Screen Of Genes Related To Ethylene During Fruitlet Abscission Induced By Starvation Stress In Litchi

Litchi(Litchi chinensis Sonn.),belongs to Sapindaceae family,litchi genus,and originated in Southern China,produce delicious and nutritional fruits.Though litchi trees produce many flowers and fruitlets,most of the fruitlets will drop during development.So heavy physiological fruitlets abscission will lead to low fruit production,which seriously limits litchi industry development.Ethylene,as an important plant hormone,plays a crucial role in regulating litchi fruitlet abscission,but the mechanism of how it acts is still unknown.Here,based on the litchi genome database,all of genes related to ethylene were screened through homologue searching first.Then we used girdling plus defoliation(GPD)to induce fruitlets abscission of 'Huaizhi',and the rate of ethylene production,the transcription level of the genes related to ethylene synthesis,ethylene signal transduction and ethylene response were determined during this process.Finally,the candidate genes involved in fruitlet abscission were identified.This work will provide a certain theoretic basis for exploring the mechanism of how ethylene regulate litchi fruitlet abscission.The main results are as follows:1.Field experiments showed that girdling plus defoliation(GPD)induced fruitlet abscission and the rate of ethylene release significantly.Supplementary physiological experiments showed that after GPD treatment,ACC content also increased significantly.2.According to the conserved domains of each gene family,there are 68 genes related to ethylene were screened from the litchi genome.By phylogenetic analysis a total of 10 genes(LcACS1,LcACS7,LcACO1,LcACO2,LcETR1, LcETR2A,LcETR2 B,LcERS1,LcEIN4,and LcCTR1)have evolved relationships with genes related to abscission in other species.3.qRT-PCR profilling indicated that 25 genes related to ethylene were differentially expressed in abscission zone and pericarp,24 up-regulation genes(LcACO1?LcACO2?LcACS2;LcETR2B?LcERS1?LcEIN4?LcCTR1?LcEIN2 ? LcEIL2 ? LcEIL3 ? LcERF-B1-9 ? LcERF-B2-1 ? LcERF-B3-1 ?LcERF-B3-2?LcERF-B3-4?LcERF-B3-11?LcERF-B3-12?LcERF-B3-13?LcERF-B4-1 ? LcERF-B4-2 ? LcERF-B4-3LcERF-B5-1 ? LcERF-B6-4 ?LcERF-B6-5)and 1 down-regulation genes(LcETR2A).Suggesting that these genes likely involved in the regulation of litchi fruitlet abscission.