| Camellia oleifera is an important woody edible oil oil tree species in China,but there is a serious fruit abscission in production,which leads to low yield.Our group’s preliminary research found that ethylene has an important effect on the fruit abscission in C.oleifera.However,the mechanism by which ethylene affects the fruit abscission in C.oleifera is still unclear.Therefore,this study was carried out from field observation,histological anatomy,hormone metabolism and molecular level with the national approved oil tea ’Huashuo’ as the experimental material.Firstly,the peak of fruit abscission was determined by observing the dynamic of fruit abscission during the growth and development period in the field,and the difference of abscission zone tissue structure between the abnormal fruit and the normal fruit in the peak of fruit abscission was analyzed anatomically.Second,the difference of endogenous hormone content between abnormal fruit and normal fruit,and the effect of exogenous ethylene on fruit abscission in C.oleifera were compared and analyzed.Thirdly,transcriptome analysis was conducted on normal fruits,abnormal fruit and ethephon-treated fruit to determine the key genes affecting the fruit abscission in C.oleifera,aiming to provide a theoretical basis for clarifying the effect mechanism of ethylene on the fruit abscission in C.oleifera.The main results are as follows:1.The law of fruit abscission in C.oleifera and the morphological and anatomical characteristics of fruit abscission zone.According to the investigation of fruit abscission of C.oleifera ’Huashuo’ during its fruit development,it was found that C.oleifera entered the peak of fruit abscission in late August,and the cumulative fruit dropping rate was 28.5%by early October.The results showed that there was an obvious difference in the structure between the abscission zone of abnormal fruit and normal fruit.It could be seen from the external morphology that the depression of the abnormal fruit was deeper than that of the normal fruit,and the stalk did not adhered closely with stem.The results of scanning electron microscopy showed that the pith of the proximal fracture surface of the normal fruit was more obvious than that of the abnormal fruit,and the cells were broken seriously.The results of paraffin section showed that the cortex had differentiated into abscission layer,and the cells at the edge of the isolated area had disintegrated and formed a deep depression.In contrast,the cell morphology of the abscission zone of normal fruit was normal and there was no abscission layer.2.Effects of endogenous hormones and exogenous ethylene on fruit abscission in C.oleifera.The content of endogenous hormones in the two kinds of fruit were determined.The results showed that the content of ethylene precursor ACC(1-amino cyclopropane-1-carboxylic acid)was 4,286.79 ng/g in abscission zone of abnormal fruit,which was 50.26%higher than that of normal fruit.The activity of ACO(ACC oxidase)enzyme increased by 93.98%compared with that of normal fruit,indicating that ethylene was closely related to a large amount of fruit abscission during the fruit development in C.oleifera.Exogenous spraying 2 g/L ethylene and the results showed that the cumulative abscission rate of the treatment group on the 4th(35.00%),8th(48.67%)and 16th(57.67%)day after treatment(DAT)were significantly higher than that of the control group on the 4th(4.00%),8th(7.50%)and 16th(25.00%).The ACC content and ACO enzyme activity in the treatment group is significantly higher than the control group as well.These results indicated that the increase of endogenous ethylene content in C.oleifera was closely related to massive fruit abscission during its fruit development.3.Transcriptome analysis of fruit abscission in C.oleifera.Transcriptome sequencing was performed on isolated samples of normal fruits,abnormal fruits and ethephon trated fruits.A total of 65,401,180 clean reads and 165,606 Unigenes were obtained.A total of 85,136 Unigenes were annotated to four major databases(NR,KEGG,COG and SwissProt).The analysis of differentially expressed genes showed that 1,156 genes were up-regulated and 239 genes were down-regulated in the abscission zone of abnormal fruit under natural conditions compared with that of the normal fruits.There were 776 up-regulated genes and 582 down-regulated genes in the abscission zone after 8 days of exogenous ethylene treatment compared with that of clean water treatment.There were 897 up-regulated genes and 478 down-regulated genes in the abscission zone after 16 days of exogenous ethylene treatment compared with that of clean water treatment.Seven ethylene biosynthesis and signal transduction genes(ACS1,ACO1,ACO2,ACO3,ETR1,ETR2 and ERF1)were found to be upregulated in abscission zone of abnormal fruit under natural conditions and abscission zone after 8 days of exogenous ethylene treatment,which were consistent with the results verified by qRT-PCR.These 7 genes may were the key genes in the fruit abscission in C.oleifera. |
