Zhenlong Xing: Plants may exploit herbivore-induced flavonoids to regulate AM fungal symbiosis 

Zhenlong Xing: Plants may exploit herbivore-induced flavonoids to regulate AM fungal symbiosis 

In our latest post, Zhenlong Xing—a researcher at Henan University, Kaifeng, China—presents his work ‘Foliar herbivory modifies arbuscular mycorrhizal fungal colonization likely through altering root flavonoids’. He discusses the inspiration behind this paper and the path he took to become an ecologist. 

About the paper 

In June 2018, I obtained my PhD degree and I was lucky to start my new research career in Jianqing Ding’s Lab at Henan University. Previous work in his lab has focused on interactions between above- and below-ground herbivorous insects. They found that insect herbivory can trigger changes in tannins and flavonoids in both Chinese tallow tree leaves and roots that facilitate conspecific and heterospecific herbivore interactions, and thus help maintain insect community stability (Huang et al. 2013, Proc. R. Soc. B., 280: 20131318; Huang et al. 2014, Nat. Commun., 5: 4851). It is well known that tannins are important metabolites that defend plants against insect attackers. However, the multiple roles of herbivore-modified root flavonoids had not been identified. 

I began my research on the relationship between insect herbivores and plant-colonizing microbes, especially mycorrhizal fungi, after I joined Jianqing Ding’s team. Terrestrial plants have been attacked by insect herbivores for ca. 350 million years, and mycorrhizal fungi have colonized nearly 90% of terrestrial plants for ca. 400 million years. Consequently, land plant-mediated interactions between insect herbivores and mycorrhizal fungi have been occurring for hundreds of million years. Plants can increase mycorrhizal colonization following low levels of herbivory, and decrease colonization under higher herbivory intensity, but the mechanisms remained unclear. Given that flavonoids can promote arbuscular mycorrhizal (AM) fungal colonization, and given that the undefined herbivore-induced flavonoids role in Chinese tallow, I worked with a master’s student, Tiantian Ma, to explore how insect herbivory affects AM fungal colonization of tallow roots by altering plant metabolites. 

Tiantian Ma, now working at a senior high school (left), and the tallow seedlings we prepared for common garden experiments (right) (credit: Tiantian Ma) 

There are two main findings in our study. First, utilizing four insect herbivore species, we confirmed that AM fungal colonization was promoted by light herbivory but suppressed by heavy herbivory. Second, flavonoids in roots and root exudates, rather than carbon content, were associated with AM fungal symbiosis responses to foliar herbivory. Previous studies showed that insect herbivores and AM fungi interact primarily through their competition for host plant photosynthates (of which AM fungi consume up to 20%). Our study is the first to report the roles of herbivore-induced secondary compounds (flavonoids) in modulating AM symbiosis responses to insect herbivory, providing new insights into our understanding of insect-plant-AM fungi interactions. 

Foliar insect herbivores used in this study: Spodoptera litura (credit: Tiantian Ma), S. frugiperda (credit: Limei He), Cnidocampa flavesvens (credit: Dingli Wang), and Bikasha collaris (credit: Tiantian Ma) 

About the research 

Understanding the mechanisms underpinning interactions between insect herbivores and plant-associated microbes is critical for plant health. My study explores how insect herbivory affects root-colonized AM fungi. This paper suggests that root flavonoids may play an important role in shaping AM fungal colonization responses to foliar herbivory. Studying the underlying mechanisms between insect herbivores and AM fungi may help to explain how plants simultaneously cope with antagonists and mutualists during their long co-evolutionary history. 

The biggest challenge in this study was we could not obtain enough herbivorous insects at the same time, so the experiments were conducted at different times over 1 year. Here I would like to give very special thanks to our collaborator Evan Siemann. During Covid when in-person international collaboration was not possible, we discussed the paper and the data with WeChat and E-mail many times. During the revision of the manuscript when we were all able to be together in Kaifeng, we re-analyzed the data and revised the paper from dawn to dusk over several days. 

Jianqing Ding (front left), Evan Siemann (front right), and some members of our team (credit: Zhenlong Xing)

This study is just an initial attempt to address the role of herbivory-induced secondary compounds in affecting AM fungal colonization. I am now working on a wide range of plant compounds and utilizing more plant-herbivore systems to better understand the mechanisms behind insect-plant-AM fungi interactions. For example, we recently found that the enhancement of mycorrhizae after herbivory was associated with increased levels of fatty acids (in revision at Journal of Ecology). I think it is very interesting to dig deep into the mechanisms regulate insect-plant-microbe interactions. 

About The Author 

Zhenlong Xing, Lecturer at Henan University, graduated from the Chinese Academy of Agricultural Sciences and China Agriculture University (credit: Zhenlong Xing) 

I grew up on a small village in China and trained with conventional farmer skills during my childhood. I love nature and I have a strong curiosity about soils, plants and insects. Hence, I entered an Agricultural University with a major in entomology. After I graduated from university, in 2011, I went to Beijing to explore the mechanistic basis of migratory insects under the supervision of Kongming Wu, current president of the Chinese Academy of Agricultural Sciences (CAAS). Three year later, I continued studying invasive insect species at CAAS and China Agricultural University (CAU) under the supervision of Zhongren Lei and Wanzhi Cai. After I received my PhD degree, in 2018, I recognized that entomology is only a part of the natural world, and my research interest turned to ecology. 

I am currently an ecology researcher at Henan University. This study is my first paper published in an ‘ecology’ journal. It is very important to me and encourages me to become an ecologist. The past 5 years has been a difficult time in my research career. I was not successful in my applications to the NSFC (National Science Foundation of China) for young scholars from 2019 to 2022 because I changed my research focus from entomology to ecology. Fortunately, my application was successful in 2023, my last opportunity. My advice to aspiring young ecology researchers is therefore: to stay calm and relaxed, to retain belief, and to concentrate on the aspects of nature that inspire them.  

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