Two unigene datasets of Pinus taeda and Pinus pinaster were screened to detect di-, tri- and tetranucleotide repeated motifs using the SSRIT script. A total of 419 simple sequence repeats (SSRs) were identified, from which only 12.8% overlapped between the two sets. The position of the SSRs within their coding sequences were predicted using FrameD. Trinucleotides appeared to be the most abundant repeated motif (63 and 51% in P. taeda and P. pinaster, respectively) and tended to be found within translated regions (76% in both species), whereas dinucleotide repeats were preferentially found within the 5'- and 3'-untranslated regions (75 and 65%, respectively). Fifty-three primer pairs amplifying a single PCR fragment in the source species (mainly P. taeda), were tested for amplification in six other pine species. The amplification rate with other pine species was high and corresponded with the phylogenetic distance between species, varying from 64.6% in P. canariensis to 94.2% in P. radiata. Genomic SSRs were found to be less transferable; 58 of the 107 primer pairs (i.e. 54%) derived from P. radiata amplified a single fragment in P. pinaster. Nine cDNA-SSRs were located to their chromosomes in two P. pinaster linkage maps. The level of polymorphism of these cDNA-SSRs was compared to that of previously and newly developed genomic-SSRs. Overall, genomic SSRs tend to perform better in terms of heterozygosity and number of alleles. This study suggests that useful SSR markers can be developed from pine ESTs.

Microsatellites are widely used as genetic markers because they are co-dominant, multiallelic, easily scored and highly polymorphic. A major drawback of microsatellite markers is the time and cost required to characterise them. We have developed a novel technique to reduce this cost by producing a microsatellite-rich PCR profile from genomic DNA which was cloned to yield a genomic library enriched for microsatellites. Sequence data and subsequent allele scoring within pedigrees revealed that these microsatellites retained their original repeat length and segregated normally. This technique permits genomic amplification with only one specific primer. Together with enrichment, the savings in primer costs reduces the cost of microsatellite characterisation considerably.

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We conducted a controlled crossing experiment to examine the effects of maternal and paternal parentage, the size of the pollen load, and prior fruit production on the proportion of flowers that set fruit, seed number per fruit and seed weight in a natural population of Campanula americana. Effects due to the maternal parent were large for all measures of fruit and seed production, while the paternal parent had a significant effect only upon mean seed weight. As the number of prior fruits on the maternal plant increased the probability that a flower would produce a mature fruit, the number of seeds per fruit, and total seed weight per fruit all decreased. We found no effect of the size of the pollen loads used in this study on fruit or seed production. These results are consistent with those of other studies that suggest in natural plant populations maternal effects, especially environmental maternal effects, can have an overwhelming effect on fruit and seed production and on seed characteristics.

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Wood formation was investigated at five heights along the bole for two unrelated trees of Pinus radiata. Both trees showed clear gradients in wood properties from the base to the crown. Cambial cells at the base of the tree were dividing 3.3-fold slower than those at the crown, while the average thickness of cell walls in wood was highest at the base. Cell wall thickness showed an overall correlation coefficient of >0.7 with wood density in both genotypes. Microscopic examination of developing tracheids showed that 33% of cells had formed secondary cell walls at the base of the tree, reducing to 3% at the crown. In total, 455 genes differentially expressed in developing xylem tissue from either the base or the crown were identified using modified differential display. RT-PCR analysis of 156 genes confirmed differential expression for 77%. Of the genes tested, 73% showed gradients in transcript abundance either up or down the bole of the tree, although the steepness of the gradients differed between genes. Genes involved in cell division and expansion tended to be more highly expressed in the crown of the tree, and two putative cell-cycle repressor genes were expressed 2-fold higher at the base. Conversely, transcripts of genes involved in secondary wall thickening were more abundant at the base of the tree. These results suggest that differences in the rate of cambial cell division, differences in the rate and duration of tracheid wall thickening, and differences in gene expression underpin the gradients of wood properties found in pines.

No abstract

To examine the effects of maternal and paternal parentage and the size of the pollen load on seed size and weight and on progeny performance we conducted a controlled crossing experiment using a natural population of Campanula americana. We found that seed size was positively correlated with early seedling performance for all but one of traits we measured (days to emergence), but was not significantly correlated with any of the later vegetative measures or reproductive output. We detected significant effects due to the maternal parent for the vegetative traits days to emergence, days to first leaf, and final plant height, as well as total seed weight, and mean seed weight per fruit. Significant paternal effects were found for all of the seedling traits except number of leaves after vernalization. The progeny from fruits receiving high pollen loads significantly outperformed the progeny from fruits receiving low pollen loads for the traits days to first and second leaf, numbers of leaves after vernalization, and days to first flower. These results not only demonstrate the importance of parentage and seed weight on progeny performance, but also indicate that variations in the size of the pollen load may be important in seedling establishment in natural populations.