The Major Floral Promoter NtFT5 in Tobacco (Nicotiana tabacum) Is a Promising Target for Crop Improvement.

Florentin J Schmidt,Dirk Prüfer,Jost Muth,Sophie Lichtenauer,Lena Grundmann,Gundula A Noll,Marius M Zimmermann,Richard M Twyman,David R Wiedmann

doi:10.3389/fpls.2019.01666

Abstract

The FLOWERING LOCUS T (FT)-like gene family encodes key regulators of flower induction that affect the timing of reproduction in many angiosperm species. Agricultural research has therefore focused on such genes to improve the success of breeding programs and enhance agronomic traits. We recently identified a novel FT-like gene (NtFT5) that encodes a day-neutral floral activator in the model tobacco crop Nicotiana tabacum. However, further characterization is necessary to determine its value as a target for breeding programs. We therefore investigated the function of NtFT5 by expression analysis and mutagenesis. Expression analysis revealed that NtFT5 is transcribed in phloem companion cells, as is typical for FT-like genes. However, high levels of NtFT5 mRNA accumulated not only in the leaves but also in the stem. Loss-of-function mutants (generated using CRISPR/Cas9) were unable to switch to reproductive growth under long-day conditions, indicating that NtFT5 is an indispensable major floral activator during long-days. Backcrossing was achieved by grafting the mutant scions onto wild-type rootstock, allowing the restoration of flowering and pollination by a wild-type donor. The resulting heterozygous Ntft5–/NtFT5+ plants flowered with a mean delay of only ~2 days, demonstrating that one functional allele is sufficient for near-normal reproductive timing. However, this minor extension of the vegetative growth phase also conferred beneficial agronomic traits, including a >10% increase in vegetative leaf biomass on the main shoot and the production of more seeds. The agronomic benefits of the heterozygous plants persisted under various abiotic stress conditions, confirming that NtFT5 is a promising target for crop improvement to address the effects of climate change.

Highlights

Flowering is one of the major events in the life cycle of annual angiosperms, and the transition from vegetative to reproductive growth is an important agronomic trait in the context of plant breeding
The gene structure of NtFT5 was recently reported in N. tabacum cv
Furthering our earlier studies, here we assessed the potential of NtFT5 as target for breeding programs by investigating the expression and function of the gene in detail (Harig et al, 2012; Beinecke et al, 2018)

Summary

Introduction

Flowering is one of the major events in the life cycle of annual angiosperms, and the transition from vegetative to reproductive growth is an important agronomic trait in the context of plant breeding. The signals corresponding to these stimuli are integrated by the products of key genes such as FLOWERING LOCUS T (FT), a member of the phosphatidylethanolamine-binding protein (PEBP) family. These proteins are widely conserved regulators of developmental processes in plants and often function as activators of floral transition (Kardailsky et al, 1999; Kobayashi et al, 1999; Chardon and Damerval, 2005; Karlgren et al, 2011; Wickland and Hanzawa, 2015). The FT-FD complex activates the expression of floral meristem identity genes such as APETALA1 (AP1), leading to the development of flowers (Abe et al, 2005; Wigge et al, 2005; Corbesier et al, 2007; Mathieu et al, 2007)

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Conclusion