ABSTRACT: Transcript profiling reveals a molecular signature that distinguishes early versus late time to bud set phenotypes in a white spruce full-sib family.
Project description:It is crucial for north temperate tree species like white spruce to control timing of growth cessation and bud set in order to survive winter conditions. While much work has examined both endogenous and exogenous mechanisms influencing this transition within angiosperms, the mechanisms underlying this transition in conifers; including photoperiod perception, growth cessation and development of endodormancy, have been less well-characterized. The objective of this research was to compare the genetic responses of spruce genotypes exhibiting an early transition from active growth to bud initiation with those that delay the transition, to tease apart the molecular mechanisms underlying these complex traits. In order to gain a deeper understanding of how genomic architecture influences bud phenology and related regulatory pathways, transcript levels were quantified using a 25,045 element spruce oligonucleotide microarray. Individuals exhibiting early versus late time to bud set were selected from a large unrelated full-sib family that had been phenotyped multiple years under natural and controlled environment conditions, and harvested at an early and mid stage of bud formation. Progeny designated as early time to bud set were more likely to undergo second flush, particularly under long day (16 h) and constant temperature (20°C) conditions. Approximately 5400 genes were differentially expressed in either or both of the early and late time to bud set phenotypic classes between time points, while ca. 1500 genes were differentially expressed between phenotypic classes at either or both time points. These analyses revealed about 400 genes with putative regulatory roles. The comparison between early and late time to bud set trees revealed a large number of specifically differentially expressed genes in the early developmental stage for bud formation (957 genes, including 53 putative regulators) relative to the later developmental stage (81 genes, including 4 putative regulators). Genes implicated in the circadian cycle, photoperiodic pathway and chromatin remodeling figured prominently in these lists, providing new insight into mechanisms that may regulate bud formation in determinate species such as white spruce.
Project description:White pine weevil is a major pest of conifers in North America, especially for Spruce trees. Constitutive defenses are important in understanding defense mechanisms because they constitute the initial barrier to attacks by weevils and other pests. Resistant and susceptible trees exhibit constitutive differences in spruce. To improve our knowledge of their genetic basis, we compared the constitutive expression levels of 17,825 genes between 20 resistant and 20 susceptible trees in interior spruce (Picea glauca).
Project description:It is crucial for north temperate tree species like white spruce to control timing of growth cessation and bud set in order to survive winter conditions. While much work has examined both endogenous and exogenous mechanisms influencing this transition within angiosperms, the mechanisms underlying this transition in conifers; including photoperiod perception, growth cessation and development of endodormancy, have been less well-characterized. The objective of this research was to compare the genetic responses of spruce genotypes exhibiting an early transition from active growth to bud initiation with those that delay the transition, to tease apart the molecular mechanisms underlying these complex traits. In order to gain a deeper understanding of how genomic architecture influences bud phenology and related regulatory pathways, transcript levels were quantified using a 25,045 element spruce oligonucleotide microarray. Individuals exhibiting early versus late time to bud set were selected from a large unrelated full-sib family that had been phenotyped multiple years under natural and controlled environment conditions, and harvested at an early and mid stage of bud formation. Progeny designated as early time to bud set were more likely to undergo second flush, particularly under long day (16 h) and constant temperature (20M-BM-0C) conditions. Approximately 5400 genes were differentially expressed in either or both of the early and late time to bud set phenotypic classes between time points, while ca. 1500 genes were differentially expressed between phenotypic classes at either or both time points. These analyses revealed about 400 genes with putative regulatory roles. The comparison between early and late time to bud set trees revealed a large number of specifically differentially expressed genes in the early developmental stage for bud formation (957 genes, including 53 putative regulators) relative to the later developmental stage (81 genes, including 4 putative regulators). Genes implicated in the circadian cycle, photoperiodic pathway and chromatin remodeling figured prominently in these lists, providing new insight into mechanisms that may regulate bud formation in determinate species such as white spruce. A clonally replicated QTL mapping population (cross C94-1-2516, M-bM-^YM-^@77111 M-CM-^W M-bM-^YM-^B2388), previously characterized by Pelgas et al. (2011), was used for this study. Phenotypic data collected between 2006-2008 was used to identify extremes for time to bud set within the QTL population. Genotypes falling within the lower quartile for time to bud set for at least three of six experiments were designated as early time to bud set, while genotypes falling within the upper quartile for time to bud set for at least three of six experiments were designated as late time to bud set. Shoot tips from four ramets of each genotype were harvested for molecular analysis. Two ramets were harvested at the first sign of bud formation (Time 1) and the remaining two ramets were harvested six weeks later at which time the majority of seedlings were at the mid stage of bud set (Time 2). Microarray hybridizations were conducted to make the following comparisons: a comparison of bud development (Time 1 v. Time 2) in early time to bud set seedlings, a comparison of bud development (Time 1 v. Time 2) in late time to bud set seedlings, and a comparison of early and late time to bud set seedlings within early stages of bud formation or mid stage of bud formation. Each of two biological replicates for each time point and each phenotypic class was hybridized.
Project description:White pine weevil is a major pest of conifers in North America, especially for Spruce trees. Constitutive defenses are important in understanding defense mechanisms because they constitute the initial barrier to attacks by weevils and other pests. Resistant and susceptible trees exhibit constitutive differences in spruce. To improve our knowledge of their genetic basis, we compared the constitutive expression levels of 17,825 genes between 20 resistant and 20 susceptible trees in interior spruce (Picea glauca). Twenty hybridizations were performed to compare untreated bark of resistant and susceptible trees.RNA isolated from each of the 20 individual untreated resistant trees was compared directly against the 20 individual untreated susceptble trees using two hybridizations with a dye flip for each tree pair.
Project description:Tree improvement programs select genotypes for faster growth, at both early and late stages, to increase yields over unimproved material, and the improvement is frequently attributed to genetic control in growth parameters among genotypes. Underutilized genetic variability among genotypes also has the potential to ensure future gains are possible. However, the genetic variation in growth, physiology and hormone control among genotypes generated from different breeding strategies has not been well characterized in conifers. We assessed growth, biomass, gas exchange, gene expression and hormone levels in white spruce seedlings obtained from three different breeding strategies (controlled crosses, polymix pollination, open pollination) using parents grafted into a clonal seed orchard in Alberta, Canada. A pedigree-based best linear unbiased prediction (ABLUP) mixed model was implemented to quantify variability and narrow-sense heritability for target traits and the levels of several hormones and expression of gibberellin-related genes in apical internodes were also determined. Over the first 2-years of development, the estimated heritabilities for height, volume, total dry biomass, above ground dry biomass, root:shoot ratio and root length, varied between 0.10 and 0.21, with height having the highest value. The ABLUP values showed large genetic variability in growth and physiology traits both between families from different breeding strategies, and within families. The principal component analysis showed that developmental and hormonal traits explained 44.2% and 29.4% of the total phenotypic variation between the three different breeding strategies and two growth groups. In general, controlled crosses from the fast growth group showed the best apical growth, with more accumulation of indole-3-acetic acid, abscisic acid, phaseic acid, and a 4-fold greater gene expression of PgGA3ox1 in genotypes from controlled crosses versus those from open pollination, but in some cases, open-pollination from the fast and slow growth groups showed the best root development, higher water use efficiency (iWUE and δ13C) and more accumulation of zeatin and isopentenyladenosine. In conclusion, tree domestication can lead to trade-offs between growth, carbon allocation, photosynthesis, hormone levels and gene expression, and we encourage the use of this phenotypic variation identified in improved and unimproved trees to advance white spruce tree improvement programs.