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Control of sucrose accumulation in sugarcane (Saccharum spp. hybrids) involves miRNA-mediated regulation of genes and transcription factors associated with sugar metabolism

ABSTRACT: Sugarcane established industrial crop providing sugar, ethanol and biomass-derived electricity around the world. Cane sugar content is an important, breeding target, but its improvement remains very slow in many breeding programmes. Biotechnology strategies to improve sucrose accumulation made little progress at crop level, mainly due to the limited understanding of its regulation. MiRNAs regulate many metabolic processes in plants. However, their roles and target genes associated with sugarcane sucrose accumulation remains unknown. Here, we conducted high-throughput sequencing of transcriptome, small RNAs and degradome of leaves and stem of two sugarcane genotypes with contrasting sucrose content from the early to late stages of sucrose accumulation stages, which provided more insights into miRNA-associated gene regulation during sucrose accumulation. Transcriptome analysis identified 18,722 differentially expressed genes (DEGs) between both genotypes during sucrose accumulation. The major DEGs identified were involved in starch and sucrose metabolism, and photosynthesis etc. miRNA sequencing identified 563 known and 281 novel miRNAs from both genotypes during sucrose accumulation. Of these, 311 miRNAs were differentially expressed.752 targets of 368 miRNAs (609 targets for 260 known miRNAs and 168 targets for 108 novel miRNAs) were identified by degradom sequencing.Several known and novel miRNAs and their target genes associated with sugar metabolism, sugar transport and sucrose storage were identified in this study.This new insight into the complex network of sucrose accumulation in sugarcane will help identify candidate targets for sucrose improvement in sugarcane through molecular means.

ORGANISM(S): Saccharum hybrid cultivar

PROVIDER: GSE188303 | GEO | 2021/12/30

REPOSITORIES: GEO

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Project description:Sugarcane accumulates high concentrations of sucrose in the mature stalk, with numerous physiological processes in maturing stalk tissue both directly and indirectly involved. A considerable portion of carbohydrate metabolism is also devoted to cell wall synthesis and fibre production. Previously, we have identified differentially expressed transcripts correlated with sucrose accumulation and fibre production in various internodes of the sugarcane stalk. In this study, we have examined tissue-specific expression patterns to further explore gene pathways responsible for sucrose accumulation and fibre synthesis. We performed large-scale expression profiling of storage parenchyma, vascular bundles and rind dissected from a maturing stalk internode from field-grown commercial sugarcane harvested at 11 months of age. We identified 10 cellulose synthase subunit genes in sugarcane and examined significant differences in the expression of their corresponding transcripts and those of several sugar transporters between the different tissues. These were further correlated with differential expression patterns for transcripts of specific COBRA-like proteins and other proteins with acknowledged roles in cell wall metabolism. We found that the sugar transporters ShPST2a, ShPST2b and ShSUT4 were significantly up-regulated in storage parenchyma while ShSUT1 was up-regulated in vascular bundles. Two co-ordinately expressed groups of cell wall related transcripts were also identified. One group which is associated with primary cell wall synthesis (ShCesA1, ShCesA7, ShCesA9 and Shbk2l3) was up-regulated in parenchyma. The other group which is associated with secondary cell wall synthesis (ShCesA10, ShCesA11, ShCesA12 and Shbk-2) was up-regulated in rind. We also report an unexpected paucity in differential expression of cell wall-related genes in vascular bundles. Our results indicate that there is spatial separation for elevated expression of these important targets in both sucrose accumulation and cell wall synthesis, allowing for increased clarity in our understanding of sucrose transport and fibre synthesis in sugarcane.

Project description:Sugarcane is an economically important crop contributing to the world’s sugar and ethanol production with 80% and 40%, respectively. In recent years, the growing demands for sugar and ethanol production has prompted the necessity to increase sugarcane productivity through conventional breeding programs. However, sugarcane breeders have encountered several difficulties to raise productivity, mainly due to its complex genetics. Sugarcane has a polyploidy genome, with many varieties being aneuploidy. Today, the majority of the planted sugarcane cultivars are complex hybrids derived mainly from crosses between Saccharum officinarum and S. spontaneum. Therefore, proteomics can provide some insight into deciphering gene regulation and changes in carbon metabolism and sucrose accumulation in the culms at different stages of plant development. The aim of this work was to compare the quantitative changes of proteins in sugarcane culms, during plant growth and sucrose accumulation. Total proteins were isolated from both, juvenile and maturing internodes at three stages of plant development. Label free shotgun proteomics was used for protein profiling and quantification. The internodes 5 (I5) and 9 (I9) of 4, 7 and 10 month-old-plants (4M, 7M and 10M, respectively) were harvested and used for proteomic analyses. To mimic field conditions of sucrose accumulation during sugarcane maturation, we stopped watering 10M plants for 10 days. An average of 1130 proteins, unique and differentially expressed across all ages were identified and quantified. Proteins were categorized within 27 functional groups, related to biological process. The patterns of expression for some categories, such as cellular amino acids, metabolic processes, secondary metabolic processes and translation were down-regulated in the immature internode (I5-10M), while up-regulated in the mature I9-10M. We observed an increase in the abundance of several enzymes of the glycolytic pathway and isoforms of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC), in the juvenile stages of development of I9. These changes in enzymes contents indicates that at the early stages of internode development, hypoxia is increasing the glycolytic and ethanolic fermentation pathways, in order to supply ATP for plant growth and NAD+ for mitochondrial respiration, which might be impaired by the low oxygen availability inside the culm.

Project description:In C4 sugarcane (Saccharum spp. hybrids), photosynthetic activity has been shown to be regulated by the demand for carbon from sink tissues. There is evidence, from other plant species, that sink-limitation of photosynthesis is facilitated by sugar-signaling mechanisms in the leaf that affect photosynthesis through regulation of gene expression. In this work, we manipulated leaf sugar levels by cold-girdling leaves (5oC) for 80 h to examine the mechanisms whereby leaf sugar accumulation affects photosynthetic activity and assess whether signaling mechanisms reported for other species operate in sugarcane. During this time, sucrose and hexose concentrations above the girdle increased by 77% and 81%, respectively. Conversely, leaf photosynthetic activity (A) and electron transport rates (ETR) decreased by 66% and 54%, respectively. Quantitative expression profiling by means of an Affymetrix GeneChip Sugarcane Genome Array was used to identify genes responsive to cold-girdling (56 h). A number of genes (74) involved in primary and secondary metabolic pathways were identified as being differentially expressed. Decreased expression of genes related to photosynthesis and increased expression of genes involved in assimilate partitioning, cell wall synthesis, phosphate metabolism and stress were observed. Furthermore four probe sets homologous to trehalose 6-phosphate phosphatase (TPP; EC 5.3.1.1) and trehalose 6-phosphate synthase (TPS; EC 2.4.1.15) were up- and down-regulated, respectively, indicating a possible role for trehalose 6-phosphate (T6P) as a putative sugar-sensor in sugarcane leaves. Twelve month-old field grown Saccharum spp. (L.) hybrid cv. N19 (N19) cultivated at Mount Edgecombe, KwaZulu-Natal (SASRI) were used in the study, which was conducted in November, 2006. Plants were grown on a 5 x 15 m plot located on a north-east facing slope with a gradient of ca. 10o. Cold-girdles were attached to sugarcane leaves (n=4) for a period of 56 h prior to harvest. The girdle consisted of 0.75 cm (diameter) soft plastic tubing, firmly clamped around each leaf, approximately 30 cm from the leaf base. Cooled water maintained at 5oC was then pumped through the tubing using a Grant LTD6G cooling bath (Grant Instruments, Barrington, Cambridge, UK). At harvest, leaf samples were immediately frozen in liquid nitrogen (–196oC) and subsequently milled in an A11 Basic Analysis Mill (IKA, Staufen, Germany). Ground leaf tissue was stored at –80oC in 50 ml centrifuge tubes prior to analysis.

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Control of sucrose accumulation in sugarcane (Saccharum spp. hybrids) involves miRNA-mediated regulation of genes and transcription factors associated with sugar metabolism

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