RNA Messages Cross Kingdom Boundaries, Opening a New Era of Chemical-Free Crop Protection

Plants and microbes are talking to each other in a language scientists are only beginning to translate, and the words are made of RNA. A comprehensive review published in the journal Stress Biology synthesizes a decade of discoveries showing that small RNA molecules travel across the boundaries of biological kingdoms, silencing genes in organisms far removed from the cells that produced them. This phenomenon, known as cross-kingdom RNA communication, is now being harnessed to build a new generation of crop protection tools that could replace chemical pesticides with precisely targeted, biodegradable molecules.

The core of the story lies in RNA interference, or RNAi, a gene-regulation system shared across much of life. Small interfering RNAs and microRNAs can be loaded into Argonaute proteins to form silencing complexes that seek out and destroy matching messenger RNAs. What has stunned researchers is that these molecules do not respect species barriers. A fungal pathogen can ship its own small RNAs into a plant cell, where they hijack the host’s Argonaute machinery and switch off immunity genes. Conversely, a plant can package its small RNAs into extracellular vesicles and send them into an invading fungus, where they silence the very genes the pathogen needs to cause disease.

The evidence is strikingly specific. The gray mold fungus Botrytis cinerea secretes small RNAs such as Bc-siR3.1 and Bc-siR5 into plant cells, where they co-opt the host AGO1 complex to suppress immunity-related genes. The wheat rust pathogen Puccinia striiformis delivers a microRNA-like RNA called Pst-milR1 that silences PR2, a gene encoding beta-1,3-glucanase involved in degrading fungal cell walls. In the banana-wilting Fusarium oxysporum system, fungal milRNAs target banana transcription factors and receptor-like kinases, dismantling early defense signaling. Rhizoctonia solani deploys a battery of milRNAs against rice, suppressing vacuolar sorting receptors, NB-ARC immune receptors, and F-box proteins to blunt the hypersensitive response. Even Valsa mali, the apple canker pathogen, uses a single milRNA to silence two receptor-like kinases and reduce reactive oxygen accumulation and callose deposition in host tissue.

Crucially, the traffic runs both ways. Plants selectively load small RNAs into extracellular vesicles with the help of RNA-binding proteins including AGO1, the helicases RH11 and RH37, and the annexins ANN1 and ANN2, which sort, stabilize, and transport the cargo. Encapsulation shields the RNA from extracellular nucleases during the journey. In the Brachypodium distachyon and Fusarium graminearum system, researchers identified 258 plant-derived small RNAs that target fungal messenger RNAs and significantly reduce pathogenicity. Wheat roots even send microRNAs into the beneficial fungus Clonostachys rosea, where they fine-tune fungal secondary metabolism rather than triggering defense, showing that RNA exchange also shapes cooperative relationships, not just conflict.

Bacteria play this game too, though the evidence is younger. The rice pathogen Xanthomonas oryzae pv. oryzicola packages a small RNA called Xosr001 into outer membrane vesicles, which deliver it into rice cells to silence OsJMT1, a jasmonate metabolism gene, thereby suppressing stomatal immunity. In the opposite direction, Arabidopsis plants have been shown to silence virulence genes of Pseudomonas syringae, reducing bacterial colonization and impairing stomatal reopening, with the silencing RNAs exported through both vesicle-associated and non-vesicular routes. Plant-derived small RNAs can also suppress gene expression in Ralstonia pseudosolanacearum, the agent of bacterial wilt. Even mutualistic partnerships show RNA crosstalk: Bradyrhizobium japonicum produces tRNA-derived fragments that accumulate in soybean nodules and use the host AGO1 machinery to regulate plant transcripts involved in nodulation.

Viruses occupy a special place in this landscape. Because viral RNA replicates continuously inside host cells, the review’s authors treat plant-virus systems as a closely related but mechanistically distinct model rather than classical cross-kingdom transfer. Still, the dynamics are instructive. Plants process viral double-stranded RNA with Dicer-like enzymes into virus-derived small interfering RNAs that guide sequence-specific degradation of viral genomes. Viruses fight back with silencing suppressor proteins such as the NS3 protein of Rice stripe virus, which binds small RNAs and interferes with microRNA biogenesis. Virus-derived siRNAs from Rice black-streaked dwarf virus directly target host genes in rice and maize, while virally activated siRNAs extend RNA regulation to endogenous plant transcripts during infection, creating layered, bidirectional control networks.

These discoveries have crystallized into three agricultural technologies that share a common RNAi mechanism but differ in delivery. Spray-induced gene silencing, or SIGS, applies double-stranded RNAs directly onto plant surfaces, where they are taken up by tissues and silence invading pathogens. It is non-transgenic, rapid, and flexible, and has been shown to suppress gray mold, Fusarium head blight, stem rot, powdery mildew, and late blight across cereals, vegetables, fruits, and ornamentals. Artificial vesicles and nanocarriers such as layered double-hydroxide nanosheets dramatically extend the persistence of sprayed RNAs, with encapsulated double-stranded RNAs protecting tomato and grape tissues for up to ten days and grape leaves for up to twenty-one days.

Host-induced gene silencing, or HIGS, takes the opposite approach: the plant itself is genetically engineered to continuously produce silencing RNAs directed at pathogen genes. Stable HIGS lines have delivered durable resistance in sugarcane against Pokkah boeng and smut, in rice against Bakanae disease and blast, in potato against late blight, and in apple against ring rot. In one notable strategy, transgenic Arabidopsis expressing short tandem target mimics effectively blocked the immune-suppressing small RNAs of Botrytis cinerea, reducing gray mold infection. HIGS offers long-lasting, tissue-specific protection, but it inherits the regulatory hurdles, biosafety debates, and public concerns that surround genetically modified crops, and it demands years of development time.

The newest and perhaps most intriguing strategy is microbe-induced gene silencing, or MIGS, which recruits beneficial microorganisms as living RNA delivery vehicles. Engineered Trichoderma harzianum strains colonizing the rhizosphere produce small RNAs that silence virulence genes in Verticillium dahliae and Fusarium oxysporum. Even more remarkably, engineered Bacillus subtilis and Pseudomonas putida can package double-stranded RNAs into extracellular vesicles and deliver them across kingdoms to fungal pathogens, suppressing Botrytis and Verticillium infections in Arabidopsis and tomato. Because microbes protect their RNA cargo from environmental degradation and can be produced at relatively low cost, MIGS could overcome the two biggest weaknesses of sprayed RNA: instability and expense.

The field is moving from laboratory proof-of-concept toward commercial reality. RNA-based pesticides are a rapidly growing industry, and China has officially released the first batch of registered RNA pesticide products, targeting Tobacco Mosaic Virus. The review argues that the safest and most effective targets will come from cross-kingdom small RNAs themselves, molecules already filtered through millions of years of co-evolution, whose natural trafficking suggests low off-target risk and environmental compatibility. Pairing these evolutionarily optimized sequences with microbial bio-factories for production and delivery, the authors contend, could dissolve the techno-economic barriers that have slowed RNA biopesticides. Significant questions remain, including how RNAs are packaged and recognized by recipient cells, how stable they are under field conditions, and what ecological effects engineered microbes might have on soil biodiversity. But the direction is clear: the quiet molecular conversation between plants and microbes is becoming a blueprint for agriculture that protects crops with the precision of a key in a lock rather than the blunt force of a chemical spray.

Subject of Research: Cross-kingdom RNA communication between plants and microbes and its application in RNA interference-based crop protection

Article Title: Cross-kingdom RNA in plant–microbe interactions: from molecular interactions to next-generation crop protection

Article References: Cross-kingdom RNA in plant–microbe interactions: from molecular interactions to next-generation crop protection. (n.d.). https://doi.org/10.1007/s44154-026-00337-x

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00337-x

Keywords: cross-kingdom RNA, RNA interference, plant-microbe interactions, spray-induced gene silencing, host-induced gene silencing, microbe-induced gene silencing, small RNAs, extracellular vesicles, RNA pesticides, fungal pathogens, plant immunity, sustainable agriculture