Activated malate circulation contributes to the manifestation of light-dependent mosaic symptoms

The role of reactive oxygen species in plant-virus interactions

Reactive oxygen species (ROS) play a complex role in interactions between plant viruses and their host plants. They can both help the plant defend against viral infection and support viral infection and spread. This review explores the various roles of ROS in plant-virus interactions, focusing on their involvement in symptom development and the activation of plant defense mechanisms. The article discusses how ROS can directly inhibit viral infection, as well as how they can regulate antiviral mechanisms through various pathways involving miRNAs, virus-derived small interfering RNAs, viral proteins, and host proteins. Additionally, it examines how ROS can enhance plant resistance by interacting with hormonal pathways and external substances. The review also considers how ROS might promote viral infection and transmission, emphasizing their intricate role in plant-virus dynamics. These insights offer valuable guidance for future research, such as exploring the manipulation of ROS-related gene expression through genetic engineering, developing biopesticides, and adjusting environmental conditions to improve plant resistance to viruses. This framework can advance research in plant disease resistance, agricultural practices, and disease control.

The C4 photosynthesis bifunctional enzymes, PDRPs, of maize are co-opted to cytoplasmic viral replication complexes to promote infection of a prevalent potyvirus sugarcane mosaic virus

In maize, two pyruvate orthophosphate dikinase (PPDK) regulatory proteins, ZmPDRP1 and ZmPDRP2, are respectively specific to the chloroplast of mesophyll cells (MCs) and bundle sheath cells (BSCs). Functionally, ZmPDRP1/2 catalyse both phosphorylation/inactivation and dephosphorylation/activation of ZmPPDK, which is implicated as a major rate-limiting enzyme in C4 photosynthesis of maize. Our study here showed that maize plants lacking ZmPDRP1 or silencing of ZmPDRP1/2 confer resistance to a prevalent potyvirus sugarcane mosaic virus (SCMV). We verified that the C-terminal domain (CTD) of ZmPDRP1 plays a key role in promoting viral infection while independent of enzyme activity. Intriguingly, ZmPDRP1 and ZmPDRP2 re-localize to cytoplasmic viral replication complexes (VRCs) following SCMV infection. We identified that SCMV-encoded cytoplasmic inclusions protein CI targets directly ZmPDRP1 or ZmPDRP2 or their CTDs, leading to their re-localization to cytoplasmic VRCs. Moreover, we found that CI could be degraded by the 26S proteasome system, while ZmPDRP1 and ZmPDRP2 could up-regulate the accumulation level of CI through their CTDs by a yet unknown mechanism. Most importantly, with genetic, cell biological and biochemical approaches, we provide evidence that BSCs-specific ZmPDRP2 could accumulate in MCs of Zmpdrp1 knockout (KO) lines, revealing a unique regulatory mechanism crossing different cell types to maintain balanced ZmPPDK phosphorylation, thereby to keep maize normal growth. Together, our findings uncover the genetic link of the two cell-specific maize PDRPs, both of which are co-opted to VRCs to promote viral protein accumulation for robust virus infection.

Transcriptional Regulation of SugarCane Response to Sporisorium scitamineum: Insights from Time-Course Gene Coexpression and Ca2+ Signaling

Sugarcane response to Sporisorium scitamineum is determined by multiple major genes and numerous microeffector genes. Here, time-ordered gene coexpression networks were applied to explore the interaction between sugarcane and S. scitamineum. Totally, 2459 differentially expressed genes were identified and divided into 10 levels, and several stress-related subnetworks were established. Interestingly, the Ca2+ signaling pathway was activated to establish the response to sugarcane smut disease. Accordingly, two CAX genes (ScCAX2 and ScCAX3) were cloned and characterized from sugarcane. They were significantly upregulated under ABA stress but inhibited by MeJA treatment. Furthermore, overexpression of ScCAX2 and ScCAX3 enhanced the susceptibility of transgenic plants to the pathogen infection, suggesting its negative role in disease resistance. A regulatory model for ScCAX genes in disease response was thus depicted. This work helps to clarify the transcriptional regulation of sugarcane response to S. scitamineum stress and the function of the CAX gene in disease response.

Maize catalases are recruited by a virus to modulate viral multiplication and infection

Given the detrimental effects of excessive reactive oxygen species (ROS) accumulation in plant cells, various antioxidant mechanisms have evolved to maintain cellular redox homeostasis, encompassing both enzymatic components (e.g., catalase, superoxide dismutase) and non-enzymatic ones. Despite extensive research on the role of antioxidant systems in plant physiology and responses to abiotic stresses, the potential exploitation of antioxidant enzymes by plant viruses to facilitate viral infection remains insufficiently addressed. Herein, we demonstrate that maize catalases (ZmCATs) exhibited up-regulated enzymatic activities upon sugarcane mosaic virus (SCMV) infection. ZmCATs played crucial roles in SCMV multiplication and infection by catalysing the decomposition of excess cellular H2 O2 and promoting the accumulation of viral replication-related cylindrical inclusion (CI) protein through interaction. Peroxisome-localized ZmCATs were found to be distributed around SCMV replication vesicles in Nicotiana benthamiana leaves. Additionally, the helper component-protease (HC-Pro) of SCMV interacted with ZmCATs and enhanced catalase activities to promote viral accumulation. This study unveils a significant involvement of maize catalases in modulating SCMV multiplication and infection through interaction with two viral factors, thereby enhancing our understanding regarding viral strategies for manipulating host antioxidant mechanisms towards robust viral accumulation.

Sugarcane mosaic virus employs 6K2 protein to impair ScPIP2;4 transport of H2O2 to facilitate virus infection

Sugarcane mosaic virus (SCMV), one of the main pathogens causing sugarcane mosaic disease, is widespread in sugarcane (Saccharum spp. hybrid) planting areas and causes heavy yield losses. RESPIRATORY BURST OXIDASE HOMOLOG (RBOH) NADPH oxidases and plasma membrane intrinsic proteins (PIPs) have been associated with the response to SCMV infection. However, the underlying mechanism is barely known. In the present study, we demonstrated that SCMV infection upregulates the expression of ScRBOHs and the accumulation of hydrogen peroxide (H2O2), which inhibits SCMV replication. All eight sugarcane PIPs (ScPIPs) interacted with SCMV-encoded protein 6K2, whereby two PIP2s (ScPIP2;1 and ScPIP2;4) were verified as capable of H2O2 transport. Furthermore, we revealed that SCMV-6K2 interacts with ScPIP2;4 via transmembrane domain 5 to interfere with the oligomerization of ScPIP2;4, subsequently impairing ScPIP2;4 transport of H2O2. This study highlights a mechanism adopted by SCMV to employ 6K2 to counteract the host resistance mediated by H2O2 to facilitate virus infection and provides potential molecular targets for engineering sugarcane resistance against SCMV.

Unraveling the Mechanisms of Virus-Induced Symptom Development in Plants

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.