Genomic And Transcriptomic Analysis Of Fine Turf Quality Characteristics Of Bermudagrass

Cynodon dactylon L.is a perennial grass of the Cynodon genus belonging to the teff subfamily of gramineae with well-developed stolons and rhizomes.Some prostrate-growing bermudagrass germplasms have been developed as turfgrasses with many fine turf quality characteristics,including fast propagation,high density,trampling resistance,salinity resistance,drought resistance,etc.Many researches focusing on the diversity of germplasm resources,genetic diversity and stress resistance physiology of bermudagrass were successfully performed,and obtained fruitful results.However,few researches were conducted to address the important issues of growth and developmental regulation mechanisms of bermudagrass,especially the regulation mechanism of the formation of stolons and rhizomes,as well as the regulation mechanism of efficient photosynthesis and rapid growth of leaves.In this study,we successfully assembled and annotated the genome of bermudagrass cultivar ’Yangjiang’.Moreover,we performed transcriptome sequencing analysis of six different organs of the same cultivar.The results not only provide important genetic information for the subsequent basic research and molecular breeding of bermudagrass,but also lay the foundation for the in-depth study of bermudagrass morphogenesis,growth and development.The main conclusions are as follows:1.The genome of bermudagrass cultivar ’Yangjiang’ was successfully sequenced and annotated in this study.The assembled genome contains 36 chromosomes with a size of approximately 1 Gb,and 76897 protein-coding genes were functionally annotated.On this basis,comparative transcriptomic sequencing analysis was performed on six organs,including leaf,inflorescence,root,shoot,stolon and rhizome.It was found that 10 genes were stably expressed in six organs,which were possible house-keeping genes.2.Comparative genomics analysis indicated that the number of PROG1 and TAC1 associated with prostrate growth were not significantly selected in bermudagrass,however,LAZY1 gene which was associated with erect growth were negatively selected.Transcriptomic analysis revealed that many sucrose metabolism and hormone-response genes were differentially expressed in the three stems,suggesting their putative important functions in the differentiation and development of stolon and rhizome in bermudagrass.3.There are 108 genes encoding enzymes involved in different steps of C4 photosynthesis in the bermudagrass genome,among which pyruvate phosphate dikinase(PPDK)and phosphoenolpyruvate carboxylase(PEPC)participating in the CO2 fixation showed positive selection.Transcriptomic analysis further revealed that a total of six genes encoding PPDK and PEPC were highly expressed in the leaves,suggesting that they may be closely related to C4 photosynthesis.4.Comparative genomics analyses indicated that ZIP4 and other ZMM family genes involved in homologous recombination in bermudagrass showed similar gene deletion phenomena as other polyploid plants,thus ensuring the stable inheritance of the tetraploid genome.Additionally,the numbers of genes of the transcription factor families associated with abiotic stress responses were significantly increased in bermudagrass due to genomic polyploidy.Transcriptomic analysis revealed that these genes showed different expression patterns in six different organs,which might provide the genetic basis for high stress resistance of bermudagrass.In summary,the above results of this study analyzed the possible reasons how fine turf quality characteristics forms at the genome and transcriptome level,including well-developed stolons and rhizomes,efficient photosynthesis,and strong resistance to stresses,which lays a solid foundation for the subsequent breeding improvement of bermudagrass breeding.