Overexpression of phytoglobin in barley alters both compatible and incompatible interactions with the mildew pathogen Blumeria graminis

Abstract

This study showed how barley plants can be shifted in their response to isolates of the mildew pathogen Blumeria graminis with different host adaptation by overexpression of the barley phytoglobin gene HvHb1. At early infection stages, plants overexpressing phytoglobin (GPHb1) showed less papilla formation and more hypersensitive response against both virulent and avirulent pathogen isolates compared to the wildtype (WT) plants. The shift was most pronounced in a wheat‐adapted isolate (B. graminis f. sp. tritici). At later infection stages, GPHb1 plants infected with a virulent pathogen isolate (A6) showed less leaf chlorosis compared to the WT plants, indicating delayed senescence. The chlorophyll level was significantly higher in A6‐infected GPHb1 plants 9 days after inoculation (dai) and the senescence indicators sphingosine‐1‐phosphate:ceramide ratio and phytol content confirmed delayed senescence. At 14 dai the percentage of fungal DNA was significantly higher on the GPHb1 plants than on WT plants, probably as a result of the delayed senescence. The results show that overexpression of phytoglobin (previously known as plant haemoglobin) can be an important tool to understand disease‐related stress effects in plants of agronomic importance and for understanding basic resistance mechanisms. Studying this process in more detail may provide insights into how to alleviate stress‐related senescence in plants.

The effect of phytoglobin overexpression on the plant proteome during nonhost response of barley (Hordeum vulgare) to wheat powdery mildew (Blumeria graminis f. sp. tritici)

“…This is consistent with the observation that during a pathogen attack, the plant activates a network of pathways to resist the pathogen invasion, which usually requires thousands of protein 10 . WT plants were characterized by twice as many DAP proteins than the plants with overexpression of phytoglobin (Table 1), that confirms what was found by Sørensen et al 8 in other words that overexpression of Hb suppresses the response to pathogens. In the following sections we will describe DAP belonging to specific functional categories and sub-categories particularly relevant to the inoculation process, the innate immunity of the two genotypes and the signal transduction pathways.…”

“…Therefore, plants characterized by a reduced amount of MLO should have an increased frequency of PCD. The results obtained by Sørensen et al 8 indicate that this is the case in plants with overexpression of phytoglobins during nonhost response.…”

“…In the following sections we will describe DAP belonging to specific functional categories and sub-categories particularly relevant to the inoculation process, the innate immunity of the two genotypes and the signal transduction pathways. Time point selected for analysis was 72 hai as the progression of inoculation is different between two genotypes as determined by Sørensen et al 8 . Barley plants with overexpression of hemoglobin were characterized by less papillae formation and higher rate of hypersensitive reaction both with and without haustorium formation after 72 hai.…”

“…Barley plants with overexpression of hemoglobin were characterized by less papillae formation and higher rate of hypersensitive reaction both with and without haustorium formation after 72 hai. This data published by Sørensen et al 8 is summarized in Supplementary Table S4.…”

“…of B. graminis such as B. graminis f. sp. tritici adapted to wheat (Triticum aestivum L.) 8 or B. graminis f. sp. avenae, the powdery mildew of oat (Avena sativa L.).…”