Metabolic engineering of beta-carotene in orange fruit increases its in vivo antioxidant properties

Orange is a major crop and an important source of health-promoting bioactive compounds. Increasing the levels of specific antioxidants in orange fruit through metabolic engineering could strengthen the fruit's health benefits. In this work, we have afforded enhancing the -carotene content of orange fruit through blocking by RNA interference the expression of an endogenous -carotene hydroxylase gene (Cs-CHX) that is involved in the conversion of -carotene into xanthophylls. Additionally, we have simultaneously overexpressed a key regulator gene of flowering transition, the FLOWERING LOCUS T from sweet orange (CsFT), in the transgenic juvenile plants, which allowed us to obtain fruit in an extremely short period of time. Silencing the Cs-CHX gene resulted in oranges with a deep yellow (golden') phenotype and significant increases (up to 36-fold) in -carotene content in the pulp. The capacity of -carotene-enriched oranges for protection against oxidative stress in vivo was assessed using Caenorhabditis elegans as experimental animal model. Golden oranges induced a 20% higher antioxidant effect than the isogenic control. This is the first example of the successful metabolic engineering of the -carotene content (or the content of any other phytonutrient) in oranges and demonstrates the potential of genetic engineering for the nutritional enhancement of fruit tree crops

Resistance of True Citrus species to Diaphorina citri

Host genetic resistance is a promising strategy for the management of Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and consequently Huanglongbing (HLB). To date, no study has investigated the resistance to D. citri in the clonal and vegetatively propagated plants of the Microcitrus, Eremocitrus, and Atalantia genera. This study assesses Near and True Citrus genotype antixenosis and antibiosis against D. citri, with trichome density and volatile emission as possible mechanisms of resistance.Peer reviewe

Acta Horticulturae

Volatile organic compounds, most of them being terpenes, are signals emitted by plants for communication with the environment. Orange fruit accumulates mainly terpenes in mature peel oil glands with D-limonene accounting for approximately 97% of terpene content. We have generated transgenic orange plants carrying a D-limonene synthase gene in antisense (AS) configuration. Transgenic expression caused a dramatic decrease in the accumulation of D-limonene in fruit peels, being about 80-100 times lower in AS samples than in empty vector (EV) transgenic ones. This affected the interaction of fruits with their biotic environment because they resulted in resistance to different specialized pathogens. When antisense fruits were challenged with the fungus Penicillium digitatum, they showed marked resistance against this pathogen. A gene expression analysis of these fruits linked the decrease of D-limonene to upregulation of genes involved in the innate immunity response. High D-limonene content in mature orange peels may be a signal for attractiveness of microorganisms which might be likely involved in facilitating the access to the pulp of seed dispersal frugivores

TERPENE DOWN-REGULATION TRIGGERS INNATE IMMUNITY AND RESISTANCE TO FUNGAL PATHOGENS IN ORANGE FRUITS

Volatile organic compounds, most of them being terpenes, are signals emitted by plants for communication with the environment. Orange fruit accumulates mainly terpenes in mature peel oil glands with D-limonene accounting for approximately 97% of terpene content. We have generated transgenic orange plants carrying a D-limonene synthase gene in antisense (AS) configuration. Transgenic expression caused a dramatic decrease in the accumulation of D-limonene in fruit peels, being about 80-100 times lower in AS samples than in empty vector (EV) transgenic ones. This affected the interaction of fruits with their biotic environment because they resulted in resistance to different specialized pathogens. When antisense fruits were challenged with the fungus Penicillium digitatum, they showed marked resistance against this pathogen. A gene expression analysis of these fruits linked the decrease of D-limonene to upregulation of genes involved in the innate immunity response. High D-limonene content in mature orange peels may be a signal for attractiveness of microorganisms which might be likely involved in facilitating the access to the pulp of seed dispersal frugivores