Engineering fire blight resistance into the apple cultivar ‘Gala’ using the FB_MR5 CC‐NBS‐LRR resistance gene of Malus × robusta 5

Abstract

SummaryThe fire blight susceptible apple cultivar Malus 9 domestica Borkh. cv. 'Gala' was transformed with the candidate fire blight resistance gene FB_MR5 originating from the crab apple accession Malus 9 robusta 5 (Mr5). A total of five different transgenic lines were obtained. All transgenic lines were shown to be stably transformed and originate from different transgenic events. The transgenic lines express the FB_MR5 either driven by the constitutive CaMV 35S promoter and the ocs terminator or by its native promoter and terminator sequences. Phenotyping experiments were performed with Mr5-virulent and Mr5-avirulent strains of Erwinia amylovora, the causal agent of fire blight. Significantly less disease symptoms were detected on transgenic lines after inoculation with two different Mr5-avirulent E. amylovora strains, while significantly more shoot necrosis was observed after inoculation with the Mr5-virulent mutant strain ZYRKD3_1. The results of these experiments demonstrated the ability of a single gene isolated from the native gene pool of apple to protect a susceptible cultivar from fire blight. Furthermore, this gene is confirmed to be the resistance determinant of Mr5 as the transformed lines undergo the same gene-for-gene interaction in the host-pathogen relationship Mr5-E. amylovora.

Molecular response of resistant and susceptible apple genotypes to Erwinia amylovora infection

“…Gala (Malus × domestica Borkh.). All of the five transgenic lines carrying CC-NBS-LRR from Malus×robusta 5 were significantly less susceptible to fire blight than the original cultivar, but the rate of resistance was not high (Broggini et al 2014). Partial resistance to fire blight confers also apple MpNPR1 (Malnoy et al 2007).…”

New biotechnological tools to accelerate scab-resistance trait transfer to apple

“…This suggests that the combination of diverse resistance strategies can improve the field performance of these plants where they are exposed to a wide diversity of pathogens. Besides apple scab, genes conferring resistance to fire blight (Liu et al , 2001; Borejsza-Wysocka et al , 2007; Malnoy et al , 2007; Broggini et al , 2014), Alternaria blotch (Fan et al , 2011), and powdery mildew (James et al , 2004; Caffier and Parisi, 2007; Chen et al , 2012) have been described, and these could be used in conjunction with scab resistant genes in order to obtain multiple resistance via gene pyramiding. Many genes could be readily tested in transient assays with virus-derived vectors instead of generating apple transgenic plants for testing each gene.…”

Identification of SNPs linked to eight apple disease resistance loci

“…For this last purpose, SNP markers seemed most suitable because of their high frequency (between 4.5 and 20 markers/ kbp) in the apple genome (Velasco et al 2010;Micheletti et al 2011) and coupled with the availability of technologies enabling the simultaneous genotyping from a few to thousands of markers per DNA sample. The resistance genes Rvi6, Rvi15, Pl2 and FB_MR5 have been cloned in the last decade (Belfanti et al 2004;Schouten et al 2014;Rikkerink et al 2007;Broggini et al 2014), while for FB_E, positional cloning is in progress (Parravicini et al 2011). Hence, for these last-mentioned genes, the map position is correct and information available on the sequence of the resistance gene itself, markers developed during the positional cloning and/or the sequence of the surrounding genomic regions are available and can be used to facilitate the identification of SNPs closely associated with these genes.…”