Cloning And Analysis Of Fruit Size Related Gene AcMED25from Kiwifruit(Actinidia L.)

Kiwifruit known as "king of fruits", is one of people’s favorite fruits because of its high content of vitamin C and dietary fiber. It is one of the fruits with distinct tastes and high nutritional value and good economic benefit. As a newly-developing fruit tree, kiwifruit has good prospects, and is developing rapidly in recent years. Although China is the world’s largest producer of kiwifruit, one of the key factors that affect the industry development is the low quality of fruit. While fruit size is an important trait of its quality. In plants, mediator complex plays important roles in development process and metabolic pathways, such as organ development and flowering time and stress resistance. This experiment aims to explore the molecular mechanism of fruit growth and fruit size control in kiwifruit, started from cloning genes related to organ size regulation, combined with the artificial regulation of fruit growth, so as to provide theory basis for breeding large fruit with high quality in kiwifruit, and overcoming the adverse factors that restricting the development of its industry. And this study has the kiwifruit’Jinshuo’(Actinidia deliciosa var.’Jinshuo’) as material, and their fruit growth is promoted or limited with artificial treatment methods. RT-PCR and RACE technology were applied to clone kiwifruit MED25gene. The expression of kiwifruit MED25was analyzed by real-time PCR (qRT-PCR), to ascertain its relationship with fruit growth and size. The main results are as follows.751bp sequence of kiwifruit MED25was obtained by e-clone first based on the sequence of MED25have known in Arabidopsis thaliana, tomato, cucumber, wheat. Then specific primers were designed, and obtained221bp and267bp and516bp3fragments through RT-PCR. And by the using of RACE technology, we get2060bp cDNA of kiwifruit MED25, including5’full length cDNA. We named the2060bp cDNA as AcMED25. Homology analysis turns out that, AcMED25has the identity of65%-79%with MED25in other species. According to the bioinformatics analysis, AcMED25contains the MED25-vWA conserved domain. AcMED25may encode a fat soluble hydrophobic protein, it has multiple phosphorylation sites, and it is most likely subcellular localizated in cell nucleus. Tissue specificity analysis finds out that, AcMED25is expressed in flower and stem and leaf and fruit, which has the same character with MED25of Arabidopsis thaliana.The fruits with CPPU treatment increased by60.0%in weight and14.0%in longitudinal diameter and16.0%in wide diameter and13.8%in thick diameter respectively, compared with CK. The fruits under the condition of1/2leaf/fruit and girdling were smaller, and so is the fruits even applied additional CPPU, the fruit weight is1/3of CK’, and the longitudinal diameter is24.5%and wide diameter21.9%and thick diameter25.2%of CK’respectively.The kiwifruit increased its fruit size is mainly by increasing the inner pericarp and the central core when treated with CPPU. While girdling treatments can get small fruit whose out pericarp, inner pericarp and the central core all are smaller. CPPU may increase the out pericarp by increasing its cell size and the inner pericarp mainly by its big cell’s elongation and slightly by the small cell size increasing, and the central core also is by increasing the cell size. The fruit with girdling treatment has smaller cell, and it may be the main reason why the fruit is small.The AcMED25expression levels in untreated fruits were low (the relative level is under1) during rapid growth time of fruit (25-30days after anthesis), while the fruits treated with CPPU (Promoting the fruit growth) were extra-low (the relative level is under0.2) and those were higher (the relative level is above1) in the girdling (inhibitting the fruit growth) treatments. The expression of AcMED25at the rapidly fruit growth time (about25-30days after anthesis) may closely related to the fruit size in kiwifruit.It is a contrary tend in AcMED25expression (’low-high-low-high’) and fruit growth rate (’high-low-high-low’) and fruit weight growth (’fast-slow-fast-slow’) during the progress of fruit growth. It is possible that AcMED25may have negative function in fruit growth and regulation of fruit size. And AcMED25expression levels durring the fruit rippen time are relatively high.