The Differential Analysis Of The Contents Of IAA And Expression Of EXP In The Exocarp Of 'Dangshansuli' (Pyrus Bretschneideri Rehd.) And Its Russet Mutant

‘Dangshansuli'(Pyrus bretschneideri Rehd.)is an important and popular fruit in China,which has a high position in the pear production in China.‘Dangshansuli' pear fruit has a green yellow skin,while its mutant ‘Xiusu' pear has a russet fruit skin.To explore the role of expansin and indole-3-acetic acid(IAA)in the formation of ‘Xiusu' russet skin,in this paper,then the exocarps of ‘Dangshansuli' and ‘Xiusu' in different growth period as the experimental material.Firstly,the longitudinal diameter and transverse diameter of five layer cells under the wax layer were measured in the exocarp of ‘Dangshansuli' and‘Xiusu' with optical microscope.Secondly,the IAA content in the exocarps of‘Dangshansuli' and ‘Xiusu' were also measured using high performance liquid chromatogra PHy(HPLC).Thirdly,the expressions of eight expansin genes are explored by the real-time reverse transcription-quantitative polymerase chain reaction(RT-PCR).Then the exocarps of ‘Xiusu' treat with exogenous IAA,IAA transport inhibitor NPA and IAA synthesis inhibitors AVG,and the exocarps of ‘Xiusu' after these treatment as the test materials.The IAA content and differential expressions of two key genes(PbEXP3 and PbEXP7)are explored.Finally,the bioinformatics analysis of expansins had done to have a more particular knowledge of expansins in the pear genome,The results were as follows:(1)In this paper,the 41 expansins were searched,and were divided into 4 subtribe.The PHylogenetic tree of expansin genes in pear,the conserved structural of expansins and the exon–intron compositions of pear expansin show that expansin genes family in pear's evolution is relatively conservative.The synteny related to expansins in pear and the chromosomal mapping demonstrated that tandem and segmental duplications played critical roles in the expansion of expansin genes family,segmental duplications contributed more than tandem duplications.(2)There are obvious differences about the content of IAA in the exocarp of‘Dangshansuli' and ‘Xiusu'.In the exocarps of ‘Dangshansuli',the content of IAA was higher at the 50 days after full bloom,and decreases gradually with the fruit development,and rapid increase at 125 days after full bloom with the maximum content.In the exocarps of ‘Xiusu',the content of IAA did not decrease with the fruit development,but that reached the highest value at the 100 days after full bloom.These indicated that the content of IAA in the exocarp of ‘Xiusu' reached the peak at first.At the 100 days after full bloom,the cells in the exocarp of ‘Xiusu' divided more rapidly,and the fruit expandsfaster.(3)Different expansins had different functions in time and space.The expression of PbEXP1 and PbEXP3 were relatively high in flesh and exocarp,but were lower in other organization;PbEXP4 almost expressed in leaf,branch,fruit stalk and exocarp;PbEXP6 has highest expression in flesh;PbEXP5 and PbEXP8 were not express in leaf and branch.The expression of PbEXP2,PbEXP4,PbEXP6 and PbEXP8 were lowest at50 or 75 days after full bloom in ‘Dangshansuli' and ‘Xiusu';The expression of PbEXP1,PbEXP3 and PbEXP7 in the exocarp of ‘Dangshansuli' were reach to the maximum at the 125 days after full bloom,while that in ‘Xiusu' was at 100 days after full bloom.(4)The result of pearson correlation coefficient of content of IAA and expression of expansins showed that the expression of PbEXP3 and PbEXP7 had positive correlation with the content of IAA,in ‘Dangshansuli' the pearson correlation were 0.237 and 0.371,respectively,while that in‘Xiusu' the pearson correlation were 0.762 and0.763,respectively,which indicated that IAA have effect on PbEXP3 and PbEXP7.(5)Exogenous IAA can promote the expression of PbEXP3 and PbEXP7,and the effect of NPA on the the expression of PbEXP3 and PbEXP7 is weaker.AVG,as IAA inhibitor,reduced the expression of PbEXP3 and PbEXP7.