Significance: Phosphate (Pi) deficiency constrains plant development and productivity in both natural and agricultural ecosystems. An interaction among Pi and Fe availability controls the developmental program that allows the Arabidopsis root system to more effectively explore the topsoil where Pi accumulates. Analysis of mutants unable to establish root architecture responses to low Pi allowed the identification of mutant alleles of STOP1 (a transcription factor) and ALMT1 (a malate transporter), two genes previously reported to play a role in the malate-mediated tolerance to toxic levels of aluminum. We show that these genes underlie a malate-exudation–dependent mechanism of Fe relocation in the root apical meristem that is essential for reprogramming root growth under low-Pi conditions.

Summary: Infection caused by the synergistic interaction of two plant viruses is typically manifested by severe symptoms and increased accumulation of either virus. In potex–potyviral synergism, the potyviral RNA silencing suppressor helper component proteinase (HCPro) is known to enhance the pathogenicity of the potexvirus counterpart. In line with this, Potato virus X (PVX; genus Potexvirus ) genomic RNA (gRNA) accumulation and gene expression from subgenomic RNA (sgRNA) are increased in Nicotiana benthamiana by Potato virus A (PVA; genus Potyvirus ) HCPro expression. Recently, we have demonstrated that PVA HCPro interferes with the host cell methionine cycle by interacting with its key enzymes S ‐adenosyl‐ l ‐methionine synthetase (SAMS) and S ‐adenosyl‐ l ‐homocysteine hydrolase (SAHH). To study the involvement of methionine cycle enzymes in PVX infection, we knocked down SAMS and SAHH. Increased PVX sgRNA expression between 3 and 9 days post‐infiltration (dpi) and upregulation of (–)‐strand gRNA accumulation at 9 dpi were observed in the SAHH‐silenced background. We found that SAMS and SAHH silencing also caused a significant reduction in glutathione (GSH) concentration, specifically in PVX‐infected plants between 2 and 9 dpi. Interestingly, HCPro expression in PVX‐infected plants caused an even stronger reduction in GSH levels than did SAMS + SAHH silencing and a similar level of reduction was also achieved by knocking down GSH synthetase. PVX sgRNA expression was increased in the GSH synthetase‐silenced background. GSH is a major antioxidant of plant cells and therefore GSH shortage may explain the strong oxidative stress and severe symptoms observed during potex–potyvirus mixed infection.

Advances in next-generation sequencing have facilitated the discovery of a multitude of long non-coding RNAs (lncRNAs) with pleiotropic functions in cellular processes, disease, and viral pathogenesis. It came as no surprise when viruses were also revealed to transcribe their own lncRNAs. Among them, gammaherpesviruses, one of the three subfamilies of the Herpesviridae, code their largest number. These structurally and functionally intricate non-coding (nc) transcripts modulate cellular and viral gene expression to maintain viral latency or prompt lytic reactivation. These lncRNAs allow for the virus to escape cytosolic surveillance, sequester, and re-localize essential cellular factors and modulate the cell cycle and proliferation. Some viral lncRNAs act as “messenger molecules”, transferring information about viral infection to neighboring cells. This broad range of lncRNA functions is achieved through lncRNA structure-mediated interactions with effector molecules of viral and host origin, including other RNAs, proteins and DNAs. In this review, we discuss examples of gammaherpesvirus-encoded lncRNAs, emphasize their unique structural attributes, and link them to viral life cycle, pathogenesis, and disease progression. We will address their potential as novel targets for drug discovery and propose future directions to explore lncRNA structure and function relationship.

Papaya ringspot virus (PRSV), a common potyvirus infecting papaya plants worldwide, can lead to either antagonism or synergism in mixed infections with Papaya mosaic virus (PapMV), a potexvirus. These two unrelated viruses produce antagonism or synergism depending on their order of infection in the plant. When PRSV is inoculated first or at the same time as PapMV, the viral interaction is synergistic. However, an antagonistic response is observed when PapMV is inoculated before PRSV. In the antagonistic condition, PRSV is deterred from the plant and its drastic effects are overcome. Here, we examine differences in gene expression by high-throughput RNA sequencing, focused on immune system pathways. We present the transcriptomic expression of single and mixed inoculations of PRSV and PapMV leading to synergism and antagonism. Upregulation of dominant and hormone-mediated resistance transcripts suggests that the innate immune system participates in synergism. In antagonism, in addition to innate immunity, upregulation of RNA interference-mediated resistance transcripts suggests that adaptive immunity is involved.