Evolution of Genome Size in Brassicaceae

Abstract

The tree roots at an ancestral genome size of approximately 1x = 0.2 pg. Arabidopsis thaliana (1C = 0.16 pg; approximately 157 Mbp) has the smallest genome size in Brassicaceae studied here and apparently represents an evolutionary decrease in genome size. Two other branches that represent probable evolutionary decreases in genome size terminate in Lepidium virginicum and Brassica rapa. Branches in the phylogenetic tree that represent probable evolutionary increases in genome size terminate in Arabidopsis halleri, A. lyrata, Arabis hirsuta, Capsella rubella, Caulanthus heterophyllus, Crucihimalaya, Lepidium sativum, Sisymbrium and Thlaspi arvense. Branches within one clade containing Brassica were identified that represent two ancient ploidy events (2x to 4x and 4x to 6x) that were predicted from published comparative mapping studies.

Development and linkage mapping of unigene-derived microsatellite markers in Brassica rapa L.

“…LG A9 (126.2 cM) was the longest, LG A4 (69.2 cM) was the shortest, and the markers density varied across LGs for this map (Table 2). Based on the estimated DNA content of 529 Mbp for B. rapa (Johnston et al 2005), the estimated physical average spacing between markers was 1.77 Mbp in the current map. The UGMS marker loci were evenly distributed on most of the B. rapa LGs, especially on A3, A6 and A9 with a total of 10, 12 and 10 UGMS marker loci, respectively.…”

The shrunken genome of Arabidopsis thaliana

“…However, when there were alternatives that seemed equally plausible, we chose the alignment that minimized the number of potentially informative characters to avoid biasing the results. Sequences generated for this study were submitted to GenBank with accession Johnston et al (2005) The shrunken genome of Arabidopsis thaliana 259 numbers as given in Table 1. Voucher specimens were deposited at M and DUKE.…”

“…All measurements used B. oleracea, B. rapa, Matthiola incana, or some mixture of those three species as standards and were recorded as a ratio of the size of the plant being measured to B. oleracea. These ratios were converted into 2C values using a published value of 0.710 pg for B. oleracea (Johnston et al 2005). One C value (Cardamine amara) was obtained from Johnston et al (2005).…”

“…340 genera and 3,700 species , has great variability in life history, habit, and ecology, and is known to have undergone recurrent polyploidization over the course of its evolution. The family displays a moderate diversity of genome sizes, (Johnston et al 2005;Nagl et al 1983) and a range of monoploid chromosome numbers (Warwick and Al-Shehbaz 2006). Finally, there is a considerable amount of genome level information already available from multiple genera and species within Brassicacae in addition to A. thaliana.…”

“…A few studies have also approached the evolution of genome size within a phylogenetic context (Bennetzen and Kellogg 1997;Jakob et al 2004;Soltis et al 2003;Weiss-Schneeweiss et al 2006). However, only one study has focused on genome size evolution among the taxa near to Arabidopsis thaliana (Johnston et al 2005). But, it relied on only one marker for the reconstruction of the phylogeny and did not apply significance tests to the evolution of the character.…”