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1. Maize resistance to insect herbivory is enhanced by silencing expression of genes for jasmonate-isoleucine degradation using sugarcane mosaic virus

   Chung S, S. Z (June 2022, Plant direct)

   Previously, sugarcane mosaic virus (SCMV) was developed as a vector for transient expression of heterologous genes in Zea mays (maize). Here, we show that SCMV can also be applied for virus-induced gene silencing (VIGS) of endogenous maize genes. Comparison of sense and antisense VIGS constructs targeting maize phytoene desaturase (PDS) showed that antisense constructs resulted in a greater reduction in gene expression. In a time course of gene expression after infection with VIGS constructs targeting PDS, lesion mimic 22 (Les22), and Iodent japonica 1 (Ij1), efficient expression silencing was observed 2, 3, and 4 weeks after infection with SCMV. However, at Week 5, expression of Les22 and Ij1 was no longer significantly reduced compared with control plants. The defense signaling molecule jasmonate-isoleucine (JA-Ile) can be inactivated by 12C-hydroxylation and hydrolysis, and knockout of these genes leads to herbivore resistance. JA-Ile hydroxylases and hydrolases have been investigated in Arabidopsis, rice, and Nicotiana attenuata. To determine whether the maize homologs of these genes function in plant defense, we silenced expression of ZmCYP94B1 (predicted JA-Ile hydroxylase) and ZmJIH1 (predicted JA-Ile hydrolase) by VIGS with SCMV, which resulted in elevated expression of two defense-related genes, Maize Proteinase Inhibitor (MPI) and Ribosome Inactivating Protein 2 (RIP2). Although ZmCYP94B1 and ZmJIH1 gene expression silencing increased resistance to Spodoptera frugiperda (fall armyworm), Schistocerca americana (American birdwing grasshopper), and Rhopalosiphum maidis (corn leaf aphid), there was no additive effect from silencing the expression of both genes. Further work will be required to determine the more precise functions of these enzymes in regulating maize defenses. 

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2. Maize resistance to insect herbivory is enhanced by silencing expression of genes for jasmonate-isoleucine degradation using sugarcane mosaic virus

   Chung S, S. Z (June 2022, Plant direct)

   Previously, sugarcane mosaic virus (SCMV) was developed as a vector for transient expression of heterologous genes in Zea mays (maize). Here, we show that SCMV can also be applied for virus-induced gene silencing (VIGS) of endogenous maize genes. Comparison of sense and antisense VIGS constructs targeting maize phytoene desaturase (PDS) showed that antisense constructs resulted in a greater reduction in gene expression. In a time course of gene expression after infection with VIGS constructs targeting PDS, lesion mimic 22 (Les22), and Iodent japonica 1 (Ij1), efficient expression silencing was observed 2, 3, and 4 weeks after infection with SCMV. However, at Week 5, expression of Les22 and Ij1 was no longer significantly reduced compared with control plants. The defense signaling molecule jasmonate-isoleucine (JA-Ile) can be inactivated by 12C-hydroxylation and hydrolysis, and knockout of these genes leads to herbivore resistance. JA-Ile hydroxylases and hydrolases have been investigated in Arabidopsis, rice, and Nicotiana attenuata. To determine whether the maize homologs of these genes function in plant defense, we silenced expression of ZmCYP94B1 (predicted JA-Ile hydroxylase) and ZmJIH1 (predicted JA-Ile hydrolase) by VIGS with SCMV, which resulted in elevated expression of two defense-related genes, Maize Proteinase Inhibitor (MPI) and Ribosome Inactivating Protein 2 (RIP2). Although ZmCYP94B1 and ZmJIH1 gene expression silencing increased resistance to Spodoptera frugiperda (fall armyworm), Schistocerca americana (American birdwing grasshopper), and Rhopalosiphum maidis (corn leaf aphid), there was no additive effect from silencing the expression of both genes. Further work will be required to determine the more precise functions of these enzymes in regulating maize defenses. 

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3. Maize resistance to insect herbivory is enhanced by silencing expression of genes for jasmonate‐isoleucine degradation using sugarcane mosaic virus

   https://doi.org/10.1002/pld3.407  

   Chung, Seung Ho; Zhang, Shudi; Song, Hojun; Whitham, Steven A.; Jander, Georg (June 2022, Plant Direct)

   Abstract Previously, sugarcane mosaic virus (SCMV) was developed as a vector for transient expression of heterologous genes inZea mays(maize). Here, we show that SCMV can also be applied for virus‐induced gene silencing (VIGS) of endogenous maize genes. Comparison of sense and antisense VIGS constructs targeting maizephytoene desaturase(PDS) showed that antisense constructs resulted in a greater reduction in gene expression. In a time course of gene expression after infection with VIGS constructs targetingPDS,lesion mimic 22(Les22), andIodent japonica 1(Ij1), efficient expression silencing was observed 2, 3, and 4 weeks after infection with SCMV. However, at Week 5, expression ofLes22andIj1was no longer significantly reduced compared with control plants. The defense signaling molecule jasmonate‐isoleucine (JA‐Ile) can be inactivated by 12C‐hydroxylation and hydrolysis, and knockout of these genes leads to herbivore resistance. JA‐Ile hydroxylases and hydrolases have been investigated in Arabidopsis, rice, andNicotiana attenuata. To determine whether the maize homologs of these genes function in plant defense, we silenced expression ofZmCYP94B1(predicted JA‐Ile hydroxylase) andZmJIH1(predicted JA‐Ile hydrolase) by VIGS with SCMV, which resulted in elevated expression of two defense‐related genes,Maize Proteinase Inhibitor(MPI) andRibosome Inactivating Protein 2(RIP2). AlthoughZmCYP94B1andZmJIH1gene expression silencing increased resistance toSpodoptera frugiperda(fall armyworm),Schistocerca americana(American birdwing grasshopper), andRhopalosiphum maidis(corn leaf aphid), there was no additive effect from silencing the expression of both genes. Further work will be required to determine the more precise functions of these enzymes in regulating maize defenses. 

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4. An unexpected role for tomato threonine deaminase 2 in host defense against bacterial infection

   https://doi.org/10.1093/plphys/kiac584  

   Yeo, In-Cheol; de Azevedo Manhaes, Ana Marcia; Liu, Jun; Avila, Julian; He, Ping; Devarenne, Timothy P (December 2022, Plant Physiology)

   Abstract The hormones salicylic acid (SA) and jasmonic acid (JA) often act antagonistically in controlling plant defense pathways in response to hemibiotrophs/biotrophs (hemi/biotroph) and herbivores/necrotrophs, respectively. Threonine deaminase (TD) converts threonine to α-ketobutyrate and ammonia as the committed step in isoleucine (Ile) biosynthesis and contributes to JA responses by producing the Ile needed to make the bioactive JA–Ile conjugate. Tomato (Solanum lycopersicum) plants have two TD genes: TD1 and TD2. A defensive role for TD2 against herbivores has been characterized in relation to JA–Ile production. However, it remains unknown whether TD2 is also involved in host defense against bacterial hemi/biotrophic and necrotrophic pathogens. Here, we show that in response to the bacterial pathogen-associated molecular pattern (PAMP) flagellin flg22 peptide, an activator of SA-based defense responses, TD2 activity is compromised, possibly through carboxy-terminal cleavage. TD2 knockdown (KD) plants showed increased resistance to the hemibiotrophic bacterial pathogen Pseudomonas syringae but were more susceptible to the necrotrophic fungal pathogen Botrytis cinerea, suggesting TD2 plays opposite roles in response to hemibiotrophic and necrotrophic pathogens. This TD2 KD plant differential response to different pathogens is consistent with SA- and JA-regulated defense gene expression. flg22-treated TD2 KD plants showed high expression levels of SA-responsive genes, whereas TD2 KD plants treated with the fungal PAMP chitin showed low expression levels of JA-responsive genes. This study indicates TD2 acts negatively in defense against hemibiotrophs and positively against necrotrophs and provides insight into a new TD2 function in the elaborate crosstalk between SA and JA signaling induced by pathogen infection. 

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5. Enabling the study of gene function in gymnosperms: Virus‐induced gene silencing in Ephedra tweedieana

   https://doi.org/10.1002/aps3.70027  

   Garcia, Anthony_G K; Bùi, Jo Trang; Michael, Todd P; Ickert‐Bond, Stefanie M; Di_Stilio, Verónica S (December 2025, Applications in Plant Sciences)

   Abstract PremiseAs the sister clade to angiosperms, extant gymnosperms are crucial for reconstructing ancestral gene regulatory networks in seed plants. This highlights the need for model systems representing each of their distinct lineages. However, tools to quickly and effectively investigate gene function in gymnosperms are still limited due to the challenges of long life cycles and large genome sizes. Species within the xerophytic genusEphedra(Gnetales) have comparatively smaller genomes and shrubby growth habits with shorter life spans, making them better suited for greenhouse cultivation and laboratory experiments. MethodsWe implement virus‐induced gene silencing (VIGS) to manipulate gene expression inEphedra tweedieanaviaAgrobacterium‐mediated vacuum infiltration of tobacco rattle virus (TRV1 and TRV2) into seedlings. ResultsTreatment resulted in highly efficient gene silencing of theE. tweedieana PHYTOENE DESATURASE(PDS) orthologEtwPDS. The expected photobleaching phenotype was observed as early as two weeks, and lasted at least five months in stems, shoot tips, leaves, axillary meristems, and lateral branches of treated plants. DiscussionWe report on virus‐induced targeted gene silencing ofPDSin a Gnetales representative to further enable functional studies of the genetic mechanisms underpinning adaptations in gymnosperms, an important and underrepresented lineage of seed plants. 

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