GhLUX1 and GhELF3 Are Two Components of the Circadian Clock That Regulate Flowering Time of Gossypium hirsutum.

Pengbo Hao,Aimin Wu,Shuxun Yu,Pengyun Chen,Hengling Wei,Liang Ma,Hantao Wang

doi:10.3389/fpls.2021.691489

Abstract

Photoperiod is an important external factor that regulates flowering time, the core mechanism of which lies in the circadian clock-controlled expression of FLOWERING LOCUS T (FT) and its upstream regulators. However, the roles of the circadian clock in regulating cotton flowering time are largely unknown. In this study, we cloned two circadian clock genes in cotton, GhLUX1 and GhELF3. The physicochemical and structural properties of their putative proteins could satisfy the prerequisites for the interaction between them, which was proved by yeast two-hybrid (Y2H) and Bimolecular Fluorescent Complimentary (BiFC) assays. Phylogenetic analysis of LUXs and ELF3s indicated that the origin of LUXs was earlier than that of ELF3s, but ELF3s were more divergent and might perform more diverse functions. GhLUX1, GhELF3, GhCOL1, and GhFT exhibited rhythmic expression and were differentially expressed in the early flowering and late-flowering cotton varieties under different photoperiod conditions. Both overexpression of GhLUX1 and overexpression of GhELF3 in Arabidopsis delayed flowering probably by changing the oscillation phases and amplitudes of the key genes in the photoperiodic flowering pathway. Both silencing of GhLUX1 and silencing of GhELF3 in cotton increased the expression of GhCOL1 and GhFT and resulted in early flowering. In summary, the circadian clock genes were involved in regulating cotton flowering time and could be the candidate targets for breeding early maturing cotton varieties.

Highlights

Floral transition under favorable circumstances is necessary for the reproductive success of most plant species
The coding sequences of GhLUX1 and GhELF3 cloned from CCRI50 and GX11 were same to those cloned from TM-1, suggesting that the protein functions of GhLUX1 and GhELF3 might be unchanged in different cotton varieties
We report that two components of the circadian clock in cotton, GhLUX1 and GhELF3 participate in flowering time regulation by affecting the transcription of GhCOL1 and GhFT (Figure 6)

Summary

Introduction

Floral transition under favorable circumstances is necessary for the reproductive success of most plant species. Changes in day length (photoperiod) are reliable environmental signals that can be monitored by plants to ensure the proper flowering time (Song et al, 2013; Shim et al, 2017). The photoperiodic flowering pathway can be divided into three domains: light input, Flowering Regulation by Circadian Clock circadian clock, and output. CONSTANS (CO), the key activator of FLOWERING LOCUS T (FT), is regulated by both light signaling and the circadian clock. The circadian clock restricts CO transcription to late afternoon and night. In long days (LD), CO protein is stabilized by the light of late afternoon and activate the transcription of FT, In short days (SD), CO protein is degraded at night and FT transcription can’t be activated, which leads to late flowering (Kinmonth-Schultz et al, 2013)

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Conclusion