Harnessing the developmental potential of nucellar cells: barriers and opportunities

Ranganath, R. M.

doi:10.1016/j.tibtech.2004.08.010

Cited by 12 publications

(10 citation statements)

References 58 publications

(56 reference statements)

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“…Although the proposition for an epigenetic role have been put forward for the emergence of apomixis from the sexual pathway (regulation through epialleles, relaxation of genomic imprinting), its relevance remains largely unexplored , Koltunow and Grossniklaus, 2003, Ranganath, 2004. As discussed below, our observations lend support to epigenetics as a critical component in the biology of apomicts along two different lines: seed development and transgenerational propagation of apomixis.…”

Section: Discussionsupporting

confidence: 58%

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Leblanc¹,

Grimanelli²,

Hernandez-Rodriguez³

et al. 2009

Int. J. Dev. Biol.

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Apomixis in plants covers a variety of cloning systems through seeds of great potential for plant breeding. Among long-standing approaches for crop improvement is the attempt to exploit wild relatives as natural, vast reservoirs for novel genetic variation. With regard to apomixis, maize possesses an apomictic wild relative, Tripsacum, which we used to produce advanced maize-Tripsacum hybrid generations. However, introgression of apomixis in maize has failed so far. In order to understand the how's and why's, we undertook characterization of seed development and inheritance studies in these materials. We show that apomictic seeds suffer from epigenetic loads. Both seed tissues, the endosperm and the embryo, displayed developmental defects resulting from imbalanced parental genomic contributions and aberrant methylation patterns, respectively. Progeny characterization of several maize-Tripsacum hybrid generations allowed significant progress toward the unraveling of the genetics of apomixis. First, chromosome deletion mapping showed that expression of apomixis requires one single Tripsacum chromosome. However, inheritance studies revealed that female gametes inheriting this segment were unequivalent carriers depending on their origin: unreduced gametes transmit a functional segment, whereas progeny derived from reduced ones reproduced sexually. Finally, chromosomal or genomic dosage variation barely affected the apomictic phenotype suggesting no dependency for ploidy in these materials. We conclude that epigenetic information imposes constraints for apomictic seed development and seems pivotal for transgenerational propagation of apomixis. The nature of the triggering mechanisms remains unknown as-yet, but it certainly explains the modest success relative to the development of apomictic maize thus far.

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Section: Discussionsupporting

confidence: 58%

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Leblanc¹,

Grimanelli²,

Hernandez-Rodriguez³

et al. 2009

Int. J. Dev. Biol.

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“…In a few tree species, many embryos are produced by apomixis. For example, in Citrus up to 80 adventitious embryos can develop in the ovule (Ranganath 2004). For clonal propagation of difficult-to-propagate individuals it would be of interest if aposporous apomixis could be duplicated by experimental means.…”

Section: Apomixismentioning

confidence: 99%

“…Whether ovular cells follow the aposporous or diplosporous pathway depends largely on epigenetic determining factors, i.e., apomixis is probably controlled by epigenetic gene regulation rather than by mutant alleles (Ranganath 2004). Apomixis is a heritable trait that can be transferred to a next generation by conventional breeding and thus could serve to produce new genotypes that could be further propagated through clonal seed (Estrada-Luna et al 2002;Ranganath 2004). Whether genes involved in initiation of natural apomixis and meiosis could be ectopically expressed in tissues of recalcitrant individuals, thus inducing apomixis in these tissues, remains to be determined.…”

Section: Apomixismentioning

confidence: 99%

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Recalcitrance in clonal propagation, in particular of conifers

Bonga

Klimaszewska

Aderkas

2009

Plant Cell Tiss Organ Cult

172

136

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Despite major advances in forest biotechnology, clonal regeneration by somatic embryogenesis or organogenesis is still difficult for many woody species and is often limited to the use of juvenile explants. Adventitious regeneration of plants from gymnosperms older than zygotic embryos, and frequently even from highly immature zygotic embryos, is often difficult or has not yet been achieved. A number of experimental approaches that could eventually lead to overcoming recalcitrance are suggested in this review. When cloning trees of various ages, it is important to determine first which part of the individual contains the most responsive cells and at what time of the year these cells are in the most responsive state. This allows selection of the most useful explants. In hardwood trees and a few gymnosperms, responsive tissues are found in root or stump sprouts and in tissues near the site of meiosis at about the time that meiosis takes place. Another potentially active area is the shoot apex with most or all of its leaf or needle primordia removed. Apomixis is a natural form of clonal regeneration but occurs naturally in only one gymnosperm species. As the genetic mechanism of apomixis has been in part elucidated, the induction of apomixis by experimental means may soon be possible. The cytoplasm plays a major role in the expression or repression of nuclear genes that control embryogenesis. Expression of nuclear genes can be manipulated by nuclear transfer into de-nucleated cells (e.g., the cytoplasm of egg cells). Cytoplasmic control also plays a role in regeneration by androgenesis, asymmetric cell division and cell isolation. A short overview is presented of the genetic mechanisms involved in embryo initiation, maturation and germination and how manipulation of these mechanisms by genetic transformation could help in overcoming recalcitrance. It is expected that rapid development in the fields of research areas discussed in this review will over time eliminate the problem of recalcitrance in many instances where it is currently prevalent.

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“…The molecular mechanisms that underlie the developmental switch that directly transforms a somatic plant cell to an embryo are still elusive 9 . Several genes, such as WUSCHEL (WUS), SOMATIC EMBRYO RECEPTOR-LIKE KINASE 1 (SERK1), LEAFY COTYLEDON 1 (LEC1), LEC2 and BABY BOOM (BBM), can induce embryonic growth in plant somatic cells 10 , and Polycomb group proteins are also implicated in somatic embryogenesis 11 . However, it is uncertain whether these pathways for reprogramming of plant somatic cells towards embryogenesis are conserved among species.…”

mentioning

confidence: 99%

Developmental switches that hold the key to a revolution in crop biotechnology

Ranganath¹

2011

Nat Rev Genet

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Harnessing the developmental potential of nucellar cells: barriers and opportunities

Cited by 12 publications

References 58 publications

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Recalcitrance in clonal propagation, in particular of conifers

Developmental switches that hold the key to a revolution in crop biotechnology

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