Tea plants arm themselves: two key receptors trigger herbivore defenses

Plants must defend themselves against relentless insect herbivores. A new study uncovers how tea plants (Camellia sinensis), one of the world's most valuable crops, activate their immune defenses at the molecular level. Researchers identified two leucine-rich repeat receptor-like kinases, CsLRR-RLK44 and CsLRR-RLK239, that function as plasma membrane receptors detecting insect attack. These proteins trigger a cascade involving mitogen-activated protein kinases (MPKs), WRKY transcription factors, and jasmonate hormones, ultimately strengthening resistance against the destructive tea geometrid (Ectropis obliqua). By mapping and characterizing 307 receptor-like kinase genes, the study provides the first evidence in woody plants that specific receptors play critical roles in sensing herbivory and initiating defense signaling.

Insect herbivores are a major biotic stress threatening global crop production. Plants perceive attack through elicitors—molecules associated with damage or insect oral secretions—that activate early defense signaling. Previous work in grasses like rice and maize has shown that leucine-rich repeat receptor-like kinases (LRR-RLKs) function as pattern recognition receptors in herbivory perception. Yet their role in woody plants remained largely unknown. Tea plants, frequently damaged by chewing insects such as the tea geometrid, offer an ideal model to explore how LRR-RLKs function in tree species. Due to these challenges, it is necessary to conduct in-depth studies on receptor kinases that initiate herbivory defense in woody crops.

Researchers from the Tea Research Institute, Chinese Academy of Agricultural Sciences, report a new study published (DOI: 10.1093/hr/uhae281) on October 2, 2024, in Horticulture Research. The team systematically analyzed the genome of tea plants and identified two key receptors, CsLRR-RLK44 and CsLRR-RLK239, that are strongly induced during insect feeding. By linking gene expression to resistance traits across tea accessions, and validating through gene-silencing experiments, the scientists demonstrated that these receptors are indispensable for mounting defense responses against the tea geometrid caterpillar.

The study began with genome-wide mining of tea plant sequences, identifying 307 full-length LRR-RLK genes, unevenly distributed across 15 chromosomes. Transcriptome analyses showed that 49 of these genes responded to herbivory, with CsLRR-RLK44 and CsLRR-RLK239 emerging as the strongest candidates for regulating defense. Both genes were rapidly upregulated after caterpillar feeding and correlated negatively with larval growth, indicating a protective role. Subcellular localization confirmed their presence on the plasma membrane, consistent with receptor function. Silencing experiments using antisense oligodeoxynucleotides reduced their expression and significantly increased caterpillar weight gain, highlighting their importance for resistance. Further assays revealed that these receptors regulate downstream defense signaling: silencing reduced the expression of CsMEKK20 and CsMPK3, and impaired induction of key WRKY transcription factors. Crucially, suppression of CsLRR-RLK44 or CsLRR-RLK239 diminished herbivore-induced accumulation of jasmonates and lowered expression of jasmonate biosynthesis genes CsLOX7 and CsAOS. Together, these results establish that the two receptors orchestrate a conserved defense pathway involving mitogen-activated protein kinases (MPKs) cascades, WRKY transcription factors, and jasmonate signaling. The findings extend our understanding of herbivory perception from annual grasses to woody crops of global economic importance.

“Our work demonstrates for the first time that specific LRR-RLKs in woody plants are central to initiating insect defense responses,” said co-corresponding author Dr. Jianyan Huang. “CsLRR-RLK44 and CsLRR-RLK239 act as sentinels on the plasma membrane, detecting herbivory signals and activating canonical defense pathways. This discovery provides valuable genetic targets for improving resistance in tea plants and potentially other woody crops. Beyond tea, it underscores the evolutionary conservation of receptor-mediated defense, opening opportunities to design more resilient plants in the face of increasing pest pressures.”

The identification of CsLRR-RLK44 and CsLRR-RLK239 as key regulators of tea plant immunity offers practical avenues for crop improvement. Breeders can now use these genes as markers to select insect-resistant varieties, reducing reliance on pesticides and promoting sustainable tea cultivation. Insights into receptor-mediated jasmonate signaling also provide strategies for engineering crops with stronger innate immunity. Beyond tea, the research contributes to a broader understanding of how woody plants recognize and respond to herbivory, informing protection of other perennial crops and trees. This knowledge lays the groundwork for innovative approaches to secure agricultural productivity in pest-challenged ecosystems.

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References

DOI

10.1093/hr/uhae281

Original Source URL

https://doi.org/10.1093/hr/uhae281

Funding information

This research was funded by National Natural Science Foundation of China (32372775), Central Public-interest Scientific Institution Basal Research Fund (Y2023PT03), the Zhejiang Science and Technology Major Program on Agricultural New Variety Breeding–Tea Plant (2021C02067), and the Elite Youth Program of Chinese Academy of Agricultural Sciences.

About Horticulture Research

Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.