Deregulation of ζ-carotene desaturase in Arabidopsis and tomato exposes a unique carotenoid-derived redundant regulation of floral meristem identity and function.

A level of redundancy and interplay among the transcriptional regulators of floral development safeguards the plant's reproductive success, and ensures crop production. Herein, an additional layer of complexity in the regulation of floral meristem (FM) identity and flower development is elucidated linking carotenoid biosynthesis and metabolism to the regulation of determinate flowering. The accumulation and subsequent cleavage of a diverse array of ζ-carotenes in the chloroplast biogenesis 5 (clb5) mutant of Arabidopsis results in the reprogramming of meristematic gene regulatory networks establishing FM identity mirroring that of the FM identity master regulator, APETALA1 (AP1). The immediate transition to floral development in clb5 requires long photoperiods in a GIGANTEA-independent manner, while AP1 is essential for clb5's floral organ development. The elucidation of this link between carotenoid metabolism and floral development translates to tomato exposing a novel regulation of FM identity redundant to and initiated by AP1 and proposed to be dependent on the E class floral initiation and organ identity regulator, SEPALLATA3 (SEP3).