Possible Mechanism of Sucrose and Trehalose-6-Phosphate in Regulating the Secondary Flower on the Strong Upright Spring Shoots of Blueberry Planted in Greenhouse

Secondary flowering is the phenomenon in which a tree blooms twice or more times a year. Along with the development of blueberry (<i>Vaccinium corymbosum</i> L.) fruits in spring, a large number of secondary flowers on the strong upright spring shoots were noticed in blueberries planted in the greenhouse. To reveal the cause and possible regulatory mechanism of the phenomenon, we clarified the phenological characteristics of flower bud differentiation and development on the spring shoots by combining phenological phenotype with anatomical observation. Furthermore, the changes in carbohydrates, trehalose-6-phosphate (Tre6P), and the relationship among the key enzyme regulatory genes for Tre6P metabolism and the key regulatory genes for flower formation during the differentiation process of apical buds and axillary buds were investigated. The results showed that the process of flower bud differentiation and flowering of apical and axillary buds was consistent, accompanied by a large amount of carbohydrate consumption. This process was positively correlated with the expression trends of <i>VcTPS1/2</i>, <i>VcSnRK1</i>, <i>VcFT</i>, <i>VcLFY2</i>, <i>VcSPL43</i>, <i>VcAP1</i>, and <i>VcDAM</i> in general, and negatively correlated with that of <i>VcTPP</i>. In addition, there is a certain difference in the differentiation progress of flower buds between the apical and axillary buds. Compared with axillary buds, apical buds had higher contents of sucrose, fructose, glucose, Tre6P, and higher expression levels of <i>VcTPS2</i>, <i>VcFT</i>, <i>VcSPL43</i>, and <i>VcAP1</i>. Moreover, <i>VcTPS1</i> and <i>VcTPS2</i> were more closely related to the physiological substances (sucrose and Tre6P) in axillary bud and apical bud differentiation, respectively. It was suggested that sucrose and trehalose-6-phosphate play a crucial role in promoting flower bud differentiation in strong upright spring shoots, and <i>VcTPS1</i> and <i>VcTPS2</i> might play a central role in these activities. Our study provided substantial sight for further study on the mechanism of multiple flowering of blueberries and laid a foundation for the regulation and utilization of the phenomenon of multiple flowering in a growing season of perennial woody plants.