FLC expression is down-regulated by cold treatment in Diplotaxis tenuifolia (wild rocket), but flowering time is unaffected

Jemma L Taylor,Andrea Massiah,Sue Kennedy,Yiguo Hong,Stephen D Jackson

doi:10.1016/j.jplph.2017.03.015

Jemma L Taylor, Andrea Massiah + Show 3 more

Open Access

https://doi.org/10.1016/j.jplph.2017.03.015

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Abstract

Wild rocket (Diplotaxis tenuifolia) has become a very popular salad leaf due to its peppery taste. It is part of the Brassicaceae family and thus has a high level of homology at the DNA level to other Brassica species including Arabidopsis thaliana. The vernalization and photoperiodic requirements of wild rocket have not been reported to date. Photoperiodic experiments described here demonstrate that rocket is a facultative long day plant. To investigate the vernalization requirement, both seed and young plants were given vernalization treatments at 4°C for different lengths of time. A rocket homologue of FLOWERING LOCUS C (DtFLC) was isolated and shown to functionally complement the Arabidopsis FRI+flc3 null mutant. Whilst the expression of DtFLC was significantly reduced after just one week of cold treatment, cold treatments of two to eight weeks had no significant effect on bolting time of wild rocket indicating that rocket does not have a vernalization requirement. These findings illustrate that important fundamental differences can exist between model and crop plant species, such as in this case where down-regulation of DtFLC expression does not enable earlier flowering in wild rocket as it does in Arabidopsis and many other Brassica species.

Highlights

Wild rocket (Diplotaxis tenuifolia) has increased in popularity over the last 20 years in the leafy salads market (Chun et al, 2013), in the UK alone over 80 tons of rocket is consumed per week (Gill, 2008)
There was no significant reduction in bolting time between the non-vernalized plants kept at ambient temperatures to those subjected to the different vernalization treatments (Fig. 1c)
In the 4 °C seed vernalization experiments, DtFLC expression was analyzed in the seed or seedlings collected at the end of each vernalization treatment (Fig. 4a) and the results revealed that those subjected to one week of ambient temperature conditions had a much higher level of expression than in seed subjected to the vernalization treatments

Summary

Introduction

Wild rocket (Diplotaxis tenuifolia) has increased in popularity over the last 20 years in the leafy salads market (Chun et al, 2013), in the UK alone over 80 tons of rocket is consumed per week (Gill, 2008). There are six key pathways that regulate flowering time: the photoperiodic, autonomous, vernalization, gibberellic acid, age dependent and ambient temperature pathways (Brambilla and Fornara, 2013; Fornara et al, 2010; Jarillo and Pineiro, 2011; Srikanth and Schmid, 2011). All of these pathways converge on the floral pathway integrator genes such as FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 which activate the downstream floral meristem identity genes. When flowering is induced the shoot apical meristem changes from forming vegetative tissues such as leaves to form flowers

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