The microRNA-7322-5p/p38/Hsp19 axis modulates Chilo suppressalis cell-defences against Cry1Ca: An effective target for a stacked transgenic rice approach

Authors: WU, YAN - Huazhong Agricultural University; WENG, ZIIIN - Huazhong Agricultural University; YAN, HAIXIA - Huazhong Agricultural University; YAO, ZHUOTIAN - Huazhong Agricultural University; LI, ZHENZHEN - Huazhong Agricultural University; SUN, YAJIE - Huazhong Agricultural University; MA, KANGSHENG - Huazhong Agricultural University; Hull, Joe; ZHANG, DELIN - Huazhong Agricultural University; MA, WEIHUA - Huazhong Agricultural University; HUA, HONGXIA - Huazhong Agricultural University; LIN, YONGJUN - Huazhong Agricultural University

Submitted to: Nature Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2023
Publication Date: 8/21/2023
Citation: Wu, Y., Weng, Z., Yan, H., Yao, Z., Li, Z., Sun, Y., Ma, K., Hull, J.J., Zhang, D., Ma, W., Hua, H., Lin, Y. 2023. The microRNA-7322-5p/p38/Hsp19 axis modulates Chilo suppressalis cell-defences against Cry1Ca: An effective target for a stacked transgenic rice approach. Nature Microbiology . 21(9):1827-1838. https://doi.org/10.1111/pbi.14095.
DOI: https://doi.org/10.1111/pbi.14095

Interpretive Summary: For many bacterial pathogens of invertebrates, pore-forming toxins are important factors in infection and pathogenesis. Bacillus thuringiensis (Bt) is one such bacteria that produces a number of protein toxins, such as the crystal proteins (Cry), that are lethal to many families of insect pests, but that have little impact on beneficial arthropods and the environment. As such, Cry protein toxins have been widely developed for pest management with significant research focused on the molecular mechanisms that trigger lytic pore formation in response to their interactions with host cell membrane receptors. Less is known about the responses of pests in response to the Cry toxin. To address this knowledge deficit, molecular and cellular studies were conducted using the striped rice stemborer (Chilo suppressalis), a major pest in rice crops. Cry toxin exposure was found to activate a microRNA (miRNA) dependent phosphorylation cascade that triggered the activation of a small heat shock protein (sHsp) family member. Reducing the levels of the sHsp resulted in higher larval mortality after Cry toxin exposure, suggesting that the sHsp plays a critical role in the cellular response to the toxin. Interactions between the sHsp and the Cry toxin suggest a potential sequestration-based defense mechanism. Targeted disruption of the cellular pathway identified in this study could thus negatively impact the pest’s defenses and thus increase the overall efficacy of Cry toxins.

Technical Abstract: Bacillus thuringiensis (Bt)-secreted crystal (Cry) toxins form oligomeric pores in host cell membranes and are a common element in generating insect-resistant transgenic crops. Although Cry toxin function has been well documented, cellular defenses against pore-formation have not been as well developed. Elucidation of the processes underlying this defense, however, could contribute to the development of enhanced Bt crops. Here, we demonstrate that Cry1Ca-mediated downregulation of microRNA-7322-5p (miR-7322-5p), which binds to the 3’ untranslated region of p38, negatively regulates the susceptibility of Chilo suppressalis to Cry1Ca. Moreover, Cry1Ca exposure enhanced phosphorylation of Hsp19, and hsp19 downregulation increased susceptibility to Cry1Ca. Further, Hsp19 phosphorylation occurs downstream of p38, and pull-down assays confirmed the interactions between Hsp19 and Cry1Ca, suggesting that activation of Hsp19 by the miR-7322-5p/p38/Hsp19 pathway promotes Cry1Ca sequestration. To assess the efficacy of targeting this pathway in planta, double-stranded RNA (dsRNA) targeting C. suppressalis p38 (dsp38) was introduced into a previously generated cry1Ca-expressing rice line (1CH1-2) to yield a single-copy cry1Ca/dsp38 rice line (p38-rice). Feeding on this rice line triggered a significant reduction in C. suppressalis p38 expression and the line was more resistant to C. suppressalis than 1CH1-2 in both short term (7-day) and continuous feeding bioassays as well as field trials. These findings provide new insights into invertebrate epithelium cellular defenses and demonstrate a potential new pyramiding strategy for Bt crops.