed in flower buds of the apomictic but not of the sexual accession. The cDNA (1,177bp) codes for a protein of 305 amino acids with a molecular mass of 34.2 kDa. The in situ hybridization-analysis revealed that ASG-1 is not expressed in the ovule before and during megasporogenesis in both of P. maximum and P. notatum. With the appearance of AIC in the ovule of the apomictic type, ASG-1 expression is strong and specific to AIC and continues through different stages of the AIC-derived embryo sac development, but not in the sexual type. This indicates that the gene may play a role in this developmental process. In a heterologous system, using P. notatum, identical results were obtained.
Journal of Experimental Botany, 2010
Apomixis is defined as clonal reproduction by seed. A comparative transcriptomic analysis was undertaken between apomictic and sexual genotypes of Paspalum simplex Morong to identify apomixis-related polymorphisms at the level of mRNA. cDNA-AFLP (amplified fragment length polymorphism) profiling of apomictic and sexual flowers at several stages of development yielded 202 amplicons that showed several kinds of expression specificities. Among these, the large majority consisted of amplicons that were present only in specific stages of development of the apomictic flowers. Ten percent of polymorphic amplicons were present with almost identical intensity in all stages of the apomictic flowers and never in the sexual flowers. Reverse transcription-PCR (RT-PCR) and Southern analyses of these amplicons showed that they belong to constitutively expressed alleles that are specifically present on the apomixis-controlling locus of P. simplex. The most frequent biological functions inferred from the sequence homology of the apomixis-linked alleles were related to signal transduction and nucleic acid/protein-binding activities. Most of these apomixis-linked alleles showed nonsense and frameshift mutations, revealing their probable pseudogene nature. None of the amplicons that were present only in specific stages of development of the apomictic flowers co-segregated with apomixis, indicating they did not originate from additional apomictic alleles but more probably from differential regulation of the same allele in apomictic and sexual flowers. The molecular functions inferred from sequence analysis of these latter amplicons were related to seed storage protein and regulatory genes of various types. The results are discussed regarding the possible role in apomictic reproduction of the differentially expressed genes in relation to their specificity of expression and inferred molecular functions.
Plants
The capacity for apomixis in Paspalum notatum is controlled by a single-dominant genomic region, which shows strong synteny to a portion of rice chromosome 12 long arm. The locus LOC_Os12g40890, encoding the Auxin/Indole-3-Acetic Acid (Aux/IAA) family member OsIAA30, is located in this rice genomic segment. The objectives of this work were to identify transcripts coding for Aux/IAA proteins expressed in reproductive tissues of P. notatum, detect the OsIAA30 putative ortholog and analyze its temporal and spatial expression pattern in reproductive organs of sexual and apomictic plants. Thirty-three transcripts coding for AUX/IAA proteins were identified. Predicted protein alignment and phylogenetic analysis detected a highly similar sequence to OsIAA30 (named as PnIAA30) present in both sexual and apomictic samples. The expression assays of PnIAA30 showed a significant down-regulation in apomictic spikelets compared to sexual ones at the stages of anthesis and post-anthesis, represent...
Organogenesis in plants: the molecular and genetic control of ovule development
Trends in plant science, 1998
T he ovule is the principal female reproductive organ in higher plants. In angiosperms the ovule is located within the gynoecium, which consists of one, or several, usually fused, carpels. Before fertilization, the mature ovule consists of a haploid multicellular embryo sac or female gametophyte, surrounded by diploid or sporophytic tissue ). The egg cell is one of usually seven cells of the embryo sac. Following fertilization the ovule develops into the seed carrying the embryo.
Frontiers in Plant Science, 2019
Aposporous apomictic plants form clonal maternal seeds by inducing the emergence of non-reduced (2n) embryo sacs in the ovule nucellus and the development of embryos by parthenogenesis. In previous work, we reported a plant-specific TRIMETHYLGUANOSINE SYNTHASE 1 (TGS1) gene (PN_TGS1-like) showing expression levels positively correlated with sexuality rates in facultative apomictic Paspalum notatum. PN_ TGS1-like displayed contrasting in situ hybridization patterns in apomictic and sexual plant ovules from premeiosis to anthesis. Here we transformed sexual P. notatum with a TGS1-like antisense construction under a constitutive promoter, in order to produce lines with reduced transcript representation. Antisense plants developed prominent trichomes on the adaxial leaf surface, a trait absent from control genotypes. Reproductive development analysis revealed occasional formation of twin ovules. While control individuals typically displayed a single meiotic embryo sac per ovule, antisense lines showed 12.93–15.79% of ovules bearing extra nuclei, which can be assigned to aposporous-like embryo sacs (AES-like) or, alternatively, to gametophytes with a misguided cell fate development. Moreover, around 8.42–9.52% of ovules showed what looked like a combination of meiotic and aposporous-like sacs. Besides, 32.5% of ovules at early developmental stages displayed nucellar cells with prominent nuclei resembling apospory initials (AIs), which surrounded the megaspore mother cell (MMC) or the MMC-derived meiotic products. Two or more concurrent meiosis events were never detected, which suggest a non-reduced nature for the extra nuclei observed in the mature ovules, unless they were generated by proliferation and misguided differentiation of the legitimate meiotic products. The antisense lines produced a similar amount of viable even-sized pollen with respect to control genotypes, and formed an equivalent full seed set (∼9% of total seeds) after self-pollination. Flow cytometry analyses of caryopses derived from antisense lines revealed that all full seeds had originated from meiotic embryo sacs (i.e. by sexuality). A reduction of 25.55% in the germination percentage was detected when comparing antisense lines with controls. Our results indicate that PN_ TGS1-like influences ovule, gametophyte and possibly embryo development.
Meiotic and apomictic reproductive pathways develop simultaneously in facultative aposporous species, and compete to form a seed as a final goal. This developmental competition was evaluated in tetraploid genotypes of Paspalum malacophyllum in order to understand the low level of sexuality in facultative apomictic populations. Cyto-embryology on ovules, flow cytometry on seeds and progeny tests by DNA fingerprinting were used to measure the relative incidence of each meiotic or apomictic pathway along four different stages of the plant’s life cycle, namely the beginning and end of gametogenesis, seed formation and adult offspring. A high variation in the frequencies of sexual and apomictic pathways occurred at the first two stages. A trend of radical decline in realized sexuality was then observed. Sexual and apomictic seeds were produced, but the efficiency of the sexual pathway dropped drastically, and exclusively clonal offspring remained. Both reproductive pathways are unstable at the beginning of development, and only the apomictic one remains functional. Key factors reducing sexuality are the faster growth and parthenogenetic development in the aposporous pathway, and an (epi)genetically negative background related to the extensive gene de-regulation pattern responsible for apomixis. The effects of inbreeding depression during post-fertilization development may further decrease the frequency of effective sexuality.
Apomixis is desirable in agriculture as a reproductive strategy for cloning plants by seeds. Because embryos derive from the parthenogenic development of apomeiotic egg cells, apomixis excludes fertilization in addition to meiotic segregation and recombination, resulting in offspring that are exact replicas of the parent. Introgression of apomixis from wild relatives to crop species and transformation of sexual genotypes into apomictically reproducing ones are long-held goals of plant breeding. In fact, it is generally accepted that the introduction of apomixis into agronomically important crops will have revolutionary implications for agriculture. This review deals with the current genetic and molecular findings that have been collected from model species to elucidate the mechanisms of apomeiosis, parthenogenesis and apomixis as a whole. Our goal is to critically determine whether biotechnology can combine key genes known to control the expression of the processes miming the main components of apomixis in plants. Two natural apomicts, as the eudicot Hypericum perforatum L. (St. John's wort) and the monocot Paspalum spp. (crowngrass), and the sexual model species Arabidopsis thaliana are ideally suited for such investigations at the genomic and biotechnological levels. Some novel views and original concepts have been faced on this review, including (i) the parallel between Y-chromosome and apomixis-bearing chromosome (e.g., comparative genomic analyses revealed common features as repression of recombination events, accumulation of transposable elements and degeneration of genes) from the most primitive (Hypericum-type) to the most advanced (Paspalum-type) in evolutionary terms, and (ii) the link between apomixis and gene-specific silencing mechanisms (i.e., likely based on chromatin remodelling factors), with merging lines of evidence regarding the role of auxin in cell fate specification of embryo sac and egg cell development in Arabidopsis. The production of engineered plants exhibiting apomictic-like phenotypes is critically reviewed and discussed.
SERK and APOSTART. Candidate Genes for Apomixis in Poa pratensis
PLANT PHYSIOLOGY, 2005
Seed production generally requires the mating of opposite sex gametes. Apomixis, an asexual mode of reproduction, avoids both meiotic reduction and egg fertilization. The essential feature of apomixis is that an embryo is formed autonomously by parthenogenesis from an unreduced egg of an embryo sac generated through apomeiosis. If apomixis were well understood and harnessed, it could be exploited to indefinitely propagate superior hybrids or specific genotypes bearing complex gene sets. A more profound knowledge of the mechanisms that regulate reproductive events would contribute fundamentally to understanding the genetic control of the apomictic pathway. In Poa pratensis, we isolated and characterized two genes, PpSERK (SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE) and APOSTART. These full-length genes were recovered by rapid amplification of cDNA ends and their temporal and spatial expression patterns were assessed by reverse transcriptionpolymerase chain reaction and in situ hybridization, respectively. The expression of PpSERK and APOSTART differed in apomictic and sexual genotypes. Their putative role in cell-signaling transduction cascades and trafficking events required during sporogenesis, gametogenesis, and embryogenesis in plants is reported and discussed. We propose that, in nucellar cells of apomictic genotypes, PpSERK is the switch that channels embryo sac development and that it may also redirect signaling gene products to compartments other than their typical ones. The involvement of APOSTART in meiosis and programmed cell death is also discussed.
Expression of lorelei-like genes in aposporous and sexual Paspalum notatum plants
Plant Molecular Biology, 2011
Gametophytic apomictic plants form nonreduced embryo sacs that generate clonal embryos by parthenogenesis, in the absence of both meiosis and eggcell fertilization. Here we report the sequence and expression analysis of a lorelei-like Paspalum notatum gene, n20gap-1, which encodes a GPI-anchored protein previously associated with apomixis in this species. Phylogeny trees showed that n20gap-1 was evolutionary related to the Arabidopsis thaliana lorelei genes At4g26466 and At5g56170. The lorelei At4g26466 disruption was shown to be detrimental to sperm cell release in arabidopsis. RFLP (Restriction Fragment Length Polymorphism) analysis revealed the occurrence of several homologous sequences in the Paspalum notatum genome, exhibiting polymorphisms genetically linked to apomixis. Real-time PCR showed that lorelei-family genes present a minor activity peak at pre-meiosis and a major one at anthesis. The apomictic genotype analyzed showed a significantly increased activity at pre-meiosis, post-meiosis and anthesis with respect to a sexual genotype. In situ hybridization assays revealed expression in integuments, nucellus and the egg-cell apparatus. Several n20gap-1 alleles differing mainly at the 3 0 UTR sequence were identified. Allelespecific real-time PCR experiments showed that allele 28 was significantly induced in reproductive tissues of the apomictic genotype with respect to the sexual genotype at anthesis. Our results indicate that P. notatum lorelei-like genes are differentially expressed in representative sexual (Q4188) and apomictic (Q4117) genotypes, and might play a role in the final stages of the apomixis developmental cascade. However, the association of n20gap-1 expression with the trait should be confirmed in significant number of sexual and apomictic genotypes.
Frontiers in plant science, 2018
Apomixis is a clonal mode of reproduction via seeds, which results from the failure of meiosis and fertilization in the sexual female reproductive pathway. In previous transcriptomic surveys, we identified a mitogen-activated protein kinase kinase kinase (N46) displaying differential representation in florets of sexual and apomictic genotypes. Here, we retrieved and characterized the N46 full cDNA sequence from sexual and apomictic floral transcriptomes. Phylogenetic analyses showed that N46 was a member of the family, which was re-named (). Differential expression in florets of sexual and apomictic plants was confirmed by qPCR. hybridization experiments revealed expression in the nucellus of aposporous plants' ovules, which was absent in sexual plants. RNAi inhibition of expression in two apomictic genotypes resulted in significantly reduced rates of aposporous embryo sac formation, with respect to the level detected in wild type aposporous plants and transformation controls. T...