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

Harveya钩。是一种寄生植物属，原产于南非。哈维尔花通过一种叫做吸器的特殊根器官寄生在其他植物上。关于Harveya物种的划分，物种之间的关系，或者Harveya物种是否特定于特定的寄主植物，我们知之甚少。本研究的目的包括检查形态特征以确定种界，从形态特征和DNA序列推断系统发育历史，以及通过挖掘吸器确定寄主特异性。在寄生植物中，编码光合蛋白的基因不受功能限制。这些基因可能发生功能降低的突变。由于寄生植物从寄主植物而不是通过光合作用获取营养，这些突变对适应性没有损害。因此，这些突变可能会遗传给后代，并在种群中固定下来。光合作用基因的退化或缺失已在不同谱系的寄生植物中得到证实。另一种寄生虫，hyobche L.，是Harveya的姐妹属。土狼的rbcL基因发生了突变，rbcL是一种叶绿体基因，编码Rubisco的大亚基，Rubisco是光合作用所必需的蛋白质。这些突变使rbcL在该属中失去功能。人们可能会期望Harveya在这个基因中展示类似的功能终止突变。然而，到目前为止，在所有的哈维亚物种中，rbcL编码一种功能性蛋白。有两种假设可以用来解释这些突变的缺失。(a)在Harveya和Hyobanche中Rubisco功能的丧失是通过不同的途径发生的。(b) Rubisco在Harveya中保留了兼性光合作用或未知的非光合作用的功能。在本研究中，我们将在Hyobanche和Harveya中对编码小亚基（rbc）和大亚基（rbcL）的基因进行测序，以比较其功能。此外，这些基因的RNA和蛋白质产物将被分析，以确定Rubisco功能在这些属中丧失的进化途径，或者Rubisco是否具有一些非光合作用。这项研究的重要性是多方面的。在同等大小的温带地区中，南非保持着最大的花卉多样性。然而，随着人口的持续增长和人类栖息地向野生地区的扩张，许多物种可能会濒临灭绝。保护工作将依赖于对受威胁生物的进化史和生态需求（例如合适的植物宿主）的了解。其次，hyobche和Harveya中rbcL功能的二分法为研究非光合植物光合基因的进化提供了一个理想的系统。此外，rbcL和红细胞具有整合的功能，但编码在植物的不同基因组中：rbcL在叶绿体基因组中，而红细胞在细胞核中。其中一个基因功能的丧失可能导致另一个基因功能的丧失。到目前为止，还没有研究检验一个基因组中发生的突变是否会被另一个基因组中的突变所反映。Hyobanche和Harveya为研究这一现象提供了一个极好的框架。

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.