Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • br Introduction In most of the angiosperms sexual

    2021-04-10


    Introduction In most of the angiosperms, sexual reproduction requires a process called double fertilization where the specialized cell division called meiosis produces haploid gametes combine to form diploid (2n) embryo. In Vanoxerine to this, apomixis, naturally occurs in at least 400 plant families (Carman, 1997), represents an exception since the embryo formation occurs without fertilization of the egg (Koltunow, 1993). Previous studies suggest that three elements are commonly observed in apomicts; the generation of a cell capable of forming an embryo without prior meiosis (apomeiosis); the spontaneous, fertilization-independent development of the embryo (parthenogenesis); and the capacity to either produce endosperm autonomously or to use a pseudogamous endosperm derived from fertilization (Koltunow, 1993, Bicknell and Koltunow, 2004, Vielle-Calzada et al., 1996). It has been already proposed that apomixis has a potential to change hybrid seed technology by providing a new tool to maintain hybrid vigour in plant breeding since the progeny of apomictic plants is genetically identical to the mother plant (Grimanelli et al., 2001, Koltunow et al., 2001). Although, the molecular mechanisms underlying apomixis are not known, studies suggest that apomixis may emerge from the sexual system deregulated by epigenetic modifications (Carman, 1997, Curtis and Grossniklaus, 2008, Grimanelli, 2012, Grimanelli et al., 2003, Koltunow and Grossniklaus, 2003). These studies include mutations in various genes involves epigenetic pathways such as ARGONAUTE 9, RNA POLYMERASE 6 and SUPPRESSOR OF GENE SILENCING3 in Arabidopsis and DNA METHYLTRANSFERASES (DMT102 and DMT103) and AGO104 in maize showed apomixis-like phenotypes (Garcia-Aguilar et al., 2010, Olmedo-Monfil et al., 2010, Singh et al., 2011). The dmt102 and dmt103 mutant lines of maize showed apomixis like phenotypes such as the production of unreduced gametes and formation of multiple embryo sacs in the ovule and this may suggest that DNA Methyltransferase genes may have a role in apomixis (Garcia-Aguilar et al., 2010). Therefore epigenetic regulation in natural apomict species should be investigated further. In the genus Boechera (Brassicaceae) both sexual and apomict species are available and this makes Boechera attractive model species to study apomixis since they are close relatives of Arabidopsis thaliana (Dobes et al., 2006, Schranz et al., 2005, Schranz et al., 2006, Sharbel et al., 2010a, Sharbel et al., 2010b, Sharbel et al., 2004). In apomictic Boechera species Taraxacum type diplospory are observed and common with many apomicts, endosperm development require fertilization by a sperm (Schranz et al., 2006, Naumova et al., 2001). Boechera divaricarpa is known as an interspecific hybrid species emerging between sexual B. stricta and B. holboellii or a closely related species (Dobes et al., 2004, Koch et al., 2003). Although diploid apomixis is an extremely rare condition in plants (Voigt-Zielinski et al., 2012), previously, both diploid and triploid apomict B. divaricarpa lineages have been reported (Schranz et al., 2005). DNA methylation is one of the most important epigenetic regulations in plants and DNMTs are responsible for the symmetric (CpG and CpNpG) and asymmetric (CpNpN) cytosine methylations in plant genome (Cao and Jacobsen, 2002a, Cao and Jacobsen, 2002b). There are three different DNMT genes called METHYLTRANSFERASE1 (MET1), CHROMOMETHYLASE 3 (CMT3) and DOMAINS REARRANGED METHYLTRANSFERASE 1/2 (DRM1/2), are encoded in A. thaliana genome (Cao and Jacobsen, 2002a, Cao and Jacobsen, 2002b, Bartee et al., 2001, Finnegan et al., 1996, Finnegan et al., 2000, Goll and Bestor, 2005, Lindroth et al., 2001). MET1 is responsible for CpG methylation and has an important role in silencing the transposons and repeats elements and also maintains marks on some imprinted genes (Finnegan et al., 2000, Kankel et al., 2003, Kinoshita et al., 1999, Saze et al., 2003, Vielle-Calzada et al., 1999, Xiao et al., 2003). CMT3 is a plant specific protein and maintains methylation in de novo sequences and also helps transposon silencing (Cao and Jacobsen, 2002a, Bartee et al., 2001, Lindroth et al., 2001, Chan et al., 2004, Kim and Zilberman, 2014, Miura et al., 2001). DRM1 and DRM2 require siRNA targeting to methylate at nonsymetrical CHH sequences and responsible for de novo methylation (Cao and Jacobsen, 2002b, Finnegan and Kovac, 2000).