Molecular mechanisms of dormancy and germination in parasitic and non-parasitic plants

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One of the major impediments to food security in Africa is infestation caused by a parasitic plant called Striga hermonthica. Striga parasitizes major food crops like sorghum, rice and millet, which results in 30 to 100% yield losses for over 100 million subsistence farmers. As an obligate hemiparasitic plant, Striga cannot survive on its own and relies on infecting a plant host in order to obtain nutrients, water and assimilates. It is essential that Striga seed “wake up” (germinate) and begin growing only when a potential host is nearby. As a result, Striga has evolved unique strategies that are distinct from non-parasitic plants. For example, seeds typically germinate in response to light and plant hormones like gibberellic acid (GA). Striga, however, does not respond to these signals. Instead, Striga seeds wake up upon detecting a class of plant hormones called strigolactones (SL). This chemical signal is released into the soil by plant hosts to promote a beneficial interaction with fungi. Striga's dependence on host-derived SLs is a weakness that can be exploited for the development of technologies to combat Striga infestations. This will require a detailed mechanistic understanding of how Striga seeds use SL as a “wake up” signal in the soil. Not surprisingly, there are many signals that affect the seed's decision to germinate. Seeds have to integrate all of this information and translate it into gene expression. Certain combinations of gene expression make up a “germination code” to instruct a seed whether or not to wake up. In many ways, Striga has rewired this germination code because of its dependence on SLs, rather than environmental cues, to trigger germination. The Lumba Lab will determine how Striga has rewired the code by combining cutting-edge approaches such as transcriptomics and large-scale protein interaction studies. During my post-doc, I successfully applied these methods to construct protein interaction networks in Arabidopsis thaliana. Our approach will identify components that are important for germination in Striga and examine how these components interact based on high-throughput yeast two-hybrid methods. My group will apply systems biology approaches to build signalling networks which will reveal how various signals converge to form the germination code. To understand the evolution of the code, we will construct networks of Striga and Arabidopsis components. Comparing these networks will reveal protein interactions that have been gained or lost by Striga, which will provide insight about the evolution of Striga's parasitic lifestyle. Significance: Despite the devastating effects of Striga on 100 million people, molecular mechanisms underlying germination in parasitic plants are largely unknown. Elucidating these mechanisms, not only will answer fundamental evolutionary questions in biology but also lead to solutions in combating the scourge of Striga.