Rice Epigenetics Helps Vindicate Lamarck
Epigenetic Inheritance in Rice Plants
KEIKO AKIMOTO1 , HATSUE KATAKAMI1 , HYUN-JUNG KIM1, EMIKO OGAWA1 ,
CECILE M. SANO2, YUKO WADA1 and HIROSHI SANO1,*
Annals of Botany 100: 205–217, 2007
doi:10.1093/aob/mcm110, available online at www.aob.oxfordjournals.org
Who would have thought that Jean Baptiste de Lamarck's (1744-1829) theory of evolution, based on inheritance of acquired characteristics would one day be supported by the study of epigenetics in rice plants?
The study conducted by Keiko Akimoto etal, in epigenetics of the rice plant Oryza sativa ssp. japonica has provided evidence that acquired traits were stably inherited by offspring. It would seem that changes to the structure of chromatin (DNA and Histone proteins that make up the chromosomes) but not to the DNA base sequence, causes a change in gene expression or traits. These changes are heritable and passed onto the next generation as a type of Lamarckian inheritance.
DNA methylation (adding a methyl group to the 5th carbon of the ctyosine base) is one way of modifying DNA without changing the original DNA sequence (epigenetics). Demethylation (removing the methyl group from cytosine) is also a way of modifying DNA epigenetically. In this study artificial demethylation of cytosine was achieved by treating japonica rice seeds with 5-azadeoxycytidine (methylation inhibitor). This process was lethal to most of the seedlings that germinated but a small percentage survived. Of these surviving seedlings a line that bred true for dwarfism over 9 successive generations (1998-2006) was selected for investigation. A wild form of the rice was the control. Seedlings of the control and the test group were inoculated with the rice blight pathogen Xanthomonas oryzae and various DNA molecular tests for methylation/demethylation sites in the genome were carried out. To direct the search researchers targeted the regions near the leaf blight resistant gene, Xa21.
Results of the molecular tests revealed that infected wild type rice displayed no transcripts (copies) of the Xa21 gene, while the test group rice showed heavy transcription of the Xa21 gene. Methylation analysis by DNA Blot Hybridisation also revealed that the promoter region upstream of the Xa21 gene was methylated in the wild type rice. The test group however were totally void of methylated cytosine. This indicated that DNA methylation had silenced the disease resistant gene Xa21 in the wild type rice and DNA demethylation had activated the gene. This acquired resistance was stably inherited by the progeny. Other studies have also revealed that demethylation can occur naturally when plants are placed under stress, be it environmental or pathogenic.
Lamarck's shouts of vindication can almost be heard from here, as this evidence supports his theory that acquired characteristics during an organism's lifetime are inherited by the next generation. There may also be some evolutionary biologists and X-teachers that will be able to change socks now that they have taken their foot out of their mouth. Well, at least long enough to be able to eat some Lamarckian humble pie!
Gerard Scalia
KEIKO AKIMOTO1 , HATSUE KATAKAMI1 , HYUN-JUNG KIM1, EMIKO OGAWA1 ,
CECILE M. SANO2, YUKO WADA1 and HIROSHI SANO1,*
Annals of Botany 100: 205–217, 2007
doi:10.1093/aob/mcm110, available online at www.aob.oxfordjournals.org
Who would have thought that Jean Baptiste de Lamarck's (1744-1829) theory of evolution, based on inheritance of acquired characteristics would one day be supported by the study of epigenetics in rice plants?
The study conducted by Keiko Akimoto etal, in epigenetics of the rice plant Oryza sativa ssp. japonica has provided evidence that acquired traits were stably inherited by offspring. It would seem that changes to the structure of chromatin (DNA and Histone proteins that make up the chromosomes) but not to the DNA base sequence, causes a change in gene expression or traits. These changes are heritable and passed onto the next generation as a type of Lamarckian inheritance.
DNA methylation (adding a methyl group to the 5th carbon of the ctyosine base) is one way of modifying DNA without changing the original DNA sequence (epigenetics). Demethylation (removing the methyl group from cytosine) is also a way of modifying DNA epigenetically. In this study artificial demethylation of cytosine was achieved by treating japonica rice seeds with 5-azadeoxycytidine (methylation inhibitor). This process was lethal to most of the seedlings that germinated but a small percentage survived. Of these surviving seedlings a line that bred true for dwarfism over 9 successive generations (1998-2006) was selected for investigation. A wild form of the rice was the control. Seedlings of the control and the test group were inoculated with the rice blight pathogen Xanthomonas oryzae and various DNA molecular tests for methylation/demethylation sites in the genome were carried out. To direct the search researchers targeted the regions near the leaf blight resistant gene, Xa21.
Results of the molecular tests revealed that infected wild type rice displayed no transcripts (copies) of the Xa21 gene, while the test group rice showed heavy transcription of the Xa21 gene. Methylation analysis by DNA Blot Hybridisation also revealed that the promoter region upstream of the Xa21 gene was methylated in the wild type rice. The test group however were totally void of methylated cytosine. This indicated that DNA methylation had silenced the disease resistant gene Xa21 in the wild type rice and DNA demethylation had activated the gene. This acquired resistance was stably inherited by the progeny. Other studies have also revealed that demethylation can occur naturally when plants are placed under stress, be it environmental or pathogenic.
Lamarck's shouts of vindication can almost be heard from here, as this evidence supports his theory that acquired characteristics during an organism's lifetime are inherited by the next generation. There may also be some evolutionary biologists and X-teachers that will be able to change socks now that they have taken their foot out of their mouth. Well, at least long enough to be able to eat some Lamarckian humble pie!
Gerard Scalia
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