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

Area of Science:

• Plant Molecular Biology
• Fruit Tree Genetics
• Agricultural Science

Background:

• Walnut yield is significantly influenced by flower development and fruit set.
• Understanding flowering gene regulation in fruit trees is crucial for molecular breeding programs.

Purpose of the Study:

• Investigate the expression patterns of key flowering genes (FT, SOC1, CAL, LFY, TFL1) in Persian walnut (cv. Chandler).
• Correlate gene expression with distinct developmental stages, including growing season and winter dormancy.

Main Methods:

• Monitoring of walnut phenological stages (flower induction, initiation, differentiation, anthesis).
• Quantitative analysis of flowering gene expression (FT, SOC1, CAL, LFY, TFL1) throughout the annual cycle.
• Assessment of chilling and heat requirements for reproductive development.

Main Results:

• Walnut flower induction and initiation occurred in early June and late September, respectively.
• Flower differentiation and anthesis took place from late March to early May after meeting chilling and heat requirements.
• FT and SOC1 gene expression increased during flower differentiation, anthesis, and induction. LFY and CAL genes were activated by FT and SOC1.
• TFL1 gene showed overexpression during winter dormancy, inhibiting flowering.

Conclusions:

• FT gene expression activates downstream floral meristem identity genes (SOC1, CAL, LFY), promoting bud dormancy release, anthesis, and induction.
• TFL1 acts as a flowering inhibitor in walnut, with its overexpression during dormancy preventing flowering.
• Chilling accumulation reduces TFL1 expression and enhances flowering gene expression, facilitating dormancy release.