EjRAV1/2 Delay Flowering Through Transcriptional Repression of EjFTs and EjSOC1s in Loquat.

Ze Peng,Muhammad Qasim Shahid,Ling Zhang,Yunlu Bai,Xianghui Yang,Jingjing Hao,Wenbing Su,Jiangrong Peng,Yuanyuan Jiang,Yongshun Gao,Man Wang,Chongbin Zhao

doi:10.3389/fpls.2021.816086

Abstract

Most species in Rosaceae usually need to undergo several years of juvenile phase before the initiation of flowering. After 4–6 years’ juvenile phase, cultivated loquat (Eriobotrya japonica), a species in Rosaceae, enters the reproductive phase, blooms in the autumn and sets fruits during the winter. However, the mechanisms of the transition from a seedling to an adult tree remain obscure in loquat. The regulation networks controlling seasonal flowering are also largely unknown. Here, we report two RELATED TO ABI3 AND VP1 (RAV) homologs controlling juvenility and seasonal flowering in loquat. The expressions of EjRAV1/2 were relatively high during the juvenile or vegetative phase and low at the adult or reproductive phase. Overexpression of the two EjRAVs in Arabidopsis prolonged (about threefold) the juvenile period by repressing the expressions of flowering activator genes. Additionally, the transformed plants produced more lateral branches than the wild type plants. Molecular assays revealed that the nucleus localized EjRAVs could bind to the CAACA motif of the promoters of flower signal integrators, EjFT1/2, to repress their expression levels. These findings suggest that EjRAVs play critical roles in maintaining juvenility and repressing flower initiation in the early life cycle of loquat as well as in regulating seasonal flowering. Results from this study not only shed light on the control and maintenance of the juvenile phase, but also provided potential targets for manipulation of flowering time and accelerated breeding in loquat.

Highlights

Flowering is a crucial process required for reproductive success, integrating external and internal signals (Song et al, 2013)
We examined the roles of EjRAV1 and EjRAV2 in the transition from juvenile phase to reproductive phase in loquat, and investigated their functions in seasonal flowering in trees during fruit production
These genes were clustered into three clades, among which Ej00070074 and Ej00062569 were clustered with four Arabidopsis RELATED TO ABI3 AND VP1 (RAV)/TEM genes (RAV1, RAV1-LIKE, RAV2 and RAV2-LIKE), Ej00055913, Ej00028520 and Ej00016351 grouped with FaRAV5, while Ej00018657 clustered into the RAV3 clade

Summary

Introduction

Flowering is a crucial process required for reproductive success, integrating external and internal signals (Song et al, 2013) This process is energy-consuming and plants need to undergo diverse juvenile periods to accumulate sufficient reserves before flowering (Andrés and Coupland, 2012). For annual plants, such as Arabidopsis, the whole life cycle is limited to several months. As a key developmental event of a plant’s life cycle, the juvenile-to-adult transition of both annual Arabidopsis and perennial trees is regulated by gradually decreasing the miR156/157 expressions as well as increasing the expressions of its target genes encoding a set of plant specific SPL (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE) proteins (Xu et al, 2016; Jia et al, 2017). The miR156 levels would decline as the plant age increases, which elevates the expression levels of SPL transcription factors to promote flowering by inducing the expressions of floral integrator genes including FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), APETALA1 (AP1), and LEAFY (LFY) (Wang, 2014; Xu et al, 2018)

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Results

Discussion

Conclusion