Carotenoid fortification of zucchini fruits using a viral RNA vector

BACKGROUND

Carotenoids are health-promoting metabolites in livestock and human diets. Some important crops have been genetically modified to increase their content. Although the usefulness of transgenic plants to alleviate nutritional deficiencies is obvious, their social acceptance has been controversial.

RESULTS

Here, we demonstrate an alternative biotechnological strategy for carotenoid fortification of edible fruits in which no transgenic DNA is involved. A viral RNA vector derived from Zucchini yellow mosaic virus (ZYMV) was modified to express a bacterial phytoene synthase (crtB), and inoculated to zucchini (Cucurbita pepo L.) leaves nurturing pollinated flowers. After the viral vector moved to the developing fruit and expressed crtB, the rind and flesh of the fruits developed yellow-orange rather than green color. Metabolite analyses showed a substantial enrichment in health-promoting carotenoids, such as α- and β-carotene (provitamin A), lutein and phytoene, in both rind and flesh.

CONCLUSION

Although this strategy is perhaps not free from controversy due to the use of genetically modified viral RNA, our work does demonstrate the possibility of metabolically fortifying edible fruits using an approach in which no transgenes are involved. This article is protected by copyright. All rights reserved.

Exploiting Partial Resistance to Tomato yellow leaf curl virus Derived from Solanum pimpinellifolium UPV16991

Tomato yellow leaf curl disease (TYLCD) causes great economic losses in tomato crops worldwide. Despite efforts undertaken by different research groups, there are no immune commercial plant materials available. Recently, our group reported partial resistance to TYLCD in line L102, derived from Solanum pimpinellifolium UPV16991. Resistance in this line is monogenic, with partial recessiveness and incomplete penetrance. Even though the resistance gene in L102 is not dominant, we also proved that levels of resistance were high in hybrids with different tomato lines. The objective of this work was to evaluate the level of resistance in plants which combined UPV16991-derived resistance and the Ty-1 gene, both in heterozygosis. Most of the hybrids between S. pimpinellifolium- and S. chilense-derived resistant lines exhibited milder symptoms than heterozygotes for either S. pimpinellifolium- or S. chilense-derived resistance. In some of the hybrids, viral accumulation was also lower than in respective heterozygotes. Our results support the utility of resistance derived from UPV16991 combined with the Ty-1 gene in increasing levels of resistance to TYLCD in tomato hybrids. This is the most practical approach to exploiting resistance derived from UPV16991, because it allows the development of hybrids without the need of fixing the resistance gene in both parents.

Inheritance of Tomato yellow leaf curl virus Resistance Derived from Solanum pimpinellifolium UPV16991

Resistance to tomato yellow leaf curl disease (TYLCD) in accession UPV16991 Solanum pimpinellifolium has been previously reported by our group. A breeding program was developed from an initial S. lycopersicum × S. pimpinellifolium UPV16991 cross. This first cross was followed by several selfing generations. Selection for resistance to Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) was carried out for plants of each generation. One partially resistant F₆ plant (L102) was chosen to form the family to study the genetic control of resistance to TYLCV. Crosses between four breeding lines susceptible to TYLCD and L102 were also performed to study the dominance of the resistance in S. lycopersicum genetic backgrounds. Response to TYLCV infection of P₁, P₂, F₁, F₂, BC₁, and BC₂ generations fitted, for this line, a monogenic control with partial recessiveness and incomplete penetrance. The percentage of homozygotic plants with partial resistance was 72.75. Among the four hybrids developed, the highest levels of resistance were found in the hybrid formed from the most vigorous S. lycopersicum line. These results must be considered for breeding purposes. Partial resistance derived from UPV16991 will be useful in homozygosis or combined with resistance genes from other sources.