The rate of nucleotide substitution is a fundamental quantity in the study of molecular evolution. To characterize the evolution of DNA sequences, we need to know how fast they evolve. Furthermore, comparing the substitution rates among genes helps us understand the mechanism of nucleotide substitution in evolution and to date the divergence between species. The patterns of gene evolution in gymnosperms are very poorly understood. Therefore, we are studying the evolution of selected coding and noncoding chloroplast and mitochondrial sequences in a large group of gymnosperms. In addition, we are also studying the effects of RNA editing upon the dynamics of DNA evolution. Results from this study will provide the first information about the rates and patterns of DNA evolution in this group of plants.
Allelic variation
Much of the present research effort in molecular biology of forest trees is focused on the structure, function and regulation of genes involved in the processes underlying tree growth and development. In these studies, individual genes are regarded as solitary entities derived from a single individual of a species, giving the impression that each gene represents a single nucleotide sequence shared by all individuals of a species. However, the concept of allelic forms of genes is fundamental to all fields of genetic research. For some genes, even minor nucleotide substitutions have drastic effects on gene function, and consequently on the fitness of an individual. Other genes harbor substantial allelic sequence variations that apparently have no fitness effects. There is much evidence indicating that structural genes have allelic forms encoding products with different structural and regulatory properties. We have found that some genes in forest trees are also represented by more than one nucleotide sequence. It is thus uncertain whether present conclusions about their function and expression will hold when applied to other individuals, populations or species. The purpose of this project is to examine the extent and functional significance of allelic variation of several genes, which are currently subject to detailed scrutiny in molecular biological research on forest trees. To achieve our goals, we are studying sequence variation of a selected group of coding sequences among individuals and populations of Pinus sylvestris. Results from these studies will provide the first information about the significance of allelic variation for current inferences concerning the expression and function of these sequences.
Molecular Phylogenetics
Molecular phylogenetics is the study of evolutionary relationships among organisms or genes using a combination of molecular biology and statistical techniques. We are studying phylogenetic relationships among Eurasian Pinus species using coding and noncoding chloroplast DNA sequences. For several reasons DNA sequence data, are much more powerful for evolutionary studies than morphological and physiological data. First, DNA sequences generally evolve in a much more regular manner than do morphological and physiological characters and therefore can provide a clearer picture of relationships among organisms. Second, molecular data are often much more amenable to quantitative treatments than are morphological data. In particular, we are interested in elucidating the evolutionary history of Pinus krempfii, which is perhaps the least known and studied pine. Pinus krempfii has several morphological and wood anatomical features giving unusual combinations of characters. It has been suggested that the taxon represents a link between the genus Pinus and other genera such as Keteleeria and Pseudolarix of the family Pinaceae, and some students have elevated this taxon to the rank of a monospecific genus in the family Pinaceae. Other authors, however, have only recognized it as a separate Pinus species. Due to the lack of more detailed studies, the evolutionary history and taxonomic position of this unique, flat-needle pine remain uncertain.
Selected publications:
Wang, X-R., Szmidt, A. E. and M-Z. Lu () Genetic evidence for the presence of cytoplasmic DNA in pollen and megagametophytes and maternal inheritance of mitochondrial DNA in Pinus. Forest Genetics 3: 37-44.
Lu, M-Z., Szmidt, A. E. and Wang, X-R. () RNA editing in gymnosperms and its impact on the evolution of the mitochondrial coxI gene. Plant Molecular Biology 37: 225-234
Szmidt, A. E., Lu, M-Z., and Wang, 0X-R. () Effects of RNA editing on the coxI evolution and phylogeny reconstruction. Euphytica: in press.
Wang, X-R., Tsumura, Y., Yoshimaru, H., Nagasaka, K. and Szmidt, A. E. ()Phylogenetic relationships of Eurasian pines (Pinus, Pinaceae) based on chloroplast rbcL, matK, rpl20-rps18 spacer and trnV intron sequences. American Journal of Botany 86: .
Wang, X-R., Szmidt, A. E. and Nguen, H-N. () The phylogenetic position of the endemic flat-needle pine Pinus krempfii (Lec., Pinaceae) from Vietnam, based on PCR-RFLP analysis of chloroplast DNA. Plant Systematics and Evolution 220: 21-36.
