Re-evaluation of transcription factor function in tomato fruit development and ripening with CRISPR/Cas9-mutagenesis

Rufang Wang,Gerco C. Angenent,Eveline Carla da Rocha Tavano,Michiel Lammers,Ruud A. de Maagd,Adriana Pinheiro Martinelli

doi:10.1038/s41598-018-38170-6

Rufang Wang, Gerco C. Angenent + Show 4 more

Open Access

https://doi.org/10.1038/s41598-018-38170-6

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Abstract

Tomato (Solanum lycopersicum) is a model for climacteric fleshy fruit ripening studies. Tomato ripening is regulated by multiple transcription factors together with the plant hormone ethylene and their downstream effector genes. Transcription Factors APETALA2a (AP2a), NON-RIPENING (NOR) and FRUITFULL (FUL1/TDR4 and FUL2/MBP7) were reported as master regulators controlling tomato fruit ripening. Their proposed functions were derived from studies of the phenotype of spontaneous mutants or RNAi knock-down lines rather than, as it appears now, actual null mutants. To study TF function in tomato fruit ripening in more detail, we used CRISPR/Cas9-mediated mutagenesis to knock out the encoding genes, and phenotypes of these mutants are reported for the first time. While the earlier ripening, orange-ripe phenotype of ap2a mutants was confirmed, the nor null mutant exhibited a much milder phenotype than the spontaneous nor mutant. Additional analyses revealed that the severe phenotype in the spontaneous mutant is caused by a dominant-negative allele. Our approach also provides new insight into the independent and overlapping functions of FUL1 and FUL2. Single and combined null alleles of FUL1 and FUL2 illustrate that these two genes have partially redundant functions in fruit ripening, but also unveil an additional role for FUL2 in early fruit development.

Highlights

Tomato (Solanum lycopersicum) produces fleshy fruits, which are climacteric, i.e. displaying a burst in ethylene production during ripening
Yeast-2-hybrid protein interaction experiments showed that both could interact with RIPENING INHIBITOR (RIN), which is expressed during ripening, while FUL2 interacts with other MADS domain proteins as well[5,7]
Flowers were labelled at anthesis as 0 Days Post Anthesis (DPA) to record the time required to reach the Breaker (Br) stage, and ethylene production of fruits was measured at Breaker and Breaker + 5 days stages

Summary

Introduction

Tomato (Solanum lycopersicum) produces fleshy fruits, which are climacteric, i.e. displaying a burst in ethylene production during ripening. By using CRISPR/Cas9-mutagenesis we generated genuine knock-out mutants of AP2a, NAC-NOR, FUL1 and FUL2 (as well as the latter two combined) to further study their function in tomato fruit ripening.

Results

Conclusion