Polyploids and domesticated species Natalia Alvarez UW Madison March 20th 2007 Polyploidy and its effects It is estimated that 70 of the flowering plants has polyploidy in their history Masterson 1994 Increased cell size and gigas effect in some organs Changes in shape and texture of organs Greater ability to colonize new habitats than diploid ancestors Reduction in fertility and seed production Stebbins 1971 The role of polyploidy in crop improvement Gene buffering Slower response to selection but more adaptive potential Dosage effect additive effect of the alleles increases the number of phenotypes Increased allele diversity and heterozygosis more possible allele combinations and opportunities for breeding Novel phenotypic variation genome interactions and changes in gene expression in new synthesized allopolyploids Did polyploidy confer advantages for plant domestication Survey of 244 crops species belonging to 11 monocot and 48 dicot families Chromosome number obtained from literature Neopolyploids determined by comparing with the smallest chromosome number in its respective genus Determination of Paleopolyploids Two criteria Goldblatt 1980 n 11 and Grant 1963 n 13 The frequency of polyploids in crops was compared with estimates for angiosperms monocots and dicots Hilu 1993 Did polyploidy confer advantages for plant domestication If yes polyploids frequency should be higher for crops than for angiosperms Angiosperms estim Total crops of species counted Polyploidy n 13 Polyploidy Grant 1963 Goldblatt 1980 Lewis 1980b 47 75 244 55 75 n 11 Not significant difference was found Therefore domestication would not favored polyploids over diploids Comparing at the family level Polyploids frequency was not statistically different in 5 of the selected families except in Dioscoreaceae Hilu 1993 Are polyploids more frequent in perennial plants Polyploidy Polyploidy of n 11 n 13 species Goldblatt 1980 counted Grant 1963 Lewis 1980b Angiosperms estim 47 75 Total crop annuals 76 46 68 Total crop perennials 146 60 76 The frequencies of annual vs perennial polyploid crops were statistically similar contrasting with the proposed idea that perennial polyploids have a selection advantage Hilu 1993 What happens after polyploid formation In autopolyploids Genomes act independently Gene expression Dosage effect linear relationship between gene expression and number of gene copies Non dosage regulation over under regulation What happens after polyploid formation In allopolyploids Genomic changes Diploidization and structural evolution Intergenomic colonization Nuclear cytoplasmic interactions Rapid genome changes Gene changes Divergence Silencing Intergenomic gene conversion Differential rate of evolution Bringing the story to the cotton Parental genomes from different continents Maternal A genome from Africa Paternal D genome from the New World Polyploidization 1 5 Mya Origin of 5 Allopolyploid species http www athenapub com nwdom1 htm New World The progenitors Africa G raimondii 2n 2x 26 The descendants 2n 4x 52 The domesticated species G arboreum G herbaceum G darwinii G tomentosum G mustelinum G hirsutum G barbadense G hirsutum G barbadense G arboreum G herbaceum http www eeob iastate edu faculty WendelJ fiberevolution htm Domestication in the New World Archaeological reports of cotton fabrics found in prehistoric ruins in Arizona Gossypium hirsutum evolved in Mexico The oldest archaeological specimens were found in Tehuacan and are tentatively dated at 3400 to 2300 B C Gossypium barbadense is the second species of New World cotton Peruvian archaeological excavations found cotton textiles of 2500 B C http www mayanindians com mayan weavers html http www hno harvard edu gazette 2002 01 24 09 textile html What happens in the nucleus of the polyploid cotton Gene and genome evolution hypothesis Adams and Wendel 2004 Genomic interactions Intergenomic colonization Repetitive sequences specific from A genome are found in the D genome in Gossypium polyploids Transposable elements might be related Zhao et al 1998 Genomic interactions Rapid genomic changes and silencing Immediate consequences of allopolyploidization seem to occur in evolutionary timescale Near complete genomic stasis across generations of synthetic allopolyploids is observed It contrast with evidence from other synthetic allopolyploids Similar gene silencing within synthetic allopolyploids and respect to the natural allotetraploid of G hirsutum Adams et al 2003 Evolution of duplicated genes Biased expression toward one homeologue or the other Some genes show organ specific reciprocal silencing adhA gene in G hirsutum Transcript level Adams et al 2003 Evolution of duplicated genes Interlocus concerted evolution Sequences of ITS regions and 5 8S ribosomal gene in the AD genome species and their diploid progenitors show homogeneity Four of the 5 allopolyploids homogenized the 4 loci to the D like form and one to the A like form Gene tree Wendel et al 1995 Evolution of duplicated genes Differential rate of evolution Nucleotide diversity at homeologous locus of adhA and gene in G hirsutum and G barbadense was higher in the D genome than in the A genome of the allopolyploids The results were observed also for adhC gene Small et al 1999 Small and Wendel 2002 References Adams K and Wendel J 2004 Exploring the genomic mysteries of polyploidy Biol Journal of the Linnean Society 82 573 581 Hilu K 1993 Polyploidy and the evolution of domesticated plants Amer Journal of Botany 80 12 1494 1499 Stebbins G 1971 Chromosomal evolution in higher plants Ch 5 Edward Arnold London Udall J and Wendel J 2006 Polyploidy en crop improvement The Plant Genome A supplement to Crop Science Nov 2006 No 1 Wendel J 2000 Genome evolution in polyploids Plant Molecular Biology 42 225 249
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