A battle in rice flowers

Li et al. investigate the mechanisms of defense and counter-defense in a floral pathosystem.


By Guo-Bang Li, Wen-Ming Wang, and Jing Fan

Background: Rice false smut is an emerging fungal disease threatening rice production worldwide. This disease not only reduces grain yield but also introduces food toxins. The causative pathogen invades rice flowers via the gap between the two bracts (lemma and palea) enclosing the floret and specifically infects the stamens and pistils. The underlying mechanisms by which rice flowers defend against the pathogen and the pathogen counteracts this defense remain largely unknown.

Question: The optimal defense theory predicts that flowers should receive protection from constitutive defenses, rather than inducible defenses against herbivores. Do rice flowers deploy constitutive or induced defense against the false smut fungus? How does the pathogen overcome rice defense?

Findings: Chitin is a vital component of fungal cell walls and often elicits plant immunity. We show that rice flowers predominantly employ chitin-induced immunity against the false smut fungus in lemmas and paleas, rather than in stamens and pistils. We identify a secreted protein, named UvGH18.1, as a core virulence factor for the false smut pathogen. UvGH18.1 breaks down chitin to prevent host immune elicitation and further targets rice chitin sensors to impair chitin signaling, suppressing host immunity exerted at lemmas and paleas to gain access to stamens and pistils. Conversely, pretreating flowers with chitin promotes rice resistance to false smut, offering a potential strategy to control this disease.

Next steps: One next step is to identify plant receptors that recognize UvGH18.1 or other molecules derived from the false smut fungus. Another is to identify chemicals that inhibit UvGH18.1 function to block pathogen infection.


Guo-Bang Li, Jie Liu, Jia-Xue He, Gao-Meng Li, Ya-Dan Zhao, Xiao-Ling Liu, Xiao-Hong Hu, Xin Zhang, Jin-Long Wu, Shuai Shen, Xin-Xian Liu, Yong Zhu, Feng He, Han Gao, He Wang, Jing-Hao Zhao, Yan Li, Fu Huang, Yan-Yan Huang, Zhi-Xue Zhao, Ji-Wei Zhang, Shi-Xin Zhou, Yun-Peng Ji, Mei Pu, Min He, Xuewei Chen, Jing Wang, Weitao Li, Xian-Jun Wu, Yuese Ning, Wenxian Sun, Zheng-Jun Xu, Wen-Ming Wang, Jing Fan (2024). Rice false smut virulence protein subverts host chitin perception and signaling at lemma and palea for floral infection. https://doi.org/10.1093/plcell/koae027