Jianjian Li

Centipedegrass [Eremochloa ophiuroides(Munro) Hack.], a member of the Panicoideae subfamily, is one of the most important warm-season turfgrasses originating from China. This grass has an extremely developed prostrate growth habit and has been widely used in transitional and warm climatic regions. To better understand the genetic basis of important biological characteristics, such as prostrate growth and seed yield, in warm-season turfgrasses, we present a high-quality reference genome for centipedegrass and use PacBio, BioNano, and Hi-C technologies to anchor the 867.43 Mb genome assembly into nine pseudochromosomes, with a scaffold N50 of 86.05 Mb and 36,572 annotated genes. Centipedegrass was most closely related to sorghum and diverged from their common ancestor ~16.8 Mya. We detected a novel chromosome reshuffling event in centipedegrass, namely, the nest chromosome fusion event in which fusion of chromosomes 8 and 10 of sorghum into chromosome 3 of centipedegrass likely occurred after the divergence of centipedegrass from sorghum. The typical prostrate growth trait in centipedegrass may be linked to the expansion of candidatePROSTRATE GROWTH 1(PROG1) genes on chromosome 2. Two orthologous genes ofOsPROG1,EoPROG1,andEoPROG2, were confirmed to increase the stem number and decrease the stem angle inArabidopsis. Collectively, our assembled reference genome of centipedegrass offers new knowledge and resources to dissect the genome evolution of Panicoideae and accelerate genome-assisted breeding and improvement of plant architecture in turf plants.

Background: Chloroplast (cp) genome sequence data could provide valuable information for molecular taxonomy and phylogenetic reconstruction among plant species and individuals. However, as one of the most important warm-season turfgrasses widely used in USA and China, cp genome characteristics and phylogenetic position of centipedegrass (Eremochloa ophiuroides) were poorly understood.Results: In this study, we determined the complete chloroplast genome sequences of E. ophiuroides using high-throughput Illumina sequencing technology. The circle pseudomolecule for E. ophiuroides cp genome is 139,107 bp in length, and has a typical quadripartite structure consisting of a pair of inverted repeat (IR) regions of 22,230 bp each separated by a large single copy (LSC) region of 82,081 bp and a small single copy (SSC) region of 12,566 bp. The nucleotide composition of E. ophiuroides cp genome is asymmetric with an overall A + T content of 61.60%. It encodes a total of 131 gene species, composed of 20 duplicated genes within the IR regions and 111 unique genes including 77 protein-coding genes (PCGs), 30 transfer RNA (tRNA) genes and four ribosome RNA (rRNA) genes. Analysis of the repetitive sequences revealed that E. ophiuroides cp genome contains 51 tandem repeats including 29 forward, 20 palindromic and 2 reverse repeats, and 197 simple sequence repeats (SSRs) which were mainly composed of adenine (A) and thymine (T) bases. Comparison of the E. ophiuroides complete cp genome with the genomes of other seven Gramineae species showed a high degree of collinearity among Gramineae plants. Phylogenetic analysis showed that E. ophiuroides was closely related to E. ciliaris and E. eriopoda, and was placed in a clade with the two Eremochloa species and Mnesithea helferi within the subtribe Rottboelliinae, which clarified evolutionary status of E. ophiuroides in tribe Andropogoneae and also authenticated the current taxonomy of the tribe Andropogoneae.Conclusions: The present study provides the complete structure of the E. ophiuroides cp genome, and preliminarily ascertains the phylogenetic position of E. ophiuroides in tribe Andropogonodae. This will be of value to grass taxa identification, phylogenetic resolution, population structure and biodiversity, novel gene discovery and functional genomic studies for the genus Eremochloa.

Background: Chloroplast (cp) genome sequence data could provide valuable information for molecular taxonomy and phylogenetic reconstruction among plant species and individuals. However, as one of the most important warm-season turfgrasses widely used in USA and China, cp genome characteristics and phylogenetic position of centipedegrass (Eremochloa ophiuroides) were poorly understood.Results: In this study, we determined the complete chloroplast genome sequences of E. ophiuroides using high-throughput Illumina sequencing technology. The circle pseudomolecule for E. ophiuroides cp genome is 139,107 bp in length, and has a typical quadripartite structure consisting of a pair of inverted repeat (IR) regions of 22,230 bp each separated by a large single copy (LSC) region of 82,081 bp and a small single copy (SSC) region of 12,566 bp. The nucleotide composition of E. ophiuroides cp genome is asymmetric with an overall A + T content of 61.60%. It encodes a total of 131 gene species, composed of 20 duplicated genes within the IR regions and 111 unique genes including 77 protein-coding genes (PCGs), 30 transfer RNA (tRNA) genes and four ribosome RNA (rRNA) genes. Analysis of the repetitive sequences revealed that E. ophiuroides cp genome contains 51 tandem repeats including 29 forward, 20 palindromic and 2 reverse repeats, and 197 simple sequence repeats (SSRs) which were mainly composed of adenine (A) and thymine (T) bases. Comparison of the E. ophiuroides complete cp genome with the genomes of other seven Gramineae species showed a high degree of collinearity among Gramineae plants. Phylogenetic analysis showed that E. ophiuroides was closely related to E. ciliaris and E. eriopoda, and was placed in a clade with the two Eremochloa species and Mnesithea helferi within the subtribe Rottboelliinae, which clarified evolutionary status of E. ophiuroides in tribe Andropogoneae and also authenticated the current taxonomy of the tribe Andropogoneae.Conclusions: The present study provides the complete structure of the E. ophiuroides cp genome, and preliminarily ascertains the phylogenetic position of E. ophiuroides in tribe Andropogonodae. This will be of value to grass taxa identification, phylogenetic resolution, population structure and biodiversity, novel gene discovery and functional genomic studies for the genus Eremochloa.

Centipedegrass (Eremochloa ophiuroides (Munro) Hack.) is a perennial, warm-season C4 grass species that shows great potential for use as a low-maintenance turfgrass species in tropical and subtropical regions. However, limited genetic and genomic information is available for this species, which has impeded systematic studies on the enhancement of its turf quality and resistance against biotic and abiotic stress. In this study, Illumina HiSeq high-throughput sequencing technology was performed to generate centipedegrass transcriptome sequences. A total of 352,513 assembled sequences were used to search for simple sequence repeat (SSR) loci, and 64,470 SSR loci were detected in 47,638 SSR containing sequences. The tri-nucleotides were the most frequent repeat motif, followed by di-nucleotides, tetra-nucleotides hexnucleotides, and pentanucleotides. A total of 48,061 primer pairs were successfully designed in the flanking sequences of the SSRs, and 100 sets of primers were randomly selected for the initial validation in four centipedegrass accessions. In total, 56 (56.0%) of the 100 primer pairs tested successfully amplified alleles from all four centipedegrass accessions, while 50 were identified as polymorphic markers and were then used to assess the level of genetic diversity among 43 centipedegrass core collections. The genetic diversity analysis exhibited that the number of alleles (Na) per locus ranged from 3 to 13, and the observed heterozygosity (Ho) ranged from 0.17 to 0.83. The polymorphism information content (PIC) value of the markers ranged from 0.15 to 0.78, and the genetic distances (coefficient Nei72) between the accessions varied from 0.07 to 0.48. The UPGMA-based dendrogram clustered all 43 core collections into two main groups and six subgroups, which further validated the effectiveness of these newly developed SSR markers. Hence, these newly developed SSR markers will be valuable and potentially useful for future genetic and genomic studies of E. ophiuroides.

Shotgun survey sequences of flow‐sorted individual rye chromosomes were data mined for the presence of simple sequence repeats (SSRs). For 787,850 putative SSR loci, a total of 358,660 PCR primer pairs could be designed and 51,138 nonredundant SSR marker candidates were evaluated by in silico PCR. Of the 51,138 SSR primer candidates, 1,277 were associated with 1,125 rye gene models. A total of 2,112 of the potential SSR markers were randomly selected to represent about equal numbers for each of the rye chromosomes, and 856 SSRs were assigned to individual rye chromosomes experimentally. Potential transferability of rye SSRs to wheat and barley was of low efficiency with 4.3% (2,189) and 0.4% (223) of rye SSRs predicted to be amplified in wheat and barley, respectively. This data set of rye chromosome‐specific SSR markers will be useful for the specific detection of rye chromatin introgressed into wheat as well as for low‐cost genetic and physical mapping in rye without the need for high‐tech equipment.

Based on the similarity in gene structure between rice and wheat, the polymerase chain reaction (PCR)-based landmark unique gene (PLUG) system enabled us to design primer sets that amplify wheat genic sequences including introns. From the previously reported wheat PLUG markers, we chose 144 markers that are distributed on different chromosomes and in known chromosomal regions (bins) to obtain rye-specific PCR-based markers. We conducted PCR with the 144 primer sets and the template of the Imperial rye genomic DNA and found that 131 (91.0 %) primer sets successfully amplified PCR products. Of the 131 PLUG markers, 110 (76.4 %) markers showed rye-specific PCR amplification with or without restriction enzyme digestion. We assigned 79 of the 110 markers to seven rye chromosomes (1R to 7R) using seven wheat–rye (cv. Imperial) chromosome addition and substitution lines: 12 to 1R, 8 to 2R, 11 to 3R, 8 to 4R, 16 to 5R, 12 to 6R, and 12 to 7R. Furthermore, we located their positions on the short or long (L) chromosome arm, using 13 Imperial rye telosomic lines of common wheat (except for 3RL). Referring to the chromosome bin locations of the 79 PLUG markers in wheat, we deduced the syntenic relationships between rye and wheat chromosomes. We also discussed chromosomal rearrangements in the rye genome with reference to the cytologically visible chromosomal gaps.

The ditelosomic line for the long arm of chromosome 4B (4BL) of Chinese Spring (CS) wheat is not available because it is completely male sterile. Since all deletions in the 4B short arm (4BS) cause male sterility in the homozygous condition, a male-fertility gene should be located in a distal region of 4BS. Among the selfed progeny of a hybrid between a male-sterile 4BS deletion plant (4BS-8) and a Japanese common wheat cultivar Norin 61 (N61), we obtained self-fertile 4BS-8 homozygous deletion plants. We also found fertile nullisomic-4B plants among the selfed progeny of a hybrid between a monosomic line 4B of N61 and CS. This fact suggested that N61 has a novel male-fertility gene on a chromosome other than 4B. We established a self-fertile ditelosomic 4BL line after backcrossing a fertile 4BS-8 plant to CS monotelodisomic 4BL. By cytological observation and PCR analysis using 16 SSR markers, we verified that this ditelosomic line lacked the entire 4BS arm and found that three of the markers were on 4BS. We conducted deletion mapping using three 4BS homozygous deletion lines and three 4BS-specific markers.