Lu et al. show that diterpenoids contribute to disease resistance in rice. Plant Cell. (2018). https://doi.org/10.1105/tpc.18.00205
Background: Rice (Oryza sativa) is an important food crop. Diseases caused by the fungal blast pathogen Magnaporthe oryzae and bacterial leaf blight pathogen Xanthomonas oryzae cause significant losses. Upon microbial infection plants produce natural products that are assumed to act in defense. Almost all of the many identified antibiotic natural products from rice are diterpenoids that depend on initial cyclization of a general precursor geranylgeranyl diposphate (GGPP) into either syn-CPP, by the enzyme OsCPS4, or ent-CPP, largely by the enzyme OsCPS2. However, the roles of these diterpenoids are unclear.
Question: What are the physiological roles of the natural products derived from these two major pathways of rice diterpenoid metabolism?
Fidings: Rice plants that are either lacking or reduced in the activity of OsCPS2 were more susceptible to M. oryzae and X. oryzae, while lines with additional OsCPS2 enzyme were more resistant to both of these microbial pathogens. By contrast, lines lacking OsCPS4 actually were more resistant to X. oryzae, suggesting that diterpenoids produced from OsCPS4 activity are not associated with resistance to these specific pathogens. Rice plants nevertheless allocate significant metabolic flux towards these natural products. Stimulated by this observation, further analysis was carried out, revealing that these diterpenoids are relevant to non-host disease resistance against Magnaporthe poae, which has adapted to infect wheat (Triticum aestivum) rather than rice.
Next steps: Similar genetic analysis of other enzymes in rice acting in diterpenoid biosynthesis, such as the class I diterpene synthases is anticipated to identify more specific diterpenoid compounds responsible for plant defense against a variety of pathogens. It would also be of interest to examine these enzyme families and diterpenoid classes in wheat.
Lu, Zhang, Brown et al. (2018). Inferring Roles in Defense from Metabolic Allocation of Rice Diterpenoids. Plant Cell May 2018, 30: 1119-1131; DOI: https://doi.org/10.1105/tpc.18.00205