| Cytoplasmic male sterility（CMS）is a maternal genetic trait encoded by mitochondrial genes and it is impossible to produce or release viable pollen grains.Ogura CMS line is controlled by mitochondrial gene orf138,which encodes a transmembrane protein that damages mitochondria and causes metabolic disorders such as adenosine triphosphate（ATP）synthesis and accumulation of reactive oxygen species（ROS）,which leads to pollen abortion.However,the mechanism of orf138 how to regulates the expression of nuclear genes and causes pollen abortion remains to be further studied.In this study,the Ogura CMS line and it is maintainer line of Chinese cabbage were taken as the research object.firstly,according the results of morphological observation,the microstructure and ultrastructure of anther and pollen development were further observed.Meanwhile,the development process of pollen was divided into early stage（tetrad to bicellular:corresponding the abortion process of Ogura CMS line）and late stage（tricellular stage:corresponding the abortion result of Ogura CMS line）.The transcriptome sequencing and some physiological indexes of the two lines were determined.The main results are as follows:Morphological observation showed that the anther color of Ogura CMS line was white,withered and indehiscent.The microstructure observation of pollen and anther development showed that the Ogura CMS line was aborted completely,and the abnormal expansion and vacuolation of tapetum led to the abnormal development of microspores in the late uninucleate stage and could not form mature pollen.Further ultrastructural observation on the process of anther and pollen development showed that the tapetum of Ogura CMS lines did not form plastids at the tetrad stage,which prevented the tapetum forming elaioplasts and lipid droplets for pollen wall development at bicellular and tricellular stages.In the end,the exine was thiner compared with maintainer line and there is none intine formed of Ogura CMS line.Transcriptome analysis showed that 14 genes related to glutathione metabolism were up-regulated in the early stage of Ogura CMS line,which was related to the protection of plants from oxidative damage.14 genes related to pectin degradation were down-regulated in the late stage of Ogura CMS line,resulting in none intine formation and anther indehiscent,which corresponds to the observation of morphology and pollen ultrastructure.Down-regulation 7 genes related to oxidative phosphorylation affected the synthesis of ATP during the whole process.The lower content of ATP led to the failure of microspore development.Visualization of genes related to the production and scavenging of ROS showed that the production related genes were up-regulated in the early stage and catalase related genes were up-regulated in the late stage.At the same time,the content of hydrogen peroxide（H2O2）and superoxide anion（O2-）in anther of Ogura CMS line were higher than that of maintainer line.The results further proved that the accumulation of reactive oxygen species was one of the reasons for the tapetum to enter the programmed cell death（PCD）in advance.To sum up,the above results indicates that the pollen abortion of Ogura CMS line was caused by the down-regulation of related genes in complexⅤcaused by mitochondrial gene orf138,resulting in the decrease of ATP synthesis and the accumulation of ROS.The insufficient supply of ATP is one of the reasons why microspores cannot form mature pollen grains.The excessive accumulation of ROS led to the tapetum degrade in advance,which makes it unable to provide the lipids needed for microspore development,resulting in thin extine developed and there is none intine formed of pollen in Ogura CMS line.At the same time,the excessive accumulation of ROS down-regulated the expression of genes related to pectin degradation,which affected the formation of intine and the anther indehiscent.Finally,the pollen development failed and the anther indehiscent. |
PDF Full Text Request