Abstract
Plants sense photoperiod signals to confirm the optimal flowering time. Previous studies have shown that Cryptochrome2 (CRY2) functions to promote floral transition in the long-day plant (LDP) Arabidopsis; however, the function and molecular mechanism by which CRY2 regulates floral transition in short-day plants (SDPs) is still unclear. In this study, we identified a CRY2 homologous gene, ClCRY2, from Chrysanthemum lavandulifolium, a typical SDP. The morphological changes in the C. lavandulifolium shoot apex and ClFTs expression analysis under SD conditions showed that adult C. lavandulifolium completed the developmental transition from vegetative growth to reproductive growth after eight SDs. Meanwhile, ClCRY2 mRNA exhibited an increasing trend from 0 to 8 d of SD treatment. ClCRY2 overexpression in wild-type (WT) Arabidopsis and C. lavandulifolium resulted in early flowering. The transcript levels of the CONSTANS-like (COL) genes ClCOL1, ClCOL4, and ClCOL5, and FLOWERING LOCUS T (FT) homologous gene ClFT1 were upregulated in ClCRY2 overexpression (ClCRY2-OE) C. lavandulifolium under SD conditions. The transcript levels of some circadian clock-related genes, including PSEUDO-REPONSE REGULATOR 5 (PRR5), ZEITLUPE (ZTL), FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1), and GIGANTEA (GI-1 and GI-2), were upregulated in ClCRY2-OE C. lavandulifolium, while the expression levels of other circadian clock-related genes, such as EARLY FLOWERING 3 (ELF3), ELF4, LATE ELONGATED HYPOCOTYL (LHY), PRR73, and REVEILLE8 (RVE8), were downregulated in ClCRY2-OE C. lavandulifolium under SD conditions. Taken together, the results suggest that ClCRY2 promotes floral transition by fine-tuning the expression of circadian clock-related gene, ClCOLs and ClFT1 in C. lavandulifolium under SD conditions.
Highlights
Plants sense changes in external circumstances and integrate these signals with internal factors, such as gibberellin and age, to ensure optimal flowering time, which could guarantee the reproduction of the species[1]
Total RNA was extracted from various tissues/organs to examine ClCRY2 expression patterns, and the results showed that ClCRY2 mRNA was highest in the leaves during the C. lavandulifolium floral transition (Fig. 1c)
The results showed that ClCRY2 mRNA abundance was markedly increased with short day (SD) treatment and peaked at 8 d of SD (Fig. 1b)
Summary
Plants sense changes in external circumstances and integrate these signals with internal factors, such as gibberellin and age, to ensure optimal flowering time, which could guarantee the reproduction of the species[1]. CRYs are unique photoreceptors present in all major evolutionary lineages[12] They are flavoproteins with similar sequences to DNA photolyases, which are light-activated DNA repair enzymes that mediate light signals to remove pyrimidine dimers from DNA to repair UV-induced DNA damage[13,14]. CRYs have lost DNA photolyase activity, but possess other biochemical functions[15,16] They regulate floral transition and the circadian clock system in plants[5,13,14]. Arabidopsis cry[2] mutant exhibits a late-flowering phenotype under long day (LD) conditions rather than short day (SD) conditions[17], which infers that CRY2 can sense the inductive photoperiod signals to regulate the floral transition in Arabidopsis. PsCRY1 in pea has a slight inhibitory function on flowering, while phyacry[1] in pea shows a distinct late-flowering phenotype[22], indicating that PsCRY1 regulates floral transition in the presence of other photoreceptors, such as PsPHYA
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