Genome Size Dynamics and Evolution in Monocots

Abstract

Monocot genomic diversity includes striking variation at many levels. This paper compares various genomic characters (e.g., range of chromosome numbers and ploidy levels, occurrence of endopolyploidy, GC content, chromosome packaging and organization, genome size) between monocots and the remaining angiosperms to discern just how distinctive monocot genomes are. One of the most notable features of monocots is their wide range and diversity of genome sizes, including the species with the largest genome so far reported in plants. This genomic character is analysed in greater detail, within a phylogenetic context. By surveying available genome size and chromosome data it is apparent that different monocot orders follow distinctive modes of genome size and chromosome evolution. Further insights into genome size-evolution and dynamics were obtained using statistical modelling approaches to reconstruct the ancestral genome size at key nodes across the monocot phylogenetic tree. Such approaches reveal that while the ancestral genome size of all monocots was small (1C = 1.9 pg), there have been several major increases and decreases during monocot evolution. In addition, notable increases in the rates of genome size-evolution were found in Asparagales and Poales compared with other monocot lineages.

Does Large Genome Size Limit Speciation in Endemic Island Floras?

“…Further Knight et al [9] proposed the large genome constraint hypothesis (LGCH) that suggests that species with large genomes are less likely to generate progenitor species. The LGCH is in agreement with the general observation that most angiosperm species have small genomes, with a mode, median, and mean genome size (1C) of just 0.6, 2.6, and 6.2 pg, respectively [10]. The LGCH echoes point of view that larger genomes are maladaptive, as they may constrain growth [11], and evolved in populations with smaller effective population size and hence low efficacy of natural selection [6].…”

Nuclear DNA content in Chilean species of Phycella and Rhodolirium (Amaryllidaceae)

“…The 2C-values of R. montanum and P. ignea are lower to the range reported for Amaryllidaceae which vary from 28 to ca. 164.3 pg (Leitch et al , 2010. A similar situation was observed comparing both species with the diploid taxa of Hippeastrum (range from 26.9 to 31.4 pg) (Naranjo & Poggio 1988).…”

“…Angiosperms are the most intensively studied major group of organisms with published C-values varying about 2000-fold for a number over 4,400 studied species (Leitch et al 2010). However, C-values for South American plants are scarce, which has been a preoccupation for researchers interested in study trends on genome size evolution of global floras .…”

A comparative analysis of membrane intactness and genome integrity in pea,barley, and wheat in response to UVC irradiation

“…This finding allows us to argue that genome size variation and ploidy level influence UVC-induced damage accumulation and account for the observed differences between dicots and monocots and within monocots themselves. As previously reported, these host genome characters are involved in promoting genetic differentiation between monocots and dicots (Leitch et al, 2010) and can stand as an indicator of sensitivity to UVC radiation as previously reported (Heddle and Athanasiou, 1975). The current experimental platform, however, does not allow us to make definite conclusions about this hypothesis.…”