FTIP1 Is an Essential Regulator Required for Florigen Transport

Lu Liu,Xingliang Hou,Zhen Tao,Chang Liu,Lisha Shen,Hao Yu,Yue Wang,Wanyan Xi,Ottoline Leyser

doi:10.1371/journal.pbio.1001313

Lu Liu, Xingliang Hou + Show 7 more

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https://doi.org/10.1371/journal.pbio.1001313

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Abstract

Author SummaryThe transition to flowering is the most dramatic phase change in flowering plants and is crucial for reproductive success. Such a transition from vegetative to reproductive growth is controlled by seasonal changes in day length. Studies originally performed in the 1930s were the first to suggest that day length is perceived by a plant's leaves; by contrast, flower formation takes place in the shoot apical meristem (the tip of the shoot that gives rise to plant organs, such as leaves and flowers). The term “florigen” was later proposed to describe a mobile floral stimulus that moves from leaves to the shoot apical meristem to induce flowering. It is only recently that FLOWERING LOCUS T (FT) in Arabidopsis, and its orthologs in various other plant species, was identified as being florigen, but how florigen is transported in plants remains completely unknown. Here, we report that a novel ER membrane protein, FT-INTERACTING PROTEIN 1 (FTIP1), interacts with FT in companion cells of the phloem (a specialized type of parenchyma cell in the phloem of the plant's vascular system) and mediates FT protein movement from companion cells to sieve elements (the conducting cells of the phloem), thus affecting FT transport to the shoot apical meristem in Arabidopsis. To our knowledge, this study reveals the first regulator that is required for florigen transport and offers new insights into possible florigen transport mechanisms in other flowering plants.

Highlights

The transition to flowering, which is crucial for the reproductive success, is the most dramatic phase change in flowering plants
It is only recently that FLOWERING LOCUS T (FT) in Arabidopsis, and its orthologs in various other plant species, was identified as being florigen, but how florigen is transported in plants remains completely unknown
We report that a novel endoplasmic reticulum (ER) membrane protein, FT-INTERACTING PROTEIN 1 (FTIP1), interacts with FT in companion cells of the phloem and mediates FT protein movement from companion cells to sieve elements, affecting FT transport to the shoot apical meristem in Arabidopsis

Summary

Introduction

The transition to flowering, which is crucial for the reproductive success, is the most dramatic phase change in flowering plants. Plants are able to adjust the timing of this transition in response to environmental conditions, such as photoperiod, temperature, and availability of nutrients. Classic experiments on the photoperiodic control of flowering in various plants have demonstrated that plant response to day length begins with the perception of photoperiod in leaves, followed by the transmission of a floral stimulus into the shoot apical meristem (SAM), where flowers are generated instead of leaves Such mobile floral stimulus moving from leaves to the SAM was proposed as ‘‘florigen’’ in the 1930s [1]. Recent findings have suggested that the proteins encoded by FLOWERING LOCUS T (FT) in Arabidopsis and its orthologs in other plant species are part of the long-sought florigen [2,3,4,5,6]

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