Development of chemicals that mimic a carotenoid-derived plant growth regulator zaxinone

Abstract

Zaxinone is a carotenoid-derived bioactive molecule required for normal rice growth and development. Zaxinone functions by enhancing sugar metabolism and regulating SL and cytokinin homeostasis in rice roots. Zaxinone has great agricultural potential due to its growth-promoting activity and its ability to reduce infestation by the root parasitic plant Striga by inhibiting strigolactone (SL) production. However, zaxinone is unstable in the environment and its organic synthesis is laborious. This makes it difficult to use in both basic research and applications. To overcome these inconveniences, easy-to-synthesise and highly effective zaxinone mimics, namely MiZax, have been developed. The conjugated isoprenoid chain of zaxinone has been substituted with aromatic structures, inspired by several successful examples such as the development of fungicides and insecticides from natural isoprenoid bioactive compounds. The β-ionone ring of zaxinone was also replaced by a phenyl ring, which is a common approach in the design of SL analogs. The resulting compounds showed biological activities comparable to those of zaxinone, i.e., they promoted rice growth and mitigated Striga infection by reducing SL levels. In addition, application of these compounds to horticultural crops improved plant growth and performance, as well as fruit yield and quality, demonstrating their usefulness as plant growth regulators. MiZax may have future applications as probes for receptor/binding protein discovery and in chemical genetics to elucidate zaxinone biology.