![]() It comprises nearly 300 genes of Carbohydrate-Active enZymes (CAZymes) and selectively attacks the cell wall polysaccharide substrates depending on the carbohydrate composition of the invaded plant tissue ( Blanco-Ulate et al., 2014). The fungus has a predominantly necrotrophic lifestyle that involves killing plant host cells by diverse phytotoxic compounds and degrading enzymes, after which it extracts nutrients from the dead cells. cinerea causes disease in more than 200 plant species including numerous economically important crops such as tomatoes and grapes ( AbuQamar et al., 2016). These two pathways are mostly antagonistic and the balance of crosstalk between them affects the outcome of the pathology ( Glazebrook, 2005). The classic dogma is that jasmonic acid (JA) and ethylene signaling activates resistance against necrotrophs while the salicylic acid (SA) signaling pathway is important to fight biotrophic pathogens, although it also plays some role in the defense against the necrotrophic fungi Botrytis cinerea ( Ferrari et al., 2003, Govrin & Levine, 2000, Vuorinen et al., 2021). The identity of the pathogen determines the type of systemic response. Plants activate local defenses against invading pathogens within minutes and within hours, levels of resistance in distal tissue influenced by systemic signals mediated by plant hormones. Other defense responses require the detection of the invading pathogen by the plant and the activation of inducible responses, often culminating in deliberate localized cell suicide in the form of the hypersensitive response (HR) in order to limit pathogen spread ( Gilchrist, 1998, Heath, 2000b). These preformed compounds are either stored in their biologically active forms like saponins ( Podolak et al., 2010), or as precursors that are converted to toxic antimicrobial molecules only after pathogen attack, exemplified by the glucosinolate - myrosinase system ( Wittstock & Halkier, 2002). If the first line of defense is breached, then the plant must resort to a different set of chemical mechanisms in the form of toxic secondary metabolites and antimicrobial peptides, which are ready to be released upon cell damage ( Tam et al., 2015). Constitutive defenses include preformed physical barriers composed of cell walls, waxy epidermal cuticle, bark and resins ( Heath, 2000a). Plants are resistant to most pathogens in spite of their sessile nature because they evolved a wide variety of constitutive and inducible defense mechanisms. Plants must continuously adapt and protect themselves both against abiotic stressors (drought, extreme temperatures, improper lighting and excessive salinity) as well as biotic stress imposed by other organisms such as viruses, bacteria, fungi and insects. thaliana and is integrated into several important pathways such as plant microbe perception and hormone signaling. As a whole, our results suggest that IQD1 is an important defensive protein against Botrytis cinerea in A. cinerea and in regulating GS accumulation and it is dependent on JAR1 controlling indole glucosinolate accumulation. Epistasis relations between IQD1 OXP and mutants defective in plant-hormone signaling indicated that IQD1 acts upstream or parallel to the hormonal pathways (JA/ET and SA) in defense response against B. Moreover, quantification of SA, JA and abscisic acids in IQD1 OXP and iqd1-1lines compared to WT showed a significant reduction in endogenous JA levels in the knockout line simultaneously with increased SA levels. Further examination revealed a marked reduction of SA/JA signaling and increase in ethylene signaling genes in the iqd1-1 line. Comparison of whole transcriptome expression between iqd1-1 and wild type revealed a substantial downregulation of genes involved in plant defense and hormone regulation. Furthermore, we show that IQD1 is upregulated by Jasmonic acid (JA) and downregulated by Salicylic acid (SA). We demonstrate here that the IQD1 overexpressing line ( IQD1 OXP) is more resistant also to the necrotrophic fungus Botrytis cinerea, whereas an IQD1 knockout line ( iqd1-1) is much more sensitive. thaliana, which was found to be a positive regulator of glucosinolate (GS) accumulation and plant defense responses against insects. IQ Domain 1 (IQD1) is a novel calmodulin-binding protein in A.
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