Abstract
Specific syntaxins, such as Arabidopsis AtPEN1 and its barley ortholog ROR2, play a major role in plant defense against powdery mildews. Indeed, the impairment of these genes results in increased fungal penetration in both host and non-host interactions. In this study, a genome-wide survey allowed the identification of 21 tomato syntaxins. Two of them, named SlPEN1a and SlPEN1b, are closely related to AtPEN1. RNAi-based silencing of SlPEN1a in a tomato line carrying a loss-of-function mutation of the susceptibility gene SlMLO1 led to compromised resistance toward the tomato powdery mildew fungus Oidium neolycopersici. Moreover, it resulted in a significant increase in the penetration rate of the non-adapted powdery mildew fungus Blumeria graminis f. sp. hordei. Codon-based evolutionary analysis and multiple alignments allowed the detection of amino acid residues that are under purifying selection and are specifically conserved in syntaxins involved in plant-powdery mildew interactions. Our findings provide both insights on the evolution of syntaxins and information about their function which is of interest for future studies on plant–pathogen interactions and tomato breeding.
Highlights
In eukaryotic cells, compartmentalization through the endomembrane apparatus and exocytosis require a highly regulated transport system
Twenty-one putative syntaxins were retrieved in the tomato genome with a BLAST search using the Arabidopsis AtPEN1 amino acid sequence as input
The distribution of Arabidopsis syntaxins within the clades fully matched with their previous assignment to the five subfamilies SYP-1, -2, -3, -4, -8 (Sanderfoot et al, 2000)
Summary
Compartmentalization through the endomembrane apparatus and exocytosis require a highly regulated transport system. Soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) proteins are involved in such a transport, as they mediate the fusion of membranes of cargo-containing small shuttles, referred to as vesicles, and target membranes (Lipka et al, 2007). According to their localization, SNARE proteins can be classified into vesicle-associated (v-SNAREs) and target-membrane-associated (t-SNAREs) (Söllner et al, 1993). SNARE proteins can be classified into vesicle-associated (v-SNAREs) and target-membrane-associated (t-SNAREs) (Söllner et al, 1993) They can be classified into Q-SNARE and R-SNARE proteins, which contain either arginine or glutamine at the center of the SNARE domain, respectively (Fasshauer et al, 1998). Syntaxins of the Qa SNARE family can be divided into five subfamilies known as SYP-1, -2, -3, -4, -8 (Sanderfoot et al, 2000; Bock et al, 2001)
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