Preliminary Study On The Molecular Mechanism Of Pear Cyc And CDK Genes In Regulating Fruit Size

In this paper,seven different pear varieties ’Dangshansuli’,’Xueqing’,’Housi’,Huanghua’,’Daguohuanghua’,’Aikansui’ and ’Cuiguan’ fruits were used as research materials.The relationship between the size of pear fruit and the characteristics of pulp cells was studied by investigating the growth of pear fruit in the field and making paraffin sections to observe the dynamic changes of pulp cells.The bioinformatics method was used to identify and analyze the cyclin Cyc and cyclin-dependent kinase CDK gene families in the regulation of cell cycle in pear trees.The main results are as follows:1.Dynamic study on the development of pear fruit and its changes in pulp cellsIn order to study the actual changes of different varieties of pear fruit,investigate the growth and development of seven pear fruits in the field.The results showed that the seven pear fruits began to expand gradually from 30 days after flowering,the weight and volume of the fruit increased rapidly,and the shape of the fruit changed from round to flat.Due to the different maturity stages of the seven pear fruits,there is a certain difference in the period of fruit enlargement.The fruit of ’Aikansui’ ended its expansion in 113 days after flowering;the fruit of ’Cuiguan’ ended its expansion in 122 days after flowering;the fruit of’Xueqing’ ended its expansion in 130 days after flowering;the fruit of ’Daguohuanghua’ended its expansion in 136 days after flowering;the fruits of ’Housi’ and ’Huanghua’ ended its expansion in 150 days after flowering;’Dangshansuli’ matured at the last,and the fruit ended its expansion in 174 days after flowering.At the end of fruit enlargement,there were no significant differences in the transverse diameter,longitudinal diameter,single fruit mass,fruit volume and pulp volume of other pear fruits except ’Aikansui’ and ’Dangshansuli’.In order to study the dynamic changes of pear pulp cells during fruit enlargement,seven kinds of pear pulps were used as materials to make paraffin sections for observation.The results showed that from 30 days after flowering,the pulp cells of the seven pear fruits almost ended their division and began the process of cell expansion.There was no significant difference in the final size of plup cells of seven pear fruits except ’Aikansui’ and’Housi’.The pulp cell of ’Cuiguan’ fruit was the smallest,which only expanded about 3 times;the pulp cell of ’Daguohuanghua’ fruit expanded about 5 times;the pulp cell of’Aikansui’ fruit expanded about 7 times;the pulp cell of ’Xueqing’ and ’Dangshansuli’ fruit expanded about 9 times;the pulp cell of ’Huanghua’ fruit expanded about 10 times;the pulp cell of ’Housi’ fruit was the largest,which expanded about 16 times.Further statistics on the total number of pulp cells in the pulp section of the longitudinal section of pear fruit showed that the total number of pulp cells only increased in the early to mid-fruit expansion,and then remained stable,and there was no significant difference in the total number of pulp cells in the longitudinal section of different varieties of pear fruit.In the process of increasing the weight and volume of pear fruit,the pulp cells of pear fruit mainly underwent the process of cell expansion,and the number of pulp cells did not change significantly.Therefore,the size of pulp cells is the dominant factor of fruit size.2.Identification and expression analysis of cyclin Cyc gene family in pearThis study identified 205 cyclin Cyc genes in six fruit trees of pear,papaya,citrus,peach,strawberry and grape.Among them,there are 59 Cyc genes in pear,which contain the cyclin_N or cyclin_C conserved domain of cyclin,and are unevenly distributed on 12 chromosomes.The phylogenetic tree showed that pear Cyc family genes could be divided into 7 subfamilies:CycA,CycB,CycC,CycD,CycT,CycSDS and CyJ18.The analysis of the expression of this family gene during the growth and development of ’Housi’,’Cuiguan’,’Xueqing’ and ’Dangshansuli’ fruits showed that PbCyc3,PbCyc9,PbCyc10 of the CycT subfamily;PbCycl9,PbCyc23,PbCyc33 of the CycD subfamily;PbCyc35 and PbCyc57 of the CycB subfamily;PbCyc36 of the CycA subfamily played a major role in the cell cycle regulation of pear fruit.Among them,the expression level of PbCyc3 in ’Housi’,’Cuiguan’and ’Xueqing’ fruits had a significant correlation with the developmental indexes of three pear fruits.3.Identification and expression analysis of cyclin-dependent kinase CDK gene family in pearThis study identified 100 cyclin-dependent kinase CDK genes in six fruit trees of pear,papaya,citrus,peach,strawberry and grape.Among them,there are 29 CDK genes in pear,which contain the Pkinase conserved domain of cyclin,and are unevenly distributed on 10 chromosomes.The evolutionary analysis of the CDK genes of six fruit trees,pear,strawberry,peach,grape,papaya and citrus showed that 79 gene pairs were identified,the evolutionary process of the gene was found to be conservative,and the evolution process was mainly selected by purification.The phylogenetic tree showed that pear CDK family genes could be divided into 5 subfamilies:CDKC,CDKD,CDKE,CDKG and CDKL.The analysis of the expression of this family gene during the growth and development of ’Housi’,’Cuiguan’,’Xueqing’ and ’Dangshansuli’ fruits showed that PbCDK4,PbCDK6,PbCDK8,PbCDK9,PbCDK13,PbCDK26,PbCDK27 of the CDKL subfamily;PbCDK10,PbCDK19 of the CDKG subfamily;PbCDK17 of the CDKE subfamily;PbCDK18 of the CDKC subfamily play a major role in the cell cycle regulation of pear fruit.Among them,the expression levels of PbCDK17 and PbCDK18 in ’Housi’,’Cuiguan’ and ’Xueqing’ fruits had a significant correlation with the developmental indexes of three pear fruits.The expression level of PbCDK19 in ’Dangshansuli’ fruit also had a significant correlation with the developmental indexes of the fruit.