RNA interference of NtNCED3 reduces drought tolerance and impairs plant growth through feedback regulation of isoprenoids in Nicotiana tabacum

Abscisic acid (ABA) regulates plant growth and development and responses to various abiotic stresses. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) catalyses the crucial rate-limiting step in ABA biosynthesis. Here, we isolated two variants of the NCED3 gene (NtNCED3-1 and NtNCED3-2) from tobacco. Our study suggested that NtNCED3 is mainly expressed in the roots, stems, and young upper leaves, and is rapidly induced by drought and heavy metal stress. The promoter of NtNCED3-2 contains a number of abiotic stress-responsive cis-acting elements. RNA interference-based silencing of NtNCED3-2 reduced the ABA content and drought tolerance of tobacco. Suppression of NtNCED3-2 also inhibited primary root development and root hair growth, led to a stunted phenotype, and reduced the number of leaf glandular trichomes. Compared with wild type plant, NtNCED3-2 knockdown plants had reduced diterpenoids, photosynthetic pigments, plant hormone contents, and lower expression of related genes in the isoprenoid metabolism pathway, which resulted in lower photosynthetic ability. Taken together, our results indicate that NtNCED3-2 is involved in the response to drought stress and the regulation of plant growth and development via feedback regulation of the isoprenoid metabolism pathway flux.