Shedding Light on a Pumpkin Pathogen
Written by Emily Fucarino
Edited by Cindy Ho
Jan 18, 2021
Edited by Cindy Ho
Jan 18, 2021
Cucurbits are members of the gourd family, and include melons, cucumbers, gourds, and a fall favorite—pumpkins. Cucurbits are among the many types of plants susceptible to a powdery mildew disease but are among the most severely affected (Pérez-García et al.). Powdery mildew of cucurbits significantly reduces crop yield and is caused by the fungal plant pathogen Podosphaera xanthii. As an obligate parasite, P. xanthii relies on its host in order to grow and reproduce; and in order to become parasitic, it must first develop fungal structures called haustoria. Haustoria are responsible for transferring plant nutrients to the fungus and for releasing proteins that suppress host defense mechanisms, making them crucial for attaining and sustaining a parasitic state within a host.
The parasitic nature of P. xanthii makes it difficult to culture on media and even more challenging to isolate its haustoria, as they are deeply enmeshed in and surrounded by plant tissue. The barrier that this poses to studying haustoria is significant, because the key role that haustoria plays in pathogenesis makes them prime targets to study in relation to P. xanthii and powdery mildew diseases in general.
Thus, a new approach was developed in order to facilitate a closer examination of the specific processes and proteins involved with the haustoria of P. xanthii. To overcome the intimate association between haustoria and plant matter, researchers infected plants with P. xanthii and used a fluorescent tagging and sorting technique to separate plant, fungal, and haustorial cells from one another, respectively. With the purified sample of haustoria cells that they obtained, researchers were then able to reconstruct probable genetic sequences belonging to the haustoria, including the projected sequence, shape, and function of multiple proteins. This technique also allowed them to identify unique genetic sequences that are found only in haustoria (Polonio et al.), a discovery that can provide new insights into the role of haustoria in fungal plant parasitism.
This approach allowed researchers to more closely examine the mechanisms of pathogenesis of P. xanthii. By incorporating the use of bioinformatics, researchers were able to understand key biological processes, including the role of haustoria in the “protection against reactive oxygen species, the acquisition of different nutrients and genetic regulation mediated by non-coding RNAs” and they found “several secreted proteins expressed exclusively in haustoria such as cell adhesion proteins that have not been related to powdery mildew biology to date.” (Polonio et al).
While this study is specific only to P. xanthii in cucurbits, the developed approach has broad implications for future examinations of haustoria and other powdery mildew-causing fungi. Subsequent findings from this technique have the potential to locate targets for disease control in both P. xanthii and other fungal plant pathogens, making it an important development in powdery mildew research. Unravelling the genetic and biochemical details of haustoria allows researchers to take a closer look at the previously elusive inner workings of pathogenesis in P. xanthii and other plant pathogenic fungi.
Works Cited
Polonio, Álvaro, et al. “The Haustorial Transcriptome of the Cucurbit Pathogen Podosphaera Xanthii Reveals New Insights into the Biotrophy and Pathogenesis of Powdery Mildew Fungi.” BMC Genomics, BioMed Central, 4 July 2019, www.ncbi.nlm.nih.gov/pmc/articles/PMC6611051/.
Pérez-García, Alejandro, et al. “The Powdery Mildew Fungus Podosphaera Fusca (Synonym Podosphaera Xanthii), a Constant Threat to Cucurbits.” Molecular Plant Pathology, Blackwell Publishing Ltd, Mar. 2009, www.ncbi.nlm.nih.gov/pmc/articles/PMC6640438/.