Flowering plant reproduction is characterized by double fertilization, in which two diminutive brother sperm cells initiate embryo and endosperm. The role of the male gamete, although studied structurally for over a century at various levels, is still being explored on a molecular and cellular level. The potential of the male to influence development has been historically underestimated and the reasons for this are obvious: limitations provided by maternal imprinting, the much greater cellular volume of female gametes and the general paucity of paternal effects. However, as more is known about molecular expression of chromatin-modifying proteins, ubiquitin pathway proteins and transcription factors in sperm cells, as well as their ability to achieve effect by intaglio expression, passing transcripts directly into translation, the role of the male is likely to expand. Much of the expression in the male germline that appears to be distinct from patterns of pollen vegetative cell expression may be the result of chromosomal level regulation of transcription.
"In P. zeylanica, which bears dimorphic sperm cells, similar transmission may occur; the dimorphic sperm cells of this plant are targeted to fuse specifically with either the egg or the central cell and display transcriptional profiles that appear to reflect the respective female cell with which the gamete will fuse (Gou et al., 2009). For example, the sperm cell type that normally fuses with the central cell contains numerous copies of isopentenyl transferase, a control enzyme for cytokinin synthase, which drives endosperm development, whereas the sperm cell that fuses with the egg has an embryo-like profile (Russell et al., 2010). Paternal transcripts have also been observed in tobacco zygotes using RT-PCR (Ning et al., 2006) and are selectively persistent after fertilization (Xin et al., 2011). "
[Show abstract][Hide abstract] ABSTRACT: Genomic assay of sperm cell RNA provides insight into functional control, modes of regulation, and contributions of male gametes to double fertilization. Sperm cells of rice (Oryza sativa) were isolated from field-grown, disease-free plants and RNA was processed for use with the full-genome Affymetrix microarray. Comparison with Gene Expression Omnibus (GEO) reference arrays confirmed expressionally distinct gene profiles. A total of 10,732 distinct gene sequences were detected in sperm cells, of which 1668 were not expressed in pollen or seedlings. Pathways enriched in male germ cells included ubiquitin-mediated pathways, pathways involved in chromatin modeling including histones, histone modification and nonhistone epigenetic modification, and pathways related to RNAi and gene silencing. Genome-wide expression patterns in angiosperm sperm cells indicate common and divergent themes in the male germline that appear to be largely self-regulating through highly up-regulated chromatin modification pathways. A core of highly conserved genes appear common to all sperm cells, but evidence is still emerging that another class of genes have diverged in expression between monocots and dicots since their divergence. Sperm cell transcripts present at fusion may be transmitted through plasmogamy during double fertilization to effect immediate post-fertilization expression of early embryo and (or) endosperm development.
New Phytologist 06/2012; 195(3):560-73. DOI:10.1111/j.1469-8137.2012.04199.x · 7.67 Impact Factor
"Recently, sperm cells were found to harbor a much more diverse transcriptome than anticipated, which can also influence the next sporophyte generation (Borges et al. 2008; Gou et al. 2009; Russell et al. 2010). Polarity establishment and maintenance in the microspore depends on cytoskeletal components, in particular microtubules, and is required for asymmetrical division, which initiates cellular differentiation. "
[Show abstract][Hide abstract] ABSTRACT: Plants have a complex life cycle in which diploid and haploid generations alternate: the diploid sporophyte produces the spores, while the haploid gametophytes form the gametes. In bryophytes and ferns, the dimorphic gametophytes are free-living, but their development has become dependent on the sporophyte in seed plants. This opens a multitude of opportunities for interactions and cross-talk between the two generations, many of which are discussed in this issue of Sexual Plant Reproduction. In angiosperms, gametophytes develop within the reproductive organs of the flower: the male gametophyte (pollen) within the anthers and the female gametophyte (embryo sac) within the ovule, which develops from the placental tissues of the carpel (Ma and Sundaresan 2010). The gametophytes in turn differentiate one pair of gametes each. During double fertilization, which initiates seed development, one sperm fuses with the central cell producing the endosperm, while the second fertilizes the egg to form the embryo and thus the next sporophyte generation. Although Theophrastus of Eresos (371‐287 BC), the ‘Father of Botany’, already recognized the existence of male and female plants (Negbi 1995), it took the offering of a prize by the Imperial Academy of Sciences in St. Peterburg, to experimentally prove that plants reproduce sexually just as animals do. By crossing Nicotiana rustica
Sexual Plant Reproduction 06/2011; 24(2):91-5. DOI:10.1007/s00497-011-0170-3 · 0.93 Impact Factor
"Our current knowledge of pollen development , although has expanded in the last decade ( McCormick 2004 ; Russell et al . 2010 ) is still very fragmentary and discrete . In the last decade , more and more emphasis has been placed on model systems such as Arabidopsis to understand the development of pollen grain and events involved in fertilization ."
[Show abstract][Hide abstract] ABSTRACT: Introduction of foreign genes and development of transgenic plants have become an integral part of crop improvement programmes in the last decade. However, most of the present day plant transformation protocols require long periods for development of transgenic plants and need skilled personnel. Development of alternate, simple and rapid transformation protocols for development of transgenic plants can overcome the constraints of in vitro culture, regeneration and associated problems. Pollen grains, due to their abundance and ease with which they can be handled are ideal targets for introduction of foreign genes into the germ line. However, progress in introduction of transgenes into pollen grains and their subsequent use in fertilization leading to development of transgenic plants are limited. With the recent progress made in understanding of pollen development along with reports of successful pollen-mediated transformation in important crop plants, it should be possible to extend this simple method of transformation to other crop plants. The review deals with development of pollen grains as a target for introduction of genes with special emphasis on recent developments.
Physiology and Molecular Biology of Plants 03/2011; 17(1):1-8. DOI:10.1007/s12298-010-0042-6
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