Tangerine tomato roots show increased accumulation of acyclic carotenoids, less abscisic acid, drought sensitivity, and impaired endomycorrhizal colonization.

The Heirloom Golden tangerine tomato fruit variety is highly nutritious due to accumulation of tetra-cis-lycopene, that has a higher bioavailability and recognised health benefits in treating anti-inflammatory diseases compared to all-trans-lycopene isomers found in red tomatoes. We investigated if photoisomerization of tetra-cis-lycopene occurs in roots of the MicroTom tangerine (tang) tomato and how this affects root to shoot biomass, mycorrhizal colonization, abscisic acid accumulation, and responses to drought. tang plants grown in soil under glasshouse conditions displayed a reduction in height, number of flowers, fruit yield, and root length compared to wild-type (WT). Soil inoculation with Rhizophagus irregularis revealed fewer arbuscules and other fungal structures in the endodermal cells of roots in tang relative to WT. The roots of tang hyperaccumulated acyclic cis-carotenes, while only trace levels of xanthophylls and abscisic acid were detected. In response to a water deficit, leaves from the tang plants displayed a rapid decline in maximum quantum yield of photosystem II compared to WT, indicating a defective root to shoot signalling response to drought. The lack of xanthophylls biosynthesis in tang roots reduced abscisic acid levels, thereby likely impairing endomycorrhizal colonisation and drought-induced root to shoot signalling.