Nectar- and stigma exudate-specific expression of an acidic chitinase could partially protect certain apple cultivars against fire blight disease

Anita Kurilla,Zoltan Kerenyi,Timea Toth,Daniel Silhavy,Tamas Lakatos,Zsuzsanna Darula,Laszlo Dorgai,Geza Dallmann

doi:10.1007/s00425-019-03303-2

Anita Kurilla, Zoltan Kerenyi + Show 6 more

Open Access

https://doi.org/10.1007/s00425-019-03303-2

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Abstract

Main conclusionCertain apple cultivars accumulate to high levels in their nectar and stigma exudate an acidic chitinase III protein that can protect against pathogens including fire blight disease causing Erwinia amylovora.To prevent microbial infections, flower nectars and stigma exudates contain various antimicrobial compounds. Erwinia amylovora, the causing bacterium of the devastating fire blight apple disease, is the model pathogen that multiplies in flower secretions and infects through the nectaries. Although Erwinia-resistant apples are not available, certain cultivars are tolerant. It was reported that in flower infection assay, the ‘Freedom’ cultivar was Erwinia tolerant, while the ‘Jonagold’ cultivar was susceptible. We hypothesized that differences in the nectar protein compositions lead to different susceptibility. Indeed, we found that an acidic chitinase III protein (Machi3-1) selectively accumulates to very high levels in the nectar and the stigma exudate of the ‘Freedom’ cultivar. We show that three different Machi3-1 alleles exist in apple cultivars and that only the 5B-Machi3-1 allele expresses the Machi3-1 protein in the nectar and the stigma exudate. We demonstrate that the 5B-Machi3-1 allele was introgressed from the Malus floribunda 821 clone into different apple cultivars including the ‘Freedom’. Our data suggest that MYB-binding site containing repeats of the 5B-Machi3-1 promoter is responsible for the strong nectar- and stigma exudate-specific expression. As we found that in vitro, the Machi3-1 protein impairs growth and biofilm formation of Erwinia at physiological concentration, we propose that the Machi3-1 protein could partially protect 5B-Machi3-1 allele containing cultivars against Erwinia by inhibiting the multiplication and biofilm formation of the pathogen in the stigma exudate and in the nectar.

Highlights

IntroductionSugar-rich fluids such as stigma exudates and nectar to attract pollinators (Tanveer et al 2014)
Plants secrete rewarding, sugar-rich fluids such as stigma exudates and nectar to attract pollinators (Tanveer et al 2014)
Plants were transformed with several deletion constructs generated from the 5B-Machi3-1 plasmid (Fig. 4a, bottom panel), and we studied the accumulation of the Machi3-1 protein in the nectars of the transformants. 15/48 plants expressed Machi3-1 protein in the nectar (Fig. 4a) when the five-box region was present in the promoter

Summary

Introduction

Sugar-rich fluids such as stigma exudates and nectar to attract pollinators (Tanveer et al 2014). Based on their stigma, Angiosperms can be divided into two groups, plants with dry (e.g.: Arabidopsis thaliana) and wet stigma (e.g.: Malus domestica, apple and Nicotiana tabacum, tobacco). While the surface of the dry stigma is covered with a proteinaceous extracuticular layer (pellicle), the wet stigma is covered with stigma exudates (Edlund et al 2004). This fluid secretion plays a critical role in pollen capture, hydration, growth of pollen tube and serves as a reward for the pollinators.

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