蛇菰科與檀香目植物親緣關係及分子演化之研究

Abstract

Many holoparasitic plants have reduced plastid genomes and exhibit multiple morphological reductions resulted from evolutionary convergence. The root-parasitic Balanophora (Balanophoraceae) displays one of the most extreme reduction and modification in morphologies and was reported to have enormous rate acceleration in nuclear 18S ribosomal gene. However, the molecular evolution of nuclear genes in parasitic plants remain largely unexplored and despite the family Balanophoraceae has been shown to have a close relation with the basal core eudicots order, Santalales, the exact phylogenetic position of Balanophoraceae remains unsolved. In this dissertation, molecular phylogenetic analyses were performed to resolve the phylogenetic relationships between Balanophoraceae and other Santalales taxa. To better our understanding of the molecular evolution of nuclear genes in holoparasitic plants, a considerable number of floral MADS-box genes were identified and the conservation of gene structure were examined. The molecular evolutionary rates of six protein-coding genes of holoparasitic Balanophora and hemiparasitic Santalales were compared with photosynthetic core eudicots and the expressions of floral B-class genes were further examined in B. laxiflora. Sequences from nuclear RPB2 genes and two floral homeotic B-class genes, PI and TM6 were used to elucidate the phylogenetic relationships between Balanophoraceae and other Santalales taxa. 67 MADS-box gene loci were obtained from three Balanophoraceae and 14 other Santalales species, which all exhibit a high conservation in gene sequence and structure. Several alternatively spliced transcripts of the MADS-box gene were also identified in our screening, implying potential important roles of these transcripts during floral development. The floral B-class genes in B. laxiflora showed a differential expression pattern in floral and vegetative organs. The evolutionary rate analyses showed that nuclear protein-coding gene sequences have much lower substitution rates than those of nuclear 18S and mitochondrial matR genes, which provide promising markers for phylogenetic analyses. All of the phylogenetic analyses supported that Balanophoraceae is a derived holoparasitic lineage within the parasitic Santalales. Moreover, two agamospermic Balanophora species were found in Taiwan; the morphological features were compared, the first phylogenetic analysis of the genus employing DNA sequences are presented and the host species were further confirmed by amplifying chloroplast matK sequences from the connected root tissues. The molecular evidences showed the two agamospermic Balanophora species in Taiwan are belonging to B. japonica and B. yakushimensis and they are phylogenetically grouped with dioecious B. laxiflora.