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. 2020 Apr 3;20(1):136.
doi: 10.1186/s12870-020-02372-w.

Flowering in Persian walnut: patterns of gene expression during flower development

Amin Hassankhah  1 , Majid Rahemi  2 , Hossein Ramshini  3 , Saadat Sarikhani  4 , Kourosh Vahdati  5
Affiliations

Flowering in Persian walnut: patterns of gene expression during flower development

Amin Hassankhah et al. BMC Plant Biol. .

Abstract

Background: Flower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT, SOC1, CAL, LFY and TFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy.

Results: The results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of the FT gene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). Like FT, the expression of SOC1 gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May). LFY and CAL genes as floral meristem identity genes are activated by FT and SOC1 genes. In contrast with flowering stimulus genes, TFL1 showed overexpression during winter dormancy which prevented flowering.

Conclusion: The expression of FT gene activated downstream floral meristem identity genes including SOC1, CAL and LFY which consequently led to release bud dormancy as well as flower anthesis and induction. Also, TFL1 as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reduced TFL1 gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.

Keywords: Anthesis; Dormancy; Expression; FT; Flower; Gene; Induction; Initiation; Persian walnut; TFL1.

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Conflict of interest statement

The authors declare that they have no competing interests. The last author is an associate editor of BMC Plant Biology. The last author had no role in the editorial process.

Figures

Fig. 1
Fig. 1
Expression levels of flowering genes in walnut terminal buds (a: FT gene; b: SOC1 gene; c: CAL gene; d: LFY gene; e: TFL1 gene)
Fig. 2
Fig. 2
Heatmap cluster of the studied gene expression involved in walnut flowering
Fig. 3
Fig. 3
A simplified model of pathway controlling walnut flowering time based on Arabidopsis flowering pathway. The scheme shows the known genes involved in flowering regulation and the interactions between them and chilling requirement. FT and SOC1 overexpress and encode proteins that activate the floral meristem identity genes such as LFY and CAL which convert the vegetative meristem to floral fate. TFL1 as a flowering inhibitor gene has overexpression during the bud dormancy and its expression was decreased by meeting chilling requirement
Fig. 4
Fig. 4
A general pattern of flowering genes expression and the date of different stages of flower development in walnut; flower induction (a, b) and initiation (c) occurred in the summer of last year. Flower differentiation (d, e) and anthesis (f, g) were observed in late March to early May of the same year. Harvest date (i) was from mid to late September. The graph C shows chilling and heat requirement of walnut trees cv. Chandler. An adequate winter chill and subsequent heat accumulation increase expression of flowering gene and release dormancy
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