Isochorismate‐based salicylic acid biosynthesis confers basal resistance to Fusarium graminearum in barley

Abstract

Salicylic acid (SA) plays an important role in signal transduction and disease resistance. In Arabidopsis, SA can be made by either of two biosynthetic branches, one involving isochorismate synthase (ICS) and the other involving phenylalanine ammonia-lyase (PAL). However, the biosynthetic pathway and the importance of SA remain largely unknown in Triticeae. Here, we cloned one ICS and seven PAL genes from barley, and studied their functions by their overexpression and suppression in that plant. Suppression of the ICS gene significantly delayed plant growth, whereas PAL genes, both overexpressed and suppressed, had no significant effect on plant growth. Similarly, suppression of ICS compromised plant resistance to Fusarium graminearum, whereas similar suppression of PAL genes had no significant effect. We then focused on transgenic plants with ICS. In a leaf-based test with F. graminearum, transgenic plants with an up-regulated ICS were comparable with wild-type control plants. By contrast, transgenic plants with a suppressed ICS lost the ability to accumulate SA during pathogen infection and were also more susceptible to Fusarium than the wild-type controls. This suggests that ICS plays a unique role in SA biosynthesis in barley, which, in turn, confers a basal resistance to F. graminearum by modulating the accumulation of H O , O2- and reactive oxygen-associated enzymatic activities. Although SA mediates systemic acquired resistance (SAR) in dicots, there was no comparable SAR response to F. graminearum in barley. This study expands our knowledge about SA biosynthesis in barley and proves that SA confers basal resistance to fungal pathogens.

Maize phenylalanine ammonia‐lyases contribute to resistance to Sugarcane mosaic virus infection, most likely through positive regulation of salicylic acid accumulation

“…VIGS‐mediated inhibition of ZmPAL genes expression shows that in maize the increased expression of these ZmPAL genes and the consequent increase in activity of the phenylpropanoid pathway is required for SA biosynthesis and activation of SA‐dependent defensive signalling. Thus, maize differs from Arabidopsis or barley, in which the isochorismate pathway is the predominant biosynthetic route for SA production (Hao et al ., ; Wildermuth et al ., ), or soybean, in which the phenylpropanoid and isochorismate pathways are equally important (Shine et al ., ). It appears that the phenylpropanoid pathway is the major route for biosynthesis of SA in maize.…”

“…However, the biosynthetic pathway for SA has been determined in only a few plant species. In Arabidopsis thaliana and barley ( Hordeum vulgare ), most SA biosynthesis is dependent on isochorismate synthase (ICS) activity (Hao et al ., ; Wildermuth et al ., ). In tobacco ( Nicotiana tabacum ) SA is predominantly synthesized from benzoic acid derived from the phenylpropanoid pathway (phenylalanine) (Lee et al ., ), in peach ( Prunus persica ) SA is also produced from benzoic acid derived from phenylalanine via an alternative pathway (Diaz‐Vivancos et al ., ), whilst in soybean ( Glycine max ) the isochorismate and phenylpropanoid pathways are equally important in supplying the carbon skeletons for SA biosynthesis (Shine et al ., ).…”

Salicylic Acid Biosynthesis in Plants

“…The first pathway for SA biosynthesis starts from chorismate, which is converted into isochorismate (IC) by ICS ( Figure 1; Catinot et al, 2008;Abreu and Munne-Bosch, 2009;Hao et al, 2018). This pathway was first discovered in bacteria.…”

“…Since then, the importance of SA in plant defense to biotic and abiotic stimuli has been well established. SA levels are known to increase in many pathosystems upon infection with viruses, fungi, insects, and bacteria (Ogawa et al, 2006;Kim and Hwang, 2014;Hao et al, 2018;Zhao et al, 2019), and exogenous SA treatment boosts the defense system of the host (Nahar et al, 2011;Wang and Liu, 2012;Tripathi et al, 2019;Zhang and Li, 2019). Plants overexpressing NahG, a salicylate hydroxylase degrading SA, are unable to accumulate SA upon pathogen infection and are impaired in their systemic acquired resistance (SAR), a broad-spectrum systemic resistance acquired after a primary infection (Lawton et al, 1995).…”

Deterioration of Antioxidant Competence in Barley Lesion Mimic Mutant 194

“…This method normalizes the expression of a specific gene versus a control reference with the formula 2 −△△CT . Actin was evaluated as the control genes [27]. Information on the genes analyzed is listed in Tab.…”