| Summary: | Carotenoids function as photosynthetic accessory pigments, antioxidants, and vitamin A precursors. We recently showed that transgenic sweetpotato calli overexpressing the mutant sweetpotato (<i>Ipomoea batatas</i> [L.] Lam) <i>Orange</i> gene (<i>IbOr</i>-<i>R96H</i>), which carries a single nucleotide polymorphism responsible for Arg to His substitution at amino acid position 96, exhibited dramatically higher carotenoid content and abiotic stress tolerance than calli overexpressing the wild-type <i>IbOr</i> gene (<i>IbOr</i>-<i>WT</i>). In this study, we generated transgenic sweetpotato plants overexpressing <i>IbOr</i>-<i>R96H</i> under the control of the cauliflower mosaic virus (CaMV) <i>35S</i> promoter via <i>Agrobacterium</i>-mediated transformation. The total carotenoid contents of <i>IbOr</i>-<i>R96H</i> storage roots (light-orange flesh) and <i>IbOr</i>-<i>WT</i> storage roots (light-yellow flesh) were 5.4–19.6 and 3.2-fold higher, respectively, than those of non-transgenic (NT) storage roots (white flesh). The β-carotene content of <i>IbOr</i>-<i>R96H</i> storage roots was up to 186.2-fold higher than that of NT storage roots. In addition, <i>IbOr</i>-<i>R96H</i> plants showed greater tolerance to heat stress (47 °C) than NT and <i>IbOr</i>-<i>WT</i> plants, possibly because of higher DPPH radical scavenging activity and ABA contents. These results indicate that <i>IbOr</i>-<i>R96H</i> is a promising strategy for developing new sweetpotato cultivars with improved carotenoid contents and heat stress tolerance.
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