Myeong‐Je Cho

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mutants display enhanced resistance against different classes of pathogens, such as bacteria, oomycete, and fungi. Notably, disease resistance correlates with increased salicylic acid (SA) levels and transcriptional activation of immune responses. Furthermore, we demonstrate that SlDMR6-1 and SlDMR6-2 display SA-5 hydroxylase activity, thus contributing to the elucidation of the enzymatic function of DMR6. We then propose that SlDMR6 duplication in tomato resulted in subsequent subfunctionalization, in which SlDMR6-2 specialized in balancing SA levels in flowers/fruits, while SlDMR6-1 conserved the ability to fine-tune SA levels during pathogen infection of the plant vegetative tissues. Overall, this work not only corroborates a mechanism underlying SA homeostasis in plants, but also presents a promising strategy for engineering broad-spectrum and durable disease resistance in crops.

Significance Plants employ nucleotide-binding leucine-rich repeat (NLR) immune receptors to recognize pathogen effectors and to activate effector-triggered immunity (ETI). The Toll/IL-1 receptor-NLR (TNL) protein (Roq1) recognizes the effectors XopQ and HopQ1 in an Enhanced Disease Susceptibility 1 (EDS1)-dependent way in Nicotiana benthamiana . Interestingly, we found that the coiled-coil NLR protein N requirement gene 1 (NRG1) is required for activation of ETI by the TNLs Roq1 and Recognition of Peronospora parasitica 1. NRG1 interacts with EDS1 and acts downstream of Roq1 and EDS1 to mediate XopQ/HopQ1-triggered ETI. In addition, Roq1, EDS1, and NRG1 mediate XopQ-triggered transcriptional changes in N. benthamiana and regulate resistance to Xanthomonas and Pseudomonas species that carry the effectors XopQ or HopQ1. This study suggests that NRG1 may be a conserved key component in TNL-mediated signaling pathways.

Thioredoxins are 12-kDa proteins functional in the regulation of cellular processes throughout the animal, plant, and microbial kingdoms. Growing evidence with seeds suggests that an h-type of thioredoxin, reduced by NADPH via NADP-thioredoxin reductase, reduces disulfide bonds of target proteins and thereby acts as a wakeup call in germination. A better understanding of the role of thioredoxin in seeds as well as other systems could be achieved if more were known about the target proteins. To this end, we have devised a strategy for the comprehensive identification of proteins targeted by thioredoxin. Tissue extracts incubated with reduced thioredoxin are treated with a fluorescent probe (monobromobimane) to label sulfhydryl groups. The newly labeled proteins are isolated by conventional two-dimensional electrophoresis: (i) nonreducing/reducing or (ii) isoelectric focusing/reducing SDS/PAGE. The isolated proteins are identified by amino acid sequencing. Each electrophoresis system offers an advantage: the first method reveals the specificity of thioredoxin in the reduction of intramolecular vs. intermolecular disulfide bonds, whereas the second method improves the separation of the labeled proteins. By application of both methods to peanut seed extracts, we isolated at least 20 thioredoxin targets and identified 5-three allergens (Ara h2, Ara h3, and Ara h6) and two proteins not known to occur in peanut (desiccation-related and seed maturation protein). These findings open the door to the identification of proteins targeted by thioredoxin in a wide range of systems, thereby enhancing our understanding of its function and extending its technological and medical applications.