Roles And Mechanmisms Of Sucrose And Jasmonic Acid Signals In The Regulation Of Strawberry Fruit Development

The mechanism of fruit development and ripening regulation has been an important and hot issue in fruit disciplines. Over the years, many researches have been carried out on the physiological and biochemical mechanisms behind fruit development and ripening regulation. These studies had laid the basis of fruit development and ripening regualtion. According to the respiration characteristics of fruit development and ripening, fruits can be divided into climacteric fruit and non-climacteric categories. Whiel the climacteric fruit that has been well demonstrated to be controlled by the plant hormone ethylene, the machamis for the non-climacteric fruit is largely unknown. Strawberry belongs to non-climacteric fruit. Recent studies have shown that plant hormone abscisic acid (Abscisic acid, ABA) may play an important role in the regulation of strawberry fruit ripening. Neverthelss, less information is available for the deep mechims behind ABA signaling, and addiioanlly, besides ABA, whther other singals may be involved in strawbeery fruit and development is not known. Uinsg strawbeery as the research material, in the present study, strawberries as material, we have investigated the roles and mechanism of sucrose and jasmoic acid signaling in the regulation of strawbeery fruit devleopemnt and ripening. The main results and conclusions are as follows:1. With strawberry fruit development, glucose, fructose and sucrose contents were significantly increased, but changes of sucrose content and fruit development process has closer relationship. Exogenous sucrose treatment can dramatically accelerate the strawberries ripening, and sucrose structural analogues turanose treatment can also significantly promote strawberries ripening. Our further work successfully cloned7genes encoding sucrose transporter protein in strawberry fruit, namely FaSUT1, FaSUT2, FaSUT3, FaSUT4, FaSUT5, FaSUT6and FaSUT7. Studies have shown that with fruit development and ripening, FaSUTl, FaSUT2and FaSUT3expression increased, while FaSUT1gene expression increased dramatically, and is closely related with fruit development process; FaSUT4, FaSUT6and FaSUT7expression increase in pre-mature, but decrease in the fully mature fruit. Yeast loading and testing system study shows that in all seven sucrose transporter protein, sucrose uptake ratio of FaSUTl is the fastest, followed FaSUT2. Agrobacterium-mediated gene silencing and over-expression transient expression system studies showed that FaSUT1gene over-expression promotes strawberry ripening; on the contrary, FαSUTl gene silencing can delay the fruit ripening process. Consistent with this, manipulating FaSUT1gene expression can regulate a series of fruit ripening-related gene expression.Such as FaBG1, FaSPS, FaAT, FαPG1, PaAl, FaQR, FaPAL and FaPT1etc. Importantly, manipulation FaSUTl gene expression can regulate FaNCED1gene expression of a key ABA biosynthesis gene, and ABA content changes during fruit development. These results show that in the strawberry fruit, the sucrose is not only important an important factor in the composition of fruit quality, but also as a signal, through manipulating the upstream of ABA signal, plays an important role in the strawberry fruit development regulation.2. In the early strawberry fruit development, from fruit set to mid-green fruit, endogenous JA levels has decreased. Surprisingly, endogenous JA levels roses sharply from the mid-green fruit to Green and White conversion period fruit, but JA levels has begun to drop in strawberry fruit ripening. In strawberry fruit development process, unique trends of JA content mean JA may play an important role in starting strawberry fruit ripening. Exogenous JA treatment can promote strawberry fruit development and ripening process, further illustrate JA plays an important role in strawberry fruit development and ripening. In order to further reveal the mechanism of JA in regulation of strawberry fruit development and ripening, we have a RNA transcriptome analysis using mid-green fruit. The results showed that JA treatment can induce a large number of genes expression, including6806up-regulated genes,94were up-regulated more than6times,108were5times,87were4times,167were3times;6531down-regulated genes,89were down-regulated more than6times,106were5times,86were4times,192were3times. In up-regulated genes involved in cell wall metabolism and pigment metabolism genes have a significant changes, which means that JA may regulate fruit ripening through manipulation fruit softening and coloring. Further studies showed that, in many genes involved in JA bio-synthesis, such as FaLOX, FaAOS and FaAOC etc, with strawberry fruit development its expression levels have not changed significantly. However, FaOPDA1gene expression changes dramatically with fruit development its changes is related with JA content changes, implying FaOPDA1is a key enzyme of JA synthesis in strawberry fruit. Agrobacterium-mediated transient expression studies have shown that, FaOPDA1gene over-expression promotes strawberry ripening; On the contrary, FaOPDA1gene silencing delay strawberry fruit ripening. Consistent with this, FaOPDAl gene over-expression induces pigment metabolism genes expression, such as Chalcone Synthase (CHS) etc. and fruit softening genes, such as Polygalacturonase (PG), Expansion (EXP) and so on. These results above suggested that, JA plays an important role in strawberry fruit development and ripening process.3. Sucrose has been considered the structure and energy substances, and JA has been considered to be involved in disease resistance and resilience of signal substances. This is the first discovered and confirmed the sucrose and JA can be used as signal substances plays an important role in the strawberry fruit development and ripening regulation, revealing strawberry fruit development and ripening are not controlled by a single signal, but by the manipulation of multiple signaling systems together, there is a crossover between the signals, and in different fruit development stages may play a different role. This study not only greatly deepened understanding the mechanism of non-climacteric fruit development regulation (at least for strawberry fruit), in the same time, it laid an important foundation to molecular regulation of fruit development and quality improvement.