Summary: Sugarcane mosaic virus (SCMV) is a pathogen of worldwide importance that causes dwarf mosaic disease on maize ( Zea mays ). Until now, few maize genes/proteins have been shown to be involved in resistance to SCMV. In this study, we characterized the role of maize phenylalanine ammonia‐lyases (ZmPALs) in accumulation of the defence signal salicylic acid (SA) and in resistance to virus infection. SCMV infection significantly increased SA accumulation and expression of SA‐responsive pathogenesis‐related protein genes ( PR s). Interestingly, exogenous SA treatment decreased SCMV accumulation and enhanced resistance. Both reverse transcription‐coupled quantitative PCR and RNA‐Seq data confirmed that expression levels of at least four ZmPAL genes were significantly up‐regulated upon SCMV infection. Knockdown of ZmPAL expression led to enhanced SCMV infection symptom severity and virus multiplication, and simultaneously resulted in decreased SA accumulation and PR gene expression. Intriguingly, application of exogenous SA to SCMV‐infected ZmPAL ‐silenced maize plants decreased SCMV accumulation, showing that ZmPALs are required for SA‐mediated resistance to SCMV infection. In addition, lignin measurements and metabolomic analysis showed that ZmPALs are also involved in SCMV‐induced lignin accumulation and synthesis of other secondary metabolites via the phenylpropanoid pathway. In summary, our results indicate that ZmPALs are required for SA accumulation in maize and are involved in resistance to virus infection by limiting virus accumulation and moderating symptom severity.

Tobacco (Nicotiana benthamiana) and Turnip mosaic virus (TuMV) were used as a model system to investigate the potential of engineered nanomaterials (ENMs) for promoting crop growth and resistance to viral infection. A 5 mL ENM suspension of 50 or 200 mg L⁻¹ consisting of either two metal-based nanoparticles (NP Fe₂O₃ or TiO₂) or two carbon-based nanomaterials (NMs) (MWCNTs or C₆₀) was foliar-sprayed onto the leaf surface of tobacco daily for 21 days. Fully developed young leaves were then inoculated with TuMV tagged with GFP and were cultivated for 5 days. Exposure to both metal- and carbon-based NMs significantly increased the shoot biomass by approximately 50%. TEM images demonstrated that exposure to NMs did not alter cellular integrity; both NP Fe₂O₃ and TiO₂ preferentially accumulated in chloroplasts. Fluorescence images of TuMV abundance on the leaf surfaces suggest that NMs significantly inhibited viral proliferation as measured by the fluorescence intensity on the newly emerged leaves. Approximately 15–60% decreases in the relative amount of TuMV coat proteins could further explain the mechanisms by which NMs suppressed viral infection. Increases in phytohormone levels of 40% also suggest that NMs play an important role in stimulating plant growth and activating defense mechanisms. These findings contribute to our understanding of the sustainable use of ENMs in agriculture.

Plant viruses, as obligate intracellular parasites, induce significant changes in the cellular physiology of host cells to facilitate their multiplication. These alterations often lead to the development of symptoms that interfere with normal growth and development, causing USD 60 billion worth of losses per year, worldwide, in both agricultural and horticultural crops. However, existing literature often lacks a clear and concise presentation of the key information regarding the mechanisms underlying plant virus-induced symptoms. To address this, we conducted a comprehensive review to highlight the crucial interactions between plant viruses and host factors, discussing key genes that increase viral virulence and their roles in influencing cellular processes such as dysfunction of chloroplast proteins, hormone manipulation, reactive oxidative species accumulation, and cell cycle control, which are critical for symptom development. Moreover, we explore the alterations in host metabolism and gene expression that are associated with virus-induced symptoms. In addition, the influence of environmental factors on virus-induced symptom development is discussed. By integrating these various aspects, this review provides valuable insights into the complex mechanisms underlying virus-induced symptoms in plants, and emphasizes the urgency of addressing viral diseases to ensure sustainable agriculture and food production.