Targeting TaNSUN2 provides a potential route to combine antiviral resistance with improved productivity in wheat

Abstract

Research on crop disease has shifted from a single pathogen-host framework toward a multifactorial host-microbiota-environment framework. This transition, captured by the pathobiome concept, redirects attention from individual pathogens to the broader biological networks that condition disease establishment, progression, and outcome [1].In plants, disease can therefore be considered within a microbiota-aware framework in which pathogen success is shaped by host genotype, environment, and surrounding microbial consortia, including their ecological reassembly during infection.Within this broader context, host susceptibility factors are important because they can influence pathogen fitness as well as the infection-prone physiological state of the host.TaNSUN2 as a host factor co-opted by Chinese wheat mosaic virus (CWMV), and show that weakening this dependency enhances antiviral resistance while improving yieldrelated traits [2]. The study motivates two linked questions: how does CWMV redirect TaNSUN2 to control viral RNA fate, and can homoeolog-specific perturbation reduce this dependency without imposing a productivity penalty? The working hypothesis developed here is that a discrete TaeEF1A-TaNSUN2 recruitment module, rather than the entirety of TaNSUN2 function, constitutes a tractable susceptibility node. From a pathobiome-aware perspective, this is a virus-exploited epitranscriptomic hostdependency module; however, the study does not directly demonstrate restructuring of the wider pathobiome.CWMV is a soil-borne, bipartite positive-sense RNA furovirus that infects wheat and is transmitted to roots by the obligate plasmodiophorid Polymyxa graminis [3]. Infection produces chlorotic mosaic symptoms and stunting in winter wheat, while long-lived vector resting spores make eradication from infested soil difficult. Resistant cultivars therefore remain the most practical management option, which gives particular agricultural relevance to host susceptibility factors that can be modified without compromising yield.RNA modifications are central post-transcriptional regulators of RNA metabolism and gene expression in eukaryotes [4]. Among them, m5C influences RNA stability, export, translation, and stress adaptation [5; 6]. Chemically, m5C is installed by S-adenosyl-Lmethionine-dependent RNA cytosine-5 methyltransferases through a conserved catalytic cysteine and a covalent enzyme-RNA intermediate [5; 6]. In mammals, NSUN2 is a major mRNA m5C writer, whereas ALYREF and YBX1 recognize or bind m5C-modified transcripts to regulate export and stability [7; 8]. In plants, transcriptome-wide analyses have detected m5C in coding and noncoding RNAs and linked it to development and environmental responses. In Arabidopsis, TRM4B functions as an RNA m5C writer; trm4b mutants show reduced m5C, altered stability of target transcripts, and root-development defects [9]. In rice, OsNSUN2 maintains mRNA m5C methylation and supports growth under elevated temperature [10]. Plant m5C readers and erasers remain less completely defined, and it was unclear whether a virus could redirect a host m5C writer to viral RNA and whether such exploitation could be disrupted without an agronomic penalty.Plant-virus epitranscriptomics has so far been shaped largely by studies of N6methyladenosine (m6A), which can have opposing effects in different virus-host combinations. In Arabidopsis, the m6A demethylase ALKBH9B promotes alfalfa mosaic virus infection and vascular movement [11; 12], whereas YTH-domain ECT proteins recognize m6A-marked viral RNA and contribute to antiviral restriction [13].In wheat, TaHAKAI has context-dependent functions during wheat yellow mosaic virus infection: its m6A-writer activity can favor viral RNA accumulation, while its E3-ligase activity promotes degradation of a viral silencing suppressor and is linked to favorable spike traits [14]. Recent tomato profiling further showed that tomato spotted wilt virus reshapes the host m5C landscape and that SlTRM4B stabilizes defense-related host transcripts [15]. These comparisons underscore that the outcome of an RNA modification depends on the modified substrate, the reader or effector recruited, and the viral context. The TaNSUN2 study is distinctive because it directly links m5C deposition on viral RNA with homoeolog-specific functional differentiation and favorable agronomic consequences.Jiang et al. address this unresolved m5C question directly. CWMV does not appear to recruit TaNSUN2 on its own; instead, it co-opts the host translation elongation factor TaeEF1A, which recruits TaNSUN2 to viral replication complexes (VRCs). Within VRCs, TaNSUN2 deposits m5C on viral RNAs, increasing RNA stability and translational efficiency. m5C deposition in the viral 3′ untranslated region has two complementary effects: it strengthens the association of TaeEF1A with viral RNA to support replication and enhances coat-protein binding to promote virion assembly. Thus, CWMV repurposes host m5C machinery at multiple stages of infection, providing a direct example of viral exploitation of an epitranscriptomic regulator.A particularly important aspect of the study is that resistance arises by weakening a defined host-virus molecular interface rather than by eliminating all TaNSUN2 activity. Natural allelic variation in TaNSUN2 reduces its affinity for TaeEF1A, thereby limiting recruitment to viral replication complexes and attenuating proviral activity without broadly disrupting host RNA metabolism. This distinction matters because resistance may be achieved not only by knocking out susceptibility genes, but also by selectively disrupting the pathogen-dependent interaction while preserving endogenous functions. This principle aligns with a broader trend in plant disease biology: host dependency often resides in discrete molecular interfaces rather than in the entirety of a host protein's physiological role. The susceptibility-gene framework likewise emphasizes that loss or modification of host compatibility factors can provide resistance, while pleiotropic effects must be evaluated case by case [16; 17]. TaNSUN2 is therefore especially relevant to breeding because naturally occurring or engineered variants could preserve core endogenous functions while diminishing pathogen exploitation. A related principle is illustrated by the Rice grassy stunt virus (RGSV) P3-D14/SL pathway, in which infection depends on a specific interaction with a host hormone receptor to hijack strigolactone signaling and suppress antiviral RNA interference [18]. Precise modification of this interaction interface can confer robust resistance without substantial growth or yield penalties.Particularly noteworthy is the agronomic outcome of perturbing TaNSUN2. Jiang et al.report that knockout of TaNSUN2-5A markedly enhances CWMV resistance, increases thousand-grain weight by approximately 5.9 g, improves grain length and width, and raises yield per plant by more than 14%. Under the genetic background and conditions examined, enhanced antiviral resistance therefore did not require a detectable productivity trade-off. This result supports a cautious interpretation: TaNSUN2-5A is a promising route for combining resistance with favorable yield-related traits, although it does not yet establish a general mechanistic uncoupling of susceptibility from productivity.One plausible explanation for this favorable outcome is homoeolog specialization.Because the three TaNSUN2 copies are not functionally equivalent, selective perturbation of TaNSUN2-5A may strengthen antiviral defense while the other copies retain essential endogenous functions. Polyploid redundancy therefore becomes an opportunity for allele-specific or copy-specific intervention rather than only an obstacle to genotype-phenotype analysis. Such subfunctionalization could buffer developmental costs and permit finer adjustment than would be possible in a single-copy system.Nevertheless, the causal contribution of homoeolog specialization to the favorable yield phenotype remains to be resolved.Viewed in this way, the study does more than identify a susceptibility factor. It offers a potential route toward precision breeding in which resistance is combined with preserved or improved yield. This favorable combination makes TaNSUN2 relevant beyond the immediate wheat-CWMV system. Nevertheless, broader applicability will require direct testing across additional viruses, wheat backgrounds, and environmental conditions.Within a pathobiome-aware framework, host regulators that alter both pathogen fitness and host physiology can be considered candidate nodes of disease compatibility, although such network-level effects have not been demonstrated for TaNSUN2. This framing is relevant in wheat because the three TaNSUN2 homoeologs are not equivalent: TaNSUN2-5A is preferentially associated with the viral response, whereas TaNSUN2-5B appears more closely linked to root development. TaNSUN2 may therefore be viewed as a dosage-sensitive regulatory node at the intersection of epitranscriptomic control, polyploid genome organization, and disease compatibility. Targeting one homoeolog could potentially shift viral compatibility while other copies maintain the broader developmental program. This remains a hypothesis-generating interpretation and should not be taken as evidence that TaNSUN2 remodels rhizosphere or phyllosphere communities.Parallel evidence from tropical polyploid and clonally propagated crops supports the broader breeding logic. Cultivated banana germplasm arose through hybridization and polyploidization and is characterized by high heterozygosity, clonal propagation, and reduced fertility, all of which complicate conventional resistance breeding [19].Nevertheless, susceptibility-focused genome editing has proved effective: editing the banana DMR6 orthologue enhanced resistance to bacterial disease [20], and targeted knockout of MusaENODL3 increased resistance to Xanthomonas wilt [21]. These studies do not identify TaNSUN2-like epitranscriptomic regulators, but they show that host-encoded vulnerability nodes can be reconfigured in genetically complex crops.The comparison therefore concerns a shared breeding logic, not a shared TaNSUN2 pathway.A related pattern is emerging in sugarcane, another highly polyploid crop in which conventional breeding is constrained by genome complexity and redundancy [22].Recent studies identify actionable host-side targets, including the negative regulators ScWRKY2 and ScCAX4 [23; 24], and virus-exploited host factors such as ScHSP17.5 and ScHSP17.9A, which facilitate sugarcane mosaic virus replication [25]. Together, these findings suggest that crop improvement in complex genomes may benefit from identifying and weakening recurrent host dependencies. In this context, TaNSUN2 should be viewed as a candidate host-dependency node whose possible pathobiomelevel relevance remains a testable hypothesis.