Dissertation Research: Systematics of Harveya Hook. (Orobanchaceae) and the Evolution of Photosynthetic Loci in the Holoparasitic Genera Harveya and Hyobanche L.

论文研究：Harveya Hook 的系统学。

• 批准号: 0104642
• 负责人: Andrea Wolfe
• 金额: --
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-15 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0104642&HistoricalAwards=false
• 关键词: Dissertation; Research; Systematics; Harveya; Hook.

Harveya Hook. (Orobanchaceae) is a genus of parasitic plants native to South Africa. Harveya species parasitize other plants by means of specialized root organs called haustoria. Little is known regarding delimitations of species within Harveya, relationships among species, or if Harveya species are specific to particular host plants. Goals of this study include the examination of morphological characters to determine species delimitations, the inference of phylogenetic history from morphological characters and DNA sequences, and determination of host specificity by excavation of haustoria. In parasitic plants, genes encoding photosynthetic proteins are not functionally constrained. These genes may bear function-reducing mutations. Because parasitic plants obtain nutrients from a host plant rather than through photosynthesis, these mutations are not detrimental to fitness. Therefore, these mutations may be passed to offspring and become fixed in populations. Deterioration or deletion of photosynthetic genes has been documented in parasitic plants of diverse lineage. Another parasite, Hyobanche L., is the sister genus of Harveya. Hyobanche bears mutations in the gene rbcL, a chloroplast gene encoding the large subunit of Rubisco, a protein necessary for photosynthesis. These mutations render rbcL non-functional in this genus. One might expect Harveya to demonstrate similar function-ending mutations in this gene. However, in all Harveya species examined thus far, rbcL encodes a functional protein. Two hypotheses may be invoked to explain the absence of these mutations. (a) The loss of Rubisco functionality has occurred via a different pathway in Harveya than in Hyobanche. (b) Rubisco retains function in Harveya, in facultative photosynthesis or an unknown, non-photosynthetic role. In this study, genes encoding both the small subunit (rbcS) and large subunit (rbcL) will be sequenced in Hyobanche and Harveya to compare functionality. Additionally, RNA and protein products of these genes will be assayed to determine the evolutionary pathway by which Rubisco functionality has been lost in these genera or if Rubisco serves some non-photosynthetic function. The importance of this study is several-fold. South Africa maintains the greatest floral diversity of any temperate region of equal size. However, many species may become endangered as population growth continues, and human habitations expand into wild areas. Conservation efforts will rely on knowledge of the evolutionary history and ecological needs (e.g. suitable plant hosts) of threatened organisms. Secondly, the dichotomy of rbcL functionality in Hyobanche and Harveya provides an ideal system for the study of evolution of photosynthetic genes in non-photosynthetic plants. Furthermore, rbcL and rbcS have an integrated function, but are coded in different genomes of the plant: rbcL in the chloroplast genome and rbcS in the nucleus. Loss of function of one of these genes may result in loss of function in the other. To date, no study has examined if mutations occurring in one genome may be mirrored by mutations in the other. Hyobanche and Harveya offer an excellent framework for investigating this phenomenon.

Harveya Hook. (Orobanchaceae) is a genus of parasitic plants native to South Africa. Harveya species parasitize other plants by means of specialized root organs called haustoria. Little is known regarding delimitations of species within Harveya, relationships among species, or if Harveya species are specific to particular host plants. Goals of this study include the examination of morphological characters to determine species delimitations, the inference of phylogenetic history from morphological characters and DNA sequences, and determination of host specificity by excavation of haustoria. In parasitic plants, genes encoding photosynthetic proteins are not functionally constrained. These genes may bear function-reducing mutations. Because parasitic plants obtain nutrients from a host plant rather than through photosynthesis, these mutations are not detrimental to fitness. Therefore, these mutations may be passed to offspring and become fixed in populations. Deterioration or deletion of photosynthetic genes has been documented in parasitic plants of diverse lineage. Another parasite, Hyobanche L., is the sister genus of Harveya. Hyobanche bears mutations in the gene rbcL, a chloroplast gene encoding the large subunit of Rubisco, a protein necessary for photosynthesis. These mutations render rbcL non-functional in this genus. One might expect Harveya to demonstrate similar function-ending mutations in this gene. However, in all Harveya species examined thus far, rbcL encodes a functional protein. Two hypotheses may be invoked to explain the absence of these mutations. (a) The loss of Rubisco functionality has occurred via a different pathway in Harveya than in Hyobanche. (b) Rubisco retains function in Harveya, in facultative photosynthesis or an unknown, non-photosynthetic role. In this study, genes encoding both the small subunit (rbcS) and large subunit (rbcL) will be sequenced in Hyobanche and Harveya to compare functionality. Additionally, RNA and protein products of these genes will be assayed to determine the evolutionary pathway by which Rubisco functionality has been lost in these genera or if Rubisco serves some non-photosynthetic function. The importance of this study is several-fold. South Africa maintains the greatest floral diversity of any temperate region of equal size. However, many species may become endangered as population growth continues, and human habitations expand into wild areas. Conservation efforts will rely on knowledge of the evolutionary history and ecological needs (e.g. suitable plant hosts) of threatened organisms. Secondly, the dichotomy of rbcL functionality in Hyobanche and Harveya provides an ideal system for the study of evolution of photosynthetic genes in non-photosynthetic plants. Furthermore, rbcL and rbcS have an integrated function, but are coded in different genomes of the plant: rbcL in the chloroplast genome and rbcS in the nucleus. Loss of function of one of these genes may result in loss of function in the other. To date, no study has examined if mutations occurring in one genome may be mirrored by mutations in the other. Hyobanche and Harveya offer an excellent framework for investigating this phenomenon.