The Strawberry Fruit Fra a Allergen Functions in Flavonoid Biosynthesis

Abstract

The strawberry Fra a 1 allergen is a homolog of the major birch pollen allergen Bet v 1. It is synthesized by red ripe fruits of Fragaria x ananassa while white fruits of a mutant genotype, which is known to be tolerated by individuals affected by allergy, are devoid of it. Proteomic analyses have shown that Fra a 1 is down-regulated in the tolerated white-fruited genotype along with enzymes of the anthocyanin pigment pathway. In this study, we report the spatial and temporal expression of three Fra a genes that encode different isoforms, and the transient RNAi-mediated silencing of the Fra a genes in strawberry fruits of the red-fruited cultivar Elsanta with an ihpRNA construct. As a consequence of reduced levels of Fra a mRNAs, fruits were obtained that produced significantly decreased levels of anthocyanins and upstream metabolites. This effect is consistent with the parallel down-regulation of the phenylalanine ammonia lyase (FaPAL) and to a lesser extent of the chalcone synthase (FaCHS) transcript levels also found in these fruits. In naturally occurring white-fruited genotypes of F. chiloensis and F. vesca, Fra a transcript levels are higher than those of the red-fruited varieties, likely to compensate for the low expression levels of FaPAL and FaCHS in these mutant genotypes. The results demonstrate that Fra a expression is directly linked to flavonoid biosynthesis and show that the Fra a allergen has an essential biological function in pigment formation in strawberry fruit.

Transcription Factor-Mediated Control of Anthocyanin Biosynthesis in Vegetative Tissues

“…Another GO category, antioxidant activity, comprised five peroxidases, four of which were strongly down-regulated upon ROS1/DEL expression in roots. In the GO category, response to biotic stimuli, we found three highly up-regulated genes (from 87-fold to 160-fold), which encode homologs of the birch pollen allergen Bet v 1 (Muñoz et al, 2010), whereas other genes from the same protein family were down-regulated by ROS1/DEL.…”

“…The Bet v 1 protein family encodes small lipocalin-like proteins with a hydrophobic core, which may contain polyphenolic compounds such as quercetin (Roth-Walter et al, 2014). A function of these proteins in anthocyanin accumulation was previously suggested from work in strawberry, where downregulation of Fra a1, a BetV1 homolog, led to colorless fruits (Muñoz et al, 2010).…”

Acylphloroglucinol biosynthesis in strawberry fruit

“…In addition, complex feedback mechanisms controlling anthocyanin synthesis have been described (Muñoz et al, 2010). Although the four candidate genes studied are probably not directly involved in flavonoid formation, their function may be required for the coordinate progression of the ripening process, and they may have different roles for the different classes of phenolics (Fig.…”

Las proteínas PR10 de plantas: estructura sin función

“…En el centro de ambos hechos está una proteína de la familia PR10 denominada Fra. El silenciamiento específico de Fra en los frutos de fresa ha permitido establecer que esta proteína puede ser un elemento regulador en la producción de flavonoides (4). Estudios cristalográficos y biofísicos han identificado a algunos flavonoides, como la catequina o la naringenina, como ligandos específicos de las proteínas Fra (5) …”