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NONEXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1) is the master regulator of salicylic acid-mediated basal and systemic acquired resistance in plants. Here, we report that NPR1 plays a pivotal role in restricting compatible infection by turnip mosaic virus, a member of the largest plant RNA virus genus Potyvirus, and that such resistance is counteracted by NUCLEAR INCLUSION B (NIb), the viral RNA-dependent RNA polymerase. We demonstrate that NIb binds to the SUMO-interacting motif 3 (SIM3) of NPR1 to prevent SUMO3 interaction and sumoylation, while sumoylation of NIb by SUMO3 is not essential but can intensify the NIb–NPR1 interaction. We discover that the interaction also impedes the phosphorylation of NPR1 at Ser11/Ser15. Moreover, we show that targeting NPR1 SIM3 is a conserved ability of NIb from diverse potyviruses. These data reveal a molecular "arms race" by which potyviruses deploy NIb to suppress NPR1-mediated resistance through disrupting NPR1 sumoylation. Salicylic acid (SA) signaling pathway restricts the compatible infection of potyviruses. Here, Liu et al. show that potyviral NIb interacts with NPR1, the SA receptor in plants, preventing its sumoylation by SUMO3 and subsequent phosphorylation at Ser11/Ser15. This way, NPR1-mediated immunity is suppressed to promote virus infection. [ABSTRACT FROM AUTHOR]

Cytosine residues in mammalian DNA occur in five forms: cytosine (C), 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). The ten-eleven translocation (Tet) dioxygenases convert 5mC to 5hmC, 5fC and 5caC in three consecutive, Fe(n)-and α-ketoglutarate-dependent oxidation reactions (1-4). The Tet family of dioxygenases is widely distributed across the tree of life (5), including in the heterolobosean amoeboflagellate Naegleria gruberi. The genome of Naegleria (6) encodes homologues of mammalian DNA methyltransferase and Tet proteins (7). Here we study biochemically and structurally one of the Naegleria Tet-like proteins (NgTetl), which shares significant sequence conservation (approximately 14% identity or 39% similarity) with mammalian Tetl. Like mammalian Tet proteins, NgTetl acts on 5mC and generates 5hmC, 5fC and 5caC. The crystal structure of NgTetl in complex with DNA containing a 5mCpG site revealed that NgTetl uses a base-flipping mechanism to access 5mC. The DNA is contacted from the minor groove and bent towards the major groove. The flipped 5mC is positioned in the active-site pocket with planar stacking contacts, Watson-Crick polar hydrogen bonds and van der Waals interactions specific for 5mC. The sequence conservation between NgTetl and mammalian Tetl, including residues involved in structural integrity and functional significance, suggests structural conservation across phyla., The free-living amoeboflagellate Naegleria gruberi has eight Tet/ JBP-like dioxygenases (NgTet1-8; Extended Data Fig. 1). The NgTet proteins vary in length, but all contain a conserved core region of ~210 [...]

Summary: AVRPPHB SUSCEPTIBLE 3 (PBS3) belongs to the GH3 family of acyl acid amido synthetases, which conjugates amino acids to diverse acyl acid substrates. Recent studies demonstrate that PBS3 in Arabidopsis plays a key role in the biosynthesis of plant defense hormone salicylic acid (SA) by catalyzing the conjugation of glutamate to isochorismate to form isochorismate‐9‐glutamate, which is then used to produce SA through spontaneous decay or ENHANCED PSEUDOMONAS SUSCEPTIBILITY (EPS1) catalysis. Consistent with its function as an essential enzyme for SA biosynthesis, PBS3 is well known to be a positive regulator of plant immunity in Arabidopsis. Additionally, PBS3 is also involved in the trade‐off between abiotic and biotic stress responses in Arabidopsis by suppressing the inhibitory effect of abscisic acid on SA‐mediated plant immunity. Besides stress responses, PBS3 also plays a role in plant development. Under long‐day conditions, PBS3 influences Arabidopsis flowering time by regulating the expression of flowering regulators FLOWERING LOCUS C and FLOWERING LOCUS T. Taken together, PBS3 functions in the signaling network of plant development and responses to biotic and/or abiotic stresses, but the molecular mechanisms underlying its diverse roles remain obscure. [ABSTRACT FROM AUTHOR]