Immunity elicitors for induced resistance against the downy mildew pathogen in pearl millet

Senapathyhally Nagaraju Lavanya,Sujesh Sudarsan,Siddaiah Chandra Nayaka,Rakesh Srivastava,H Rajashekara,Sathyanarayana Niranjan-Raj,C Tarasatyavati,Ragi Jadimurthy,Vijai Kumar Gupta

doi:10.1038/s41598-022-07839-4

Abstract

Pearl millet (Pennisetum glaucum (L.) R. Br.) is a globally important cereal whose production is severely constrained by downy mildew caused by Sclerospora graminicola (Sacc.). In this study, immunity eliciting properties of 3,5-dichloroanthranilic acid (DCA), Cell Wall Glucan (CWG), Lipopolysaccharide (LPS), and Glycinebetaine (GB) was deciphered through enzymatic and protein studies based on elicitor treatment activated defense mechanisms. Glycinebetaine, LPS, CWS and DCA elicited enzyme activities and gene expression of the defense enzymes, such as β-1,3-glucanase, phenylalanine ammonia lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO), lipoxygenase (LOX) and defense protein hydroxyproline-rich glycoproteins (HRGPs). However, the speed and the extent of elicitation differed. High levels of enzyme activities and gene expression in elicitor-treated P. glaucum positively correlated with the increased downy mildew resistance. A very rapid and large changes in elicitor-treated seedlings, in contrast to the delayed, smaller changes in the untreated susceptible control seedlings suggests that the rate and magnitude of defense gene expression are important for effective manifestation of defense against pathogen. As compared to other elicitors and control, GB promoted increase in enzyme activities and gene expression, implicating that GB is a promising elicitor of downy mildew resistance in P. glaucum.

Highlights

Phenylalanine ammonia lyase activity was gradually increased after 3 h of incubation and its peak was obtained after 6 h in the elicitor treated samples and resistant seedlings
In pathogen-inoculated seedlings, phenylalanine ammonia lyase (PAL) activity peaked at 6 hpi in resistant and elicitor treated seedlings, while in susceptible control seedlings PAL activity peaked at 9 hpi
Chitinase, PAL, POX, polyphenol oxidase (PPO), LOX, catalase, and hydroxyproline-rich glycoproteins (HRGPs) all play a vital role, and the speed and intensity with which these defensive enzymes and proteins are triggered and accumulated is strongly connected with the degree of resistance elicited by that particular elicitor

Summary

Introduction

Glycinebetaine, LPS, CWS and DCA elicited enzyme activities and gene expression of the defense enzymes, such as β-1,3-glucanase, phenylalanine ammonia lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO), lipoxygenase (LOX) and defense protein hydroxyproline-rich glycoproteins (HRGPs). High levels of enzyme activities and gene expression in elicitor-treated P. glaucum positively correlated with the increased downy mildew resistance. Treatment with β- Aminobutyric Acid (BABA) stimulated defense responses in squash plants, and resulted in resistance to powdery mildew fungus, which correlated with the increased expression of PR-1, PAL and POX24 genes. Spray treatment of pea plants with different elicitors such as SA, P. fluorescens, Chitosan, and T. harzianum induced higher levels of phenols, POX, PAL, and PPO leading to resistance against the rust pathogen Uromyces viciae–fabae (Pers.) J.

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