Project description:Polyploidization as the consequence of 2n gamete formation is a prominent mechanism in plant evolution. Studying its effects on the genome and its expression has both basic and applied interest. We crossed two diploid (2n=2x=16) M. sativa plants, a subsp. falcata seed parent and a coerulea x falcata pollen parent that produce a mixture of n and 2n eggs and pollen, respectively. Such cross produced full-sib diploid and tetraploid (2n=4x=32) progenies, the latter being the result of bilateral sexual polyploidization (BSP). These unique materials allowed us to investigate the effects of BSP, and separating the effect of intraspecific hybridization from those of polyploidization by comparing 2x with 4x full sib progeny plants. SSR marker segregation demonstrated tetrasomic inheritance for all chromosomes but one, demonstrating that these neotetraploids are true autotetraploids. BSP brought about increased biomass, earlier flowering, higher seed set and weight, larger leaves with larger cells. Microarray analyses with M. truncatula gene chips showed that several hundred genes, related to diverse metabolic functions, changed their expression level as a consequence of polyploidization. In addition, cytosine methylation increased in 2x but not in 4x hybrids. Our results indicate that sexual polyploidization induce significant transcriptional novelty, possibly mediated in part by DNA methylation, and phenotypic novelty that can be at the base of improved adaptation and reproductive success of tetraploid M. sativa with respect to its diploid progenitor. These polyploidy-induced changes may have promoted the adoption of tetraploid alfalfa in agriculture. Gene expression analysis of leaves at the vegetative stage of two Medicago sativa genotypes (PG-F9 and 12P) compared with three F1 diploid lines and three F1 tetraploid lines originating from crossing PG-F9 x 12P. Three biological replicates were taken for each sample, resulting in a total of twenty-four samples.
