Expression of the kfpMYB gene and its relationship with calyx persistence in the fruits of 'Kuerlexiangli'pear

Abstract: 【Objective】'Kuerlexiangli'pear is one of the most important agricultural crops in Xinjiang.The calyx of'Kuerlexiangli'pear may be either persistent or deciduous. A persistent calyx can negatively affect fruit shape, reducing its appeal to customers. Therefore, it is of great importance to reveal the mechanism controlling the calyx persistence. The purpose of this study was to determine the correlation between kfpMYB gene expression and calyx persistence.【Methods】Flowers of'Kuerlexiangli'pear were collected in an orchard at Bagejigedai village, Korla city, Xinjiang province. The flowers were collected at the full flowering stage. In the flowering period, three'Kuerlexiangli'pear trees with strong tree potential and weak tree potential were selected, and 30 flowers of 2-5 in the strong tree and the weak tree were collected respectively. Thirty flowers were collected from each tree. After collection, the flowers were immediately frozen in liquid N and then taken to the laboratory where they werestored at-80 ℃ in an ultra low temperature refrigerator. These samples were used to measure gene expression. We also marked 100 flowers on each tree (the second, third, fourth and fifth opened flowers in the clusters) . Calyx persistence was determined a week after petal drop. Total RNA was extracted using an Aidelai kit for rapid extraction of plant RNA according to the manufacturer's directions. The concentration of total RNA was detected with a nucleic acid analyzer. The integrity of the total RNA was detected by 1% agarose gel electrophoresis. Total RNA was used as a template to synthesize the first chain of cDNA with a TakaRa Prime Script TMRT Reagent Kit according to the manufacturer's instructions.This step also included the removal of genomic DNA. The primers were designed according to cDNA sequence information of 'Kuerlexiangli' pear kfpMYB gene. The relative expression of the kfpMYB gene in the high vigor trees and the low vigor trees was determined by real-time fluorescence quantitative PCR. The data was analyzed using SPSS software.【Results】The results of real-time quantitative PCR showed that the expression of kfpMYB expression in the 2-5 opened flowers in the clusters on high vigor tree was higher than in the 2-5 opened flowers in the clusters on low vigor trees. The average relative expression quantity of kfpMYB was 1.80 on high vigor trees. The kfpMYB expressions on high vigor tree number 1, 2, and 3 were all greater than 1.80 (67, 75, and 67% respectively) . The average relative expression quantity of kfpMYB was 1.22 on low vigor trees. The expressions on low vigor trees number 1, 2, and 3 were all less than 1.80 (67, 75, and 83% respectively) . The field survey results showed that calyx persistence was significantly greater in the second, third and fourth opened flowers in the clusters than fifth opened flowers in the clusters on high vigor trees, the second, third opened flowers in the clusters than the fourth and fifth opened flowers in the clusters on low vigor trees. The rates of calyx persistence on high vigor tree numbers 1, 2 and 3 were 70, 80, and 67%, respectively. The rates of calyx persistence on low vigor tree numbers 1, 2, and 3 were 60, 63, and 75% respectively. The relative expression of the MYB gene in the high vigor trees was positively correlated with calyx persistence, whereas the relative expression of the MYB gene in low vigor trees was negatively correlated with calyx abscission.【Conclusion】The calyx of'Kuerlexiangli'pear had greater persistence when kfpMYB expression was high and less persistence when kfpMYB gene expression was low. The relative expression of kfpMYB in 4-5 opened flowers in the clusters on vigor trees was significantly higher than that in 1-2 opened flowers in the clusters on weak tree. The relative expression of kfpMYB in'Kuerlexiangli'pear at flowering stage was closely related to the abscission and persistence of calyx.