关于胚乳演化起源的一个假设有了新证据

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关于胚乳演化起源的一个假设有了新证据


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[Nature]关于胚乳演化起源的一个假设有了新证据

开花植物（被子植物）显著成功背后的一个因素也许是胚胎以及二次受精的一个产物——胚乳的发育。一个多世纪以前，科学家提出两个不同的假设来解释胚乳的演化起源，此后这两个假设一直将植物发育领域分成两个学派。Nowack等人所提出的新证据倾向于支持其中的一个假设，即著名植物学家Eduard Strasburger所提出的假设。一种含有一个来自母系的双倍体胚乳、而不是一个来自双亲的三倍体胚乳的拟南芥突变体，其种子被发现能够发育成可存活的植物。这表明雌性生殖结构是胚乳的来源，并且与认为胚乳的产生需要基因组印记的观点是不相符的，该观点认为，一个等位基因的表达取决于这个等位基因是由双亲中的哪一方贡献的。
Nature 447, 312-315 (17 May 2007) | doi:10.1038/nature05770; Received 29 November 2006; Accepted 23 March 2007; Published online 29 April 2007


Bypassing genomic imprinting allows seed development
Moritz K. Nowack1, Reza Shirzadi2, Nico Dissmeyer1, Andreas Dolf3, Elmar Endl3, Paul E. Grini2 & Arp Schnittger1

University group at the Max Planck Institute for Plant Breeding Research, Max-Delbrück-Laboratorium, Department of Botany III, University of Cologne, Carl-von-Linné-Weg 10, D-50829 Cologne, Germany
Department of Molecular Biosciences, University of Oslo, PO Box 1041 Blindern, N-0316 Oslo, Norway
Institute of Molecular Medicine and Experimental Immunology, Sigmund-Freud-St?? 25, D-53105 Bonn, Germany
Correspondence to: Arp Schnittger1 Correspondence and requests for materials should be addressed to A.S. (Email: schnitt@mpiz-koeln.mpg.de).


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In developing progeny of mammals the two parental genomes are differentially expressed according to imprinting marks, and embryos with only a uniparental genetic contribution die1, 2, 3. Gene expression that is dependent on the parent of origin has also been observed in the offspring of flowering plants, and mutations in the imprinting machinery lead to embryonic lethality, primarily affecting the development of the endosperm—a structure in the seed that nourishes the embryo, analogous to the function of the mammalian placenta4. Here we have generated Arabidopsis thaliana seeds in which the endosperm is of uniparental, that is, maternal, origin. We demonstrate that imprinting in developing seeds can be bypassed and viable albeit smaller seedlings can develop from seeds lacking a paternal contribution to the endosperm. Bypassing is only possible if the mother is mutant for any of the FIS-class genes, which encode Polycomb group chromatin-modifying factors. Thus, these data provide functional evidence that the action of the FIS complex balances the contribution of the paternal genome. As flowering plants have evolved a special reproduction system with a parallel fusion of two female with two male gametes, our findings support the hypothesis that only with the evolution of double fertilization did the action of the FIS genes become a requirement for seed development. Furthermore, our data argue for a gametophytic origin of endosperm in flowering plants, thereby supporting a hypothesis raised in 1900 by Eduard Strasburger.