The Comparison of Temporal Transcriptome Changes Between Morning-Opening and Afternoon-Opening Iris Flowers Reveals the Candidate Genes Regulating Flower Opening and Closing

The circadian clock allows plants to synchronize their flower opening and closing rhythms with daily environmental changes to enhance fertility and adaptability. Flowers of Iris dichotoma, I. domestica and their hybrids are ephemeral and present robust opening and closing rhythms. To reveal the key genes regulating flower opening and closing, transcriptome changes during the same time course but different flowering processes were compared between two F-2 hybrid plants of Iris dichotoma and I. domestica with divergent flower opening and closing times. Clock-related gene PHYTOCHROME-INTERACTING FACTOR 4-like was specifically down-regulated during flower starting opening and was specifically up-regulated during flower starting closing. Genes promoting auxin synthesis, auxin efflux, auxin signaling, cellular water uptake, cell wall loosening and the increase of osmotic pressure were specifically up-regulated during flower starting opening, suggesting their positive regulation on the start of a flower opening. The overexpression of auxin-responsive gene SMALL AUXIN UP-REGULATED RNA 64-like in tobacco promoted flower opening of tobacco. During flower starting closing, genes promoting cell wall synthesis and loosening, cellular water uptake and osmoregulation were specifically down-regulated, while genes promoting the degradation of cell wall and protein were specifically up-regulated. The results improve the understanding of regulatory networks of flower opening and closing.

Automated summary

The circadian clock regulates the opening and closing rhythms of flowers. Clock-related genes show specific expression changes during the flower opening and closing processes. Genes promoting auxin synthesis, signaling, and cellular water uptake are up-regulated during flower opening, while genes promoting cell wall loosening and osmotic pressure increase are also up-regulated. On the other hand, genes promoting cell wall and protein degradation are up-regulated during flower closing, while genes promoting cell wall synthesis and regeneration are down-regulated.