Detection of quantitative trait loci influencing growth trajectories of adventitious roots in Populus using functional mapping

Abstract

The capacity to root from cuttings is a key factor for the mass deployment of superior genotypes in clonal forestry. We studied the genetic basis of rooting capacity by mapping quantitative trait loci (QTLs) that control growth rate and form of root traits in a full-sib family of 93 hybrids derived from an interspecific cross between two Populus species, P. deltoides and P. euramericana. The hybrid family was typed for different marker systems (including SSRs, AFLPs, RAPDs, ISSRs, and SNPs), leading to the construction of two linkage maps based on the female P. deltoides (D map) and male P. euramericana (E map) with a pseudotestcross mapping strategy. The two maps were scanned by functional mapping to detect QTLs that control early growth trajectories of two rooting traits, maximal single-root length and the total number of roots per cutting, measured at five time points in water culture. Of the six QTLs detected for these two growth traits, only one is segregating in P. deltoides with poor rooting capacity, while the other five are segregating in P. euramericana showing good rooting capacity. Tests with functional mapping suggest different developmental patterns of the genetic effects of these root QTLs in time course. Five QTLs were detected to change their effects on root growth trajectories with time, whereas one detected to affect root growth consistently in time course. Knowledge about the genetic and developmental control mechanisms of root QTLs will have important implications for the genetic improvement of vegetative propagation traits in Populus.

Comparative genome mapping among Populus adenopoda, P. alba, P. deltoides, P. euramericana and P. trichocarpa

“…These experimental populations provide an unique opportunity for comparative mapping in the model system-an opportunity that has been further enhanced by the whole genome sequence of a female P. trichocarpa tree released (http:// genome.jgi-psf.org/Poptr1_1/Poptr1_1.home.html and http:// www.phytozome.net/poplar ) (Tuskan et al, 2006). Up to now, 16 mapping works have been published in Populus, leading to the construction of 30 maps relating to 10 poplar species in Populus, Aigeiros and Tacamahaca sections (Cervera et al, 2004;Gaudet et al, 2008;Zhang et al, 2009;Pakull et al, 2009;Paolucci et al, 2010). Several comparative maps with Populus consensus map (based on a P. trichocarpa and P. deltoids background) (Yin et al, 2004 or the physical map of P. trichocarpa showed high degree of synteny and provided a direct link to P. trichocarpa genome sequence Zhang et al, 2009;Pakull et al, 2009;Paolucci et al, 2010).…”

“…Up to now, 16 mapping works have been published in Populus, leading to the construction of 30 maps relating to 10 poplar species in Populus, Aigeiros and Tacamahaca sections (Cervera et al, 2004;Gaudet et al, 2008;Zhang et al, 2009;Pakull et al, 2009;Paolucci et al, 2010). Several comparative maps with Populus consensus map (based on a P. trichocarpa and P. deltoids background) (Yin et al, 2004 or the physical map of P. trichocarpa showed high degree of synteny and provided a direct link to P. trichocarpa genome sequence Zhang et al, 2009;Pakull et al, 2009;Paolucci et al, 2010). Most of these comparative maps are constructed for species of Populus or Aigeiros section and Tacamahaca section, few comparative mapping was actualized based on these three sections altogether.…”

“…Poplar microsatellite (simple sequence repeat, SSR) markers, abundantly available on the website (http:// www.ornl.gov/sci/ipgc/ssr_resources.htm) have been used for many genetic maps in both Populus and the related genus Salix (Hanley et al, 2002;Cervera et al, 2004;Yin et al, 2004;Hanley et al, 2006;Gaudet et al, 2008;Woolbright et al, 2008;Pakull et al, 2009;Zhang et al, 2009;Berlin et al, 2010;Paolucci et al, 2010;Liu et al, 2011), and allow an alignment of these maps to each other and to the P. trichocarpa genomic sequence and the consensus map, providing much information for comparative genomic studies of different species in the genus. The dominant markers (for example amplified fragment length polymorphism (AFLP) and sequence related amplified polymorphism (SRAP) (Vos et al, 1995;Li and Quiros, 2001) are unvalued for comparative mapping but can enrich the maps.…”

“…The pseudo-testcross strategy described by Grattapaglia and Sederoff (1994) is usually used in the mapping of forest trees. In this research the genetic maps of the white poplar were constructed using the same mapping strategy and software as two kinds of black poplar maps reported by Zhang et al (2009) in order to compare between them (here P. deltoides and P. euramericana are regarded as deputies of the species in the section Aigeiros Duby, because the maps of P. deltoides and P. euramericana were constructed based on the common set of SSR markers in our laboratory). Therefore, the objectives of the present study were: (1) to provide genetic linkage maps for P. adenopoda and P. alba based on a combination of SSR and SRAP markers data by the twoway pseudo-testcross strategy and Mapmarker3.0 (Grattapaglia and Sederoff, 1994;Lander, 1987) (2) to align our white poplar maps and the black poplar maps to the physical map of P. trichocarpa using BLAST and the sequence of SSR primers in order to evaluate the degree of macro-synteny and macro-colinearity in Populus, Aigeiros and Tacamahaca sections genomes.…”

“…A total of 93 genotypes randomly selected from the 450 seedlings were used for map construction (Zhang et al, 2009). As the white poplar maps, the pseudo-test cross strategy and MapMaker 3.0 were used to construct two black poplar maps based on AFLP, ISSR, RAPD, SSR and SNP markers.…”