The more we learn about living things, the more complex they seem. New discover to have gained speed with the unfolding of molecular genetics and the understanding that most biological functions are determined by the order of chemicals that make up our DNA. Many features of this complexity continue to baffle us: Why should we clever humans have around three million pairs of these DNA chemicals when the “simple” tea plant we cultivate for our pleasure has about a million more?
Pelly Malebe’s curiosity as a young child inclined her toward questions like this, and she realized early that the answers to many of those questions about how life “works” could be found in her school books, especially those explaining biology, and, when she was a little older, genetics. She was drawn to the challenge of understanding the most intricate structures of living systems, and then of how they worked.
Today as a young adult and member of RISE-SABINA, she is even more deeply involved in such questions. Under the guidance of Professors Zeno Apostolides and Zander Myburg, she is pursuing her PhD in the University of Pretoria’s biochemistry department, where she has become adept at the advanced technologies used to identify, quantify, and replicate the DNA-based genes of organisms. One of her most useful tools is a biochemical technology called the polymerase chain reaction (PCR), by which she has learned to amplify copies of particular DNA sequences, each of which may include one or more fragments of genes.
Because of the department’s longstanding work on the biochemistry of the tea plant, Camellia sinensis, Pelly has joined in the same pursuit – specifically in exploring the genetic makeup of tea in hopes of identifying new drought-resistant varieties, which are urgently needed in dry southern Africa. Whether or not the African climate changes in the direction of lower rainfall, as many scientists have predicted, drought has long been a barrier to the production of tea crops. In fact, there is a strong correlation between some of the most popular strains, or cultivars, of tea and a low tolerance for even moderate degrees of drought.
When tea plants are faced with a period of light rainfall, they use a number of tactics to survive:
• Dropping leaves
• Closing the stomata of the leaves, which slows or blocks photosynthesis
• Constricting the main stem, which reduces plant function
• Accumulating starch in the roots, a survival measure stimulated by harsh conditions
• Superoxide dismutase (detoxifying)
Virtually all of these tactics reduce the tea plant’s value as a commercial crop. These tactics, like virtually every aspect of the plant’s life, are determined by the complex tea genome, or genetic makeup, which is the frontier Pelly is exploring. In particular, she is seeking techniques to protect tea plants against drought that do not also reduce its ability to produce tasty tea. Even more desirable are drought-resistant, desirable cultivars that also have genes that can resist multiple pests and respond to cultivation in other positive ways.
Knowing that DNA composition varies among different cultivars, and that these molecular differences can now be detected by laboratory technologies, she has painstakingly learned modern techniques for searching out the distinctive patterns or molecular “markers” for such behaviors, beginning with drought tolerance. She is also alert for markers that indicate other desirable traits and that may be molecular neighbors of the drought tolerance markers. In this way, she hopes that the tea plant will offer signals that allow the tea grower to take advantage of any number of plant behaviors that bring advantages to the grower – and sipper.
Like other plant research, Pelly’s study of tea relies on a close partnership between researchers in the lab and those in the field. One advantage of RISE is that such partnerships are often easy to arrange. In the case of tea, Pelly has been collaborating for several years with Nick Mphangwe of Malawi, who has already earned his PhD at the University of Pretoria and now spends most of his time at the Tea Research Foundation of Central Africa’s center in Malawi. At TRFCA, cultivars that show good drought resistance are identified in the field. DNA samples are then harvested from those particular plants and transported to the Pretoria lab for genetic analysis. In addition to Nick’s field work in Malawi, Pelly also makes use of the university’s own smaller tea fields at the University of Pretoria, where the traits of these and other cultivars are studied.
Since beginning her master’s work in the RISE program, Pelly has pinpointed a section of tea DNA that is associated with drought tolerance. This section, which is 1200 base pairs long, is identified in the lab with the help of a process called electrophoresis (electro plus migration). The process begins with the preparation of agarose, one of the components of agar, a valuable component of algae that is harvested along the beaches in Tanzania, Kenya, and elsewhere (and studied in the WIO-RISE network). To make this gel, the agarose is extracted from the agar, dried to a powder, mixed with hot water, and cooled. When the agarose gel is cut into slabs, mixtures of DNA, RNA, and other large molecules can be placed on it and made to move, or “migrate,” through the gel matrix by application of an electrical field. Because small fragments move faster than large ones, the fragments can be identified according to their size, with those of the same length gathering as distinct visible “bands” in the gel. The formation of a band of fragments matching the length of the marker for drought resistance tells the geneticist that this plant is drought-resistant; the marker does not appear in drought-susceptible cultivars.
For her work in developing a method for screening tea cultivars for drought tolerance, completed during her MSc studies, Pelly and Prof. Apostolides were awarded a provisional patent. The potential outputs of their work are robust molecular markers that can be used in a selection process to improve tea yields throughout the global tea industry. Pelly’s focus is on increasing the understanding of the genetic basis of drought tolerance in plants, which may lead to other drought-tolerant crop varieties and thus to improved food and job security.
The final filing of the patent is underway with the African Regional Intellectual Property Organization, and also in India, Sri Lanka, China and South Africa, other leading tea producers. According to the wording of the patent application, the techniques developed at Pretoria include “the steps for providing plant material to be screened; extracting genomic DNA from the plant materials; and selectively amplifying the portion of the genomic DNA coding for drought tolerance.”
In the future, Pelly has several objectives. The first is developing the use of genetic markers for decision making and for conserving the crop plant germ plasm. Another is to develop marker-assisted selection for drought tolerance, yield, and quality, all of which have great potential value for the tea breeding industry. Finally, she hopes to use marker data to find associations with other traits of economic importance, which “may be useful to tea breeders world-wide.”
Pelly has already received much recognition for her work. As a bachelor’s student in human genetics and a master’s student in biotechnology, she was employed by the University of Pretoria as a teaching assistant, and elected to membership in the Golden Key International Honor Society. After she began her PhD work at Pretoria, she was funded not only by RISE through SABINA, but also by the South African National Research Foundation’s Innovation Doctoral Scholarship.
In addition, she was given a South African Women in Science Award (WISA) by the Department of Science and Technology. This award was created to recognize and reward the achievements of women scientists and researchers in South Africa, and also to dispel the myth that science is for men only. The DST hopes that the achievements of the award winners will encourage other women to persevere in overcoming gender discrimination to contribute to research and knowledge generation.
Story: Alan Anderson, Science Initiative Group, Blog posts, December 2013