Epigenomic diversification within the genus Lupinus.

Deciphering the various chemical modifications of both DNA and the histone compound of chromatin not only leads to a better understanding of the genome-wide organisation of epigenetic landmarks and their impact on gene expression but may also provide some insights into the evolutionary processes. Although both histone modifications and DNA methylation have been widely investigated in various plant genomes, here we present the first study for the genus Lupinus. Lupins, which are members of grain legumes (pulses), are beneficial for food security, nutrition, health and the environment. In order to gain a better understanding of the epigenetic organisation of genomes in lupins we applied the immunostaining of methylated histone H3 and DNA methylation as well as whole-genome bisulfite sequencing. We revealed variations in the patterns of chromatin modifications at the chromosomal level among three crop lupins, i.e. L. angustifolius (2n = 40), L. albus (2n = 50) and L. luteus (2n = 52), and the legume model plant Medicago truncatula (2n = 16). Different chromosomal patterns were found depending on the specific modification, e.g. H3K4me2 was localised in the terminal parts of L. angustifolius and M. truncatula chromosomes, which is in agreement with the results that have been obtained for other species. Interestingly, in L. albus and L. luteus this modification was limited to one arm in the case of all of the chromosomes in the complement. Additionally, H3K9me2 was detected in all of the analysed species except L. luteus. DNA methylation sequencing (CG, CHG and CHH contexts) of aforementioned crop but also wild lupins such as L. cosentinii (2n = 32), L. digitatus (2n = 36), L. micranthus (2n = 52) and L. pilosus (2n = 42) supported the range of interspecific diversity. The examples of epigenetic modifications illustrate the diversity of lupin genomes and could be helpful for elucidating further epigenetic changes in the evolution of the lupin genome.