Differences Of Nuclear-cytoplasmic Interaction Of Homozygous And Heterozygous Cytoplasm-nuclear Between Cotton CMS Lines

Cotton is the world’s most important fibre crop and one of the most important oil-producing crops.However,in recent years,the comparative efficiency of growing cotton in China has been declining and the cotton industry has shrunk significantly.The creation of CMS(cytoplasmic male sterility)lines is the basis for exploiting heterosis,which is an effective way to improve the efficiency of cotton planting.However,the current exploitation of cotton hybrid advantage is dominated by CMS lines of cytoplasm originated from Haconic cotton,the cytoplasm is of single origin,and because its cytoplasmic donor is a diploid species and its nuclear donor is a tetraploid species,the cytoplasm-nuclear interactions are severely unharmonious,with significant negative effects.The only way to minimise the negative effects of cytoplasm-nuclear interaction is to select cytoplasm-nuclear homologous CMS lines that originate from the same species.However,no cytoplasm-nuclear homologous CMS germplasm has been created,and the mechanism of its occurrence is not clear.In this study,we used three cytoplasm homologous CMS lines created by our group and two cytoplasm heterologous CMS lines of our group.We comparatively studied the floral organ morphology,abortive processes,reactive oxygen species(ROS)metabolism,mitochondrial DNA(mt DNA)sequences,and transcriptomic and methylomic differences between the two and came up with the following main results:1.Morphological observations showed that there was no significant difference in plant and leaf morphology between the cytoplasm homozygous and cytoplasm heterozygous CMS lines,but the cytoplasm heterozygous CMS lines had more prominent styles,shorter filaments and drier anthers.2.Cytological observations of the abortion process showed that both abortion types were pollen-free,and their abortion occurred from meiosis to early mononuclear stage,and no degradation of the chorionic felt layer cells occurred throughout anther development,but the abortion of the cytoplasm heterologous CMS line was relatively early,and no tetrad structure was found.3.Physiological indicators related to ROS metabolism showed that the enzymatic activities of POD and CAT were lower in the tetrad to mature pollen grain period in the cytoplasm heterologous CMS lines than in the cytoplasm homologous CMS lines,while the MDA content as the end product of ROS metabolism and the enzymatic activities showed opposite performance;Since the MDA content in the maintainer lines was lower than that in the sterile lines,and the MDA content in the cytoplasm heterozygous CMS lines was higher at the tetrad stage to the mature pollen grain stage than that in the cytoplasm homozygous CMS lines,it was speculated that the high occurrence of ROS was due to cytoplasm heterogeneity.4.The mt DNA resequencing results showed that although 36 coding protein genes were predicted for each cotton material,there were differences in the number of r RNAs and t RNAs,and the number of t RNAs was higher in all the maintainer lines than in the sterile lines.In homogeneous heterogeneous systems,the number of single nucleotide polymorphism(SNP)was larger than that in cytoplasm homogeneous CMS lines,while in homogeneous heterogeneous systems,the total number of SNP was smaller than that in cytoplasm homogeneous CMS lines.It indicates that the contribution of the nuclear genome to the total SNP is greater than that of the cytoplasm in the CMS cytoplasm-nuclear interaction system.Comparing the structural variation(SV)of the genomes of five CMS lines,using the mitochondrial genomes of the maintenance lines as a reference,we found that the plasmon-nuclear heterologous CMS lines were more complex than the plasmon-nuclear homologous CMS.This indicates that cytoplasm-nuclear heterologous interactions are more likely to lead to structural variation in mt DNA.Comparing the covariance of the mitochondrial genomes of the eight test materials,it was found that the cytoplasm homologous CMS lines had a high degree of covariance with the maintenance lines,and four ORFs(orf115b,orf341 a,orf591a and orf609a)were identified as key candidates associated with CMS because they possessed the characteristics of CMS-related genes,because cytoplasm homologous CMS minimized genetic cumbersomeness beyond sterility.5.The combined whole-gene methylationome and transcriptome analysis revealed that a total of 847 differentially methylated region differentially expressed genes(DMEGs)were identified between the cytoplasm homologous CMS line 07-113 A and its maintenance line 07-113 B,and 07-113 A had a higher degree of methylation than 07-113 B.In DMEGs,hypermethylated genes were significantly enriched in the "starch and sucrose metabolism" pathway.It is hypothesized that transcriptional repression is associated with the hypermethylation of 07-113 A,which leads to down-regulation of gene expression.Changes in starch and the reduced sugar flux in its biosynthesis are also likely to lead to altered gene expression and ultimately to pollen sterility.Accordingly,five key genes that may be associated with CMS in cotton were identified,which are mainly involved in processes such as carbohydrate and energy metabolism,male gametophyte development and programmed cell death.Combining the results of the above analysis,this study showed that the system of homologous cytoplasm and its nucleus were least affected by the nucleo-cytoplasmic interaction effect and were the best combination for studying male sterility.And several key genes that may be related to CMS in cotton were identified.This study provides some evidence for the hypothesis of the molecular mechanism of cotton sterility,and will provide a theoretical basis for the creation of CMS lines optimized for cytoplasm-nucleus interactions,as well as a basis for analyzing the mechanism of cytoplasm-nucleus homozygous and cytoplasm-nucleus heterozygous CMS.