- Background: Sugarcane served as the model plant for discovery of the C 4 photosynthetic pathway. - However, to date there is no information available on the genomics of MGTs in sugarcane due to the complexity of the Saccharum genome.. - MGT6, MGT9 and MGT10 weredominant genes in the MGT family and werepredicted to be located inthe chloroplast. - Of the 3 dominant MGTs, SsMGT6 expression levels were found to be induced in the light period, while SsMGT9 and SsMTG10 displayed high expression levels in the dark period. - spontaneum provided basis for the comprehensive genomic study of the entire MGT genes family in Saccharum. - The results are valuable for further functional analyses of MGT genes and utilization of the MGTs for Saccharum genetic improvement.. - Full list of author information is available at the end of the article. - 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0. - Due to its unique chemical property, Mg plays an essential role in plant growth and development, such as being the central atom of the porphyrin ring of chlorophyll, enabling plants to perform photosynthesis [2, 3], and a co-enzyme in the form of Mg 2+ -ATP complexes or acts as a cofactors for more than 300 enzymes that are involved in enzyme ac- tivation [4–6]. - One third of the tropics, or 1.7 billion hectares is acid soil [11]. - Since Mg is one of the essential macroelements in plants, deficiency of Mg causes marked inhibition of plant growth and development, including symptoms such as leaf interveinal chlorosis, particularly in mature leaves due to the high mobility of Mg in plants [9], which therefore decreases photosynthesis efficiency. - Indeed, sugarcane contributes about 80% of the world sugar and about 40% of ethanol production worldwide. - To date, our understanding of the regulatory mechanism in response to Mg stress and MGT in Saccharum remains very limited due to lack of reference genome in the past.. - Open reading frame of the SsMRS2/MGTs were analyzed based. - Using the WoLF PSORT program, 8 of the SsMGT proteins were predicted to be located in chloroplasts, the remaining 2 SsMGT proteins were predicted to be localized in the mitochondria (SsMGT3) or plasma membrane (SsMGT5) (Table 2), indicating that these SsMGTs mainly play a role in the chloroplasts to. - The analysis of the TM domain revealed that 9 of the SsMGTs, ex- cept SsMGT10, contained 9 protein TM domains near their C-terminal ends, which were similar to the CorA/. - Phylogenetic analysis of SsMGTs and other plant MGTs To analyze the phylogenetics of the MGT gene family, a total 149 MGTs from 16 representative plant species and 2 species as outgroups (Chlamydomonas reinhardtiianddu- naliella salina) were used to construct the phylogenetic tree using the Neighbor-Joining and Maximum Likelihood method (Fig. - The distribution of MGT gene numbers of the examined species showed that the ancient WGD did not contribute to the expansion of the MGT gene fam- ily (Fig. - Moreover, all 5 clades contained MGT genes from the 12 representative angiosperms plants, suggesting that MGT genes from each of the 5 clades appeared before the emer- gence of angiosperms. - Exon/intron organization of the SsMGTs family and MGTs in other plant species. - In the examined plant species, the gene structure of MGTs varied in both exon number and size. - To investi- gate the structural characteristics and evolution of the MGT genes in different species, we analysed the gene features and patterns of the MGTs (Fig. - The exon number of MGTs ranged from 1 to 20 with an average about 7 (Additional files 8 and 9), and 103 of the 149 MGTs have exon numbers ranging from 4 to 6. - 1 Multiple protein sequence alignment of the SsMGT family was performed using by DNAMAN software. - Each of the subgroups had a similar exon number except for Ananas comosus.. - More- over, the SsMGTs gene structure showed a pattern similar to SbMGTs and ZmMGTs from the same clade, suggesting the conservatism of the MGT gene structure in the Pani- coideae. - In clade B, MGTs exon number ranged from 4 to 7, The first exon and second intron of SsMGT5 is larger than that of SbMGT5, which indicated an expansion and exonization of the second intron. - 2 The non-synonymous (Ka) and synonymous (Ks) substitution ratios of the 10 pairs of orthologous MGTs genes from sorghum and sugarcane were calculated by the easy_kaks calculate program. - offici- narum than in the S. - spontaneum, and higher in the leaf than in the stem. - In leaf tissue, MGT9 expression levels were observed to de- crease gradually during the development of the Sacchar- umspecies, and MGT9 likely functions in the seedling period of sugarcane development. - In contrast to MGT5 and MGT9, MGT10 was abundant in the examined tissues and presented higher expression levels in mature stems than in other tissues.. - The expression of MGT10 was suppressed in the stem tissue. - Expression pattern of MGTs during the circadian rhythms Since Mg is the central element in chlorophyll [3] and the plantsphotosynthetic apparatus is regulated by the circadian clock at the transcriptional level [39], we performed gene ex- pression analysis for MGT during the diurnal cycles in the 2 Saccharum species.MGT9 and MG10 were observed to have a peak expression in the middle of the night period in S.. - In con- trast, the dominant MGT6 displayed a diurnal expression pattern with peak levels in the middle of the day in both of the 2 analyzed Saccharum species, suggesting MGTs correl- ate with diurnal rhythms in Saccahrum (Fig. - Expression pattern of MGTs in different developmental gradient of the leaf. - To further understand the functional divergence for photosynthesis, we exploited the continuous developmen- tal gradient of the leaf transcriptome of MGTs in maize, rice and 2 Saccharum species (Fig. - levels in all the examined segments of the leaf tissues (Fig.. - The expression of MGT3 and MTG5 gradually in- creased from the base to the tip of the leaf in S. - MGT10 displayed grad- ually increase expression from the base to the tip of the leaf in both of the 2 analyzed Saccharum species.. - The MM281 cells do not survive in the low-Mg medium (<. - Based on comparative genomics and gene expres- sion patterns of the MGT families, gene evolution andtheir potential function divergence for photosyn- thesis wereinvestigated to further understand the mech- anism of MGT in Saccharum.. - Three ancient WGD events (τ, σ and ρ) occurred before the emergence of the Poaceae lineage. - The gene number of the 5 clades were similar among the 14 representative plant spe- cies despite the different ancient WGD events that oc- curred in these plant species, suggesting that gene expansion of MGT in angiosperm was not caused by an- cient WGD events. - thaliana and lineages of Poaceae, which were mainly due to the gene functional redundancy of the MGT family as the multiple LCA existed before these WGD events. - The di- vergence of 5 clades of the MGT gene family was esti- mated using the Ks in this study (Tables 3 and 4), and the results suggested that the MGT families in angiosperms (about 142~237 Mya) probably occurred before σ WGD in angiosperm (about 130 Mya) and after ε WGD in gymnosperm (about 245 Mya) [49].. - By using more representative phylogenetic position for MGT family analysis, we were able to estimate the evolu- tionary history of the clades in duplicated descending order, clade A, clade D, clade E, clade B, and clade C. - functional constraint of the orthologous genes.The genes in clade A contained more exons than other clades (Additional file 8). - According to phylogeny relationship, Clade A belong to the older group of the MGT families.. - ‘introns-early’ theory during the lengthy evolutionary process [53, 54].Consequently, we assumed that the evolu- tion of gene structures of MGTs in clade A were mainly derived by the spitted of exon [55].In Saccharum, MTG9 was one of the MGTs with highest expression levels in functional photosynthesis region, the maturing zone of leaf (Fig. - 5b) and had peak expression in the middle of the night period in S. - Suggesting that MGT9 may involve in the crosstalk of the gene network in response to the two hormones (Additional file 14). - In Saccahrum, MGT4 and MGT5 were lowly expressed in the examined tissues and MGT5 had higher expression levels than MGT4. - However, in sorghum, SbMGT4 and SbMGT5 were highly expressed in the 2 reproductive parts of the pistil and anther, re- spectively (Additional file 17) [57]. - These results may be caused by gene function redundancy be- cause of the recent ρWGD. - MGT10 was one of the most abun- dant genes, and its expression was repressed during the. - It is inter- esting that the gene expression correlates with the evolutionary history of the 4 MGTs in Saccharum, as demonstrated by the results that rank the expression levels as SsMGT10 >. - In clade D, SsMGT7 and SsMGT8 originated from the LCA of the second-round gene duplication in angiosperms by a recent gene duplication event which occurred after the divergence of monocots and dicots. - MGT3 presented higher expression levels in leaves and mature stems (sink tissues) at the mature stage than that in the young tissues, in S.officinarum than in the S. - spontaneum, and in leaf than in the stem. - Magnesium concentrations of the chloroplast matrix in the light period were higher than in the dark period [90]. - MGT5 and MGT9 had higher expression level in leaf than in the stems and root. - These exonization were predicted to located in the non-conserved regions of the MGTs, thus may not have strong effect on the functional divergence. - In clade E, SsMGT6 was the single gene retained from the common third round of gene duplication event of the MGT families (Fig. - L., Mg concentration in stroma was observed to be markedly higher in the light period than in the dark period [59]. - In this research, we identified ten SsMGTs in the mono- ploid genome of Saccharum spontaneum. - Three MGTs, MGT6, MGT9 and MGT10, weredo- minantly expressed among the MGT families in the tissues of Saccharum. - MGT6’s gene expression was induced in the light period in S. - officinarum, while, MGT9 and MTG10 displayed higher expression levels in the dark period in S. - Our study provides the foundation work for the fu- ture study of the MGT gene family to characterize the physiological role and molecular mechanisms leading to photosynthesis in sugarcane. - Similarly, both LAPurple and SES208 were used for the developmental gradient of the leaf experiment. - Tissues were collected from 11-day-old second leaves of the Sac- charum plants, and 15-day-old second leaves of LApur- ple after planting 3 h into the light period. - Stem and leaf tissues from the seedlings of the two-sugarcane species were collected from 35-day-old plants [63].. - Putative members of the MRS2/MGT gene family in the sorghum genome were identified using the BLASTP pro- gram from the Phytozome V12.1 [69], with Arabidopsis and rice MRS2/MGT protein sequences as queries. - The CDS sequences of the MGT genes were translated into protein sequences by the ExPASy Translate tool [70]. - The isoelectric point and relative molecular mass of the proteins were predicted using ExPASy Compute pI/Mw tool [73]. - The evolutionary distances were computed using the Poisson correction method [79] and were in the units of the number of amino acid substitutions per site. - Analysis of the expression profile of MGTs in Saccharum based on RNA-seq. - Positive clones were then used in an LR clonase reaction for re- combination into the pMDC84 destination vector, which contains two copies of the 35S promoter [85]. - The consistency of the melting curve demonstrated the reliability of RT-qPCR results. - Additional file 7: A schematic diagram for the relationship of the 5 clades of the phylogenetic tree constructed by NJ method. - Additional file 9: The proportion of the same number of exons in all MGTs. - Additional file 16: Complementation of the MM281 mutant by SsMGT3.. - These funding bodies had no role in the design of the study, collection, analysis, and interpretation of data, or in writing the manuscript.. - MH379211-MH379220.The S. - Magnesium transport and function in plants: the tip of the iceberg.. - Transport of magnesium and other divalent cations: evolution of the 2-TM-GxN proteins in the MIT superfamily. - Sequence and topology of the CorA magnesium transport systems of Salmonella typhimurium and Escherichia coli. - Expression and functional analysis of the CorA-MRS2-ALR-type magnesium transporter family in rice. - Identification, and functional and expression analyses of the CorA/MRS2/. - Complete nucleotide sequence of the sugarcane (Saccharum officinarum) chloroplast genome: a comparative analysis of four monocot chloroplast genomes.. - Allele-defined genome of the autopolyploid sugarcane Saccharum spontaneum L. - The research development of the response mechanisms to magnesium stresses in plants. - Systems analysis of the responses to long-term magnesium deficiency and restoration in Arabidopsis thaliana. - Comparing sequenced segments of the tomato and Arabidopsis genomes: large-scale duplication followed by selective gene loss creates a network of synteny. - Reference genome sequence of the model plant Setaria. - Evolution and expression of the fructokinase gene family in Saccharum.. - New insights into the evolution and functional divergence of the SWEET family in Saccharum based on comparative genomics. - The developmental dynamics of the maize leaf transcriptome. - Evidence of a low stromal Mg2+ concentration in intact chloroplasts in THE dark: I
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