Abstract
A Populus deltoides×Populus trichocarpa F1
pedigree was analyzed for quantitative trait loci (QTLs)
affecting ectomycorrhizal development and for microarray
characterization of gene networks involved in this symbiosis.
A 300 genotype progeny set was evaluated for its
ability to form ectomycorrhiza with the basidiomycete
Laccaria bicolor. The percentage of mycorrhizal root tips
was determined on the root systems of all 300 progeny and
their two parents. QTL analysis identified four significant
QTLs, one on the P. deltoides and three on the P.
trichocarpa genetic maps. These QTLs were aligned to
the P. trichocarpa genome and each contained several
megabases and encompass numerous genes. NimbleGen
whole-genome microarray, using cDNA from RNA extracts
of ectomycorrhizal root tips from the parental genotypes P.
trichocarpa and P. deltoides, was used to narrow the
candidate gene list. Among the 1,543 differentially
expressed genes (p value≤0.05; ≥5.0-fold change in
transcript level) having different transcript levels in mycorrhiza
of the two parents, 41 transcripts were located in the
QTL intervals: 20 in Myc_d1, 14 in Myc_t1, and seven in
Myc_t2, while no significant differences among transcripts
were found in Myc_t3. Among these 41 transcripts, 25
were overrepresented in P. deltoides relative to P. trichocarpa;
16 were overrepresented in P. trichocarpa. The
transcript showing the highest overrepresentation in P.
trichocarpa mycorrhiza libraries compared to P. deltoides
mycorrhiza codes for an ethylene-sensitive EREBP-4
protein which may repress defense mechanisms in P.
trichocarpa while the highest overrepresented transcripts
in P. deltoides code for proteins/genes typically associated
with pathogen resistance.
