Heat Stress Pre-Exposure May Differentially Modulate Plant Defense to Powdery Mildew in a Resistant and Susceptible Barley Genotype

Abstract

Heat stress negatively affects barley production and under elevated temperatures defense responses to powdery mildew (Blumeria graminis f. sp. hordei, Bgh) are altered. Previous research has analyzed the effects of short-term (30 s to 2 h) heat stress, however, few data are available on the influence of long-term exposure to heat on powdery mildew infections. We simultaneously assessed the effects of short and long term heat pre-exposure on resistance/susceptibility of barley to Bgh, evaluating powdery mildew infection by analyzing symptoms and Bgh biomass with RT-qPCR in barley plants pre-exposed to high temperatures (28 and 35 °C from 30 s to 5 days). Plant defense gene expression after heat stress pre-exposure and inoculation was also monitored. Our results show that prolonged heat stress (24, 48 and 120 h) further enhanced Bgh susceptibility in a susceptible barley line (MvHV118-17), while a resistant line (MvHV07-17) retained its pathogen resistance. Furthermore, prolonged heat stress significantly repressed the expression of several defense-related genes (BAX inhibitor-1, Pathogenesis related-1b and Respiratory burst oxidase homologue F2) in both resistant and susceptible barley lines. Remarkably, heat-suppressed defense gene expression returned to normal levels only in MvHV07-17, a possible reason why this barley line retains Bgh resistance even at high temperatures.

Near-Isogenic Barley Lines Show Enhanced Susceptibility to Powdery Mildew Infection Following High-Temperature Stress

“…Importantly, in our assays, we used intact barley plants as opposed to the experiments of Schwarzbach [ 26 ], where leaf segments were placed on agar medium, a likely cause of differential reactions of heat-stressed barley (35–36 °C for 1 and 2 h) to Bgh in the susceptible line. Recently, we found that prolonged heat stress pre-exposure (35 °C for 24, 48, and 120 h) confers enhanced susceptibility to Bgh in a susceptible barley line, while a resistant line retains its pathogen resistance [ 28 ]. Defense gene expression patterns following heat stress and Bgh inoculation were markedly different in the resistant and susceptible lines.…”

“…To analyze Bgh biomass, a protocol of reverse transcription followed by quantitative real-time polymerase chain reaction (RT-qPCR) was used as described previously for barley-Bgh and wheat- Puccinia striiformis f. sp. tritici interactions [ 28 , 69 ]. Collected leaf tissue was ground in liquid nitrogen.…”

“…However, in this case, the absence of powdery mildew symptoms is likely due to the inhibition of pathogen growth at constant high temperatures rather than the activation of plant defense responses. We found that prolonged heat stress pre-exposure (24, 48, and 120 h at 35 °C) confers enhanced susceptibility to Bgh in a genetically susceptible barley line (MvHV 118-17), while a resistant line (MvHV 07-17) retains its pathogen resistance [ 28 ]. A robust reactivation of heat-suppressed defense gene expression in the barley line MvHV07-17 is a likely reason for retaining Bgh resistance even after a prolonged pre-exposure to 35 °C [ 28 ].…”

“…Recently, we found that prolonged heat stress pre-exposure confers enhanced susceptibility to Bgh in a genetically susceptible barley line, while pathogen resistance is retained in a resistant line [ 28 ]. Therefore, we hypothesized that prolonged heat stress may similarly increase the Bgh susceptibility of wild-type Ingrid ( Mlo genotype), a genetically well-characterized barley cultivar.…”

Selection of Candidate Genes Conferring Blast Resistance and Heat Tolerance in Rice through Integration of Meta-QTLs and RNA-Seq

“…However, rice frequently suffers from various biotic and abiotic stresses in nature [ 3 , 4 ]. As a consequence of global warming, the combination of pathogens and high temperatures (HT) frequently exists in the cultivation of cereal crops [ 5 , 6 , 7 , 8 ]. As the “cancer” of rice, M. oryzae is widely distributed, and terribly destructive under favorable conditions, which can cause severe yield losses in rice [ 9 , 10 , 11 ].…”