Novel Plant Immune-Priming Compounds Identified via High-Throughput Chemical Screening Target Salicylic Acid Glucosyltransferases in Arabidopsis    

Abstract

Plant activators are compounds, such as analogs of the defense hormone salicylic acid (SA), that protect plants from pathogens by activating the plant immune system. Although some plant activators have been widely used in agriculture, the molecular mechanisms of immune induction are largely unknown. Using a newly established high-throughput screening procedure that screens for compounds that specifically potentiate pathogen-activated cell death in Arabidopsis thaliana cultured suspension cells, we identified five compounds that prime the immune response. These compounds enhanced disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous SA, but reduced its metabolite, SA-O-β-d-glucoside. Inducing compounds inhibited two SA glucosyltransferases (SAGTs) in vitro. Double knockout plants that lack both SAGTs consistently exhibited enhanced disease resistance. Our results demonstrate that manipulation of the active free SA pool via SA-inactivating enzymes can be a useful strategy for fortifying plant disease resistance and may identify useful crop protectants.

Nicotinate O-Glucosylation Is an Evolutionarily Metabolic Trait Important for Seed Germination under Stress Conditions in Arabidopsis thaliana

“…This observation is consistent with the theory that catalytic promiscuity serves as the starting point for the acquisition of new enzymatic functions: The evolutionally new enzyme here adopted one of the minor activities of its ancestor (Aharoni et al, 2005;Weng et al, 2012). The important role of UGT74F1 in the plant innate immune system was recently demonstrated (Noutoshi et al, 2012). This result, together with the important role of UGT74F2 in seed germination proved in this study, provides an explanation for the maintenance of the UGT74F1/UGT74F2 pairs in the genomes of current Brassicaceae plants.…”

“…UGT74F1 showed similar activity to BA, o-ABA, and SA (only SAG was produced) (Supplemental Figure 2). Moreover, we did not detect NAOGT activity with the recently identified SAGT (AT3G11340, UGT76B1) from Arabidopsis, although the SAGT activity of UGT76B1 was confirmed (Noutoshi et al, 2012;Supplemental Figure 3). …”

“…This phenomenon is similar to what is known of SA glucosides in Arabidopsis: SGEs can be detected transiently at the early stages of pathogen infection. SAG is then induced to higher levels upon pathogen infection (Dempsey et al, 2011;Noutoshi et al, 2012). In the case of NA modifications in Arabidopsis, the content of NANG can increase up to around 200-fold higher than that of the wild type, suggesting that NANG is a stable end product in Arabidopsis.…”

Pipecolic Acid Orchestrates Plant Systemic Acquired Resistance and Defense Priming via Salicylic Acid-Dependent and -Independent Pathways

“…Furthermore, exogenous SA or pretreatment with chemicals such as 2,6-dichloroisonicotinic acid or S-methyl-1,2,3-benzothiadiazole-7-carbothioate (BTH), which are often vaguely designated as SA analogs, are able to prime cultured plant cells or intact plants for enhanced defense responses (Kauss et al, 1992;Thulke and Conrath, 1998), and BTHinduced priming proceeds via the SA downstream regulator NPR1 (Kohler et al, 2002). Moreover, treatments with chemicals that inhibit SA glycosylation and thereby endogenously elevate free SA levels lead to priming responses in Arabidopsis (Noutoshi et al, 2012), and defense priming triggered by exogenous b-amino butyric acid or the bacterial quorum sensing compound N-acylhomoserine lactone requires an intact SA signaling pathway (Zimmerli et al, 2000;Schenk et al, 2014). Our study reveals a differentiated role of SA in the defense priming responses associated with SAR: SA is required to prime plants for enhanced activation of certain defense responses but is dispensable for the potentiation of others.…”

Plant Chemical Genetics: From Phenotype-Based Screens to Synthetic Biology

“…and other fungal species, namely oxytriazine, triclosan, fluazinam, cantharidin, enpiclonil, two trichothecene-type mycotoxins, 4,15-diacetoxyscirpenol, and neosolaniol (Serrano et al, 2007(Serrano et al, , 2010. A high-throughput screen for compounds that facilitate pathogen-activated cell death in cultured suspension cells of Arabidopsis revealed the imprimatins that prime immune responses and enhance disease resistance against Pseudomonas syringae in Arabidopsis through the possible inhibition of salicylic acid glucosyltransferases (Noutoshi et al, 2012b).…”