VcFT-induced mobile florigenic signals in transgenic and transgrafted blueberries

Authors: SONG, GUO-QING - Michigan State University; WALWORTH, AARON - Michigan State University; LIN, TIANYI - Michigan State University; CHEN, QIUXIA - Michigan State University; HAN, XIUMEI - National Research Council - Canada; ZAHARIA, L IRINA - National Research Council - Canada; Zhong, Gan-Yuan

Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2019
Publication Date: 9/11/2019
Citation: Song, G., Walworth, A., Lin, T., Chen, Q., Han, X., Zaharia, L., Zhong, G. 2019. VcFT-induced mobile florigenic signals in transgenic and transgrafted blueberries. Horticulture Research. 6(105). https://doi.org/10.1038/s41438-019-0188-5.
DOI: https://doi.org/10.1038/s41438-019-0188-5

Interpretive Summary: Flowering is an important trait for crops. Understanding when and how a crop flowers can help develop a new cultivar for adapting to a specific growing environment. There are many genes which have been known to involve in flowering. One gene, named as FLOWERING LOCUS T (FT), can promote early flowering in annual species, but its role has not been well demonstrated in woody species. In this study, we investigated how this gene might migrate from rootstocks to scions or vice versa in grafted blueberry plants. We compared many grafts and examined whether or not a transgenic FT in scions or rootstocks could migrate. We didn't find convincing evidence of FT migration due to the very low amount of FT and the difficulty in detecting it. However, we did observe some changes of hormone content in the non-transgenic graft partners which didn't carry the transgenic FT. We hypothesize that promotion of flowering by FT could be through some hormones. This study provides an important insight into how FT promotes flowering in perennial species.

Technical Abstract: FLOWERING LOCUS T (FT) can promote early flowering in annual species, but such role has not been well demonstrated in woody species. We produced self and reciprocal grafts involving non-transgenic blueberry (NT) and transgenic blueberry (T) carrying a 35S-driven blueberry FT (VcFT-OX). We demonstrated that the transgenic VcFT-OX rootstock promoted flowering of non-transgenic blueberry scions in the NT (scion):T (rootstock) grafts. We further analyzed RNA-Seq profiles and six groups of phytohormones of leaves and roots from both NT:T and NT:NT plants. We observed content changes of several hormone metabolites, in a descending order, in the transgenic NT:T, non-transgenic NT:T, and non-transgenic NT:NT leaves. By comparing differential expression transcripts (DETs) of these tissues in relative to their control, we found that the non-transgenic NT:T leaves had many DETs shared with the transgenic NT:T leaves, but very few with the transgenic NT:T roots. Interestingly, a number of these shared DETs belong to hormone pathway genes, concurring with the content changes of hormone metabolites in both transgenic and non-transgenic leaves of the NT:T plants. Furthermore, we observed that VcFT-OX was highly expressed in the transgenic NT:T leaves, about 5000 folds higher than that in non-transgenic NT:NT leaves. In contrast, no significant accumulation of VcFT-OX was observed in the non-transgenic NT:T leaves and transgenic NT:T roots, although many DETs were found in the two tissues, especially in the transgenic roots. These results suggest that phytohormones induced by VcFT-OX in the transgenic leaves might serve as part of the signals transmitted to both non-transgenic NT:T leaves and transgenic roots, thus resulting in early flowering and other changes in the non-transgenic NT:T scions.