Search

Background The development of biomass crops aims to meet industrial yield demands, in order to optimize profitability and sustainability. Achieving these goals in an energy crop like sugarcane relies on breeding for sucrose accumulation, fiber content and stalk number. To expand the understanding of the biological pathways related to these traits, we evaluated gene expression of two groups of genotypes contrasting in biomass composition. Results First visible dewlap leaves were collected from 12 genotypes, six per group, to perform RNA-Seq. We found a high number of differentially expressed genes, showing how hybridization in a complex polyploid system caused extensive modifications in genome functioning. We found evidence that differences in transposition and defense related genes may arise due to the complex nature of the polyploid Saccharum genomes. Genotypes within both biomass groups showed substantial variability in genes involved in photosynthesis. However, most genes coding for photosystem components or those coding for phosphoenolpyruvate carboxylases (PEPCs) were upregulated in the high biomass group. Sucrose synthase (SuSy) coding genes were upregulated in the low biomass group, showing that this enzyme class can be involved with sucrose synthesis in leaves, similarly to sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (SPP). Genes in pathways related to biosynthesis of cell wall components and expansins coding genes showed low average expression levels and were mostly upregulated in the high biomass group. Conclusions Together, these results show differences in carbohydrate synthesis and carbon partitioning in the source tissue of distinct phenotypic groups. Our data from sugarcane leaves revealed how hybridization in a complex polyploid system resulted in noticeably different transcriptomic profiles between contrasting genotypes.

O Brasil é o maior produtor de cana-de-açúcar (Saccharum sp.) no mundo. A produção estimada para a safra 2019/2020 é de 622,3 milhões de toneladas. A cana-de-açúcar é também a cultura mais eficiente para produção de energia renovável nas regiões tropicais e subtropicais, além da produção de etanol, o cultivo é também fonte de açúcar, biomassa, etanol de segunda geração, aguardente, insumos para ração animal e eletricidade. Os processos que sinalizam o acúmulo de sacarose e fibra em diferentes variedades de cana precisam ser melhores estudados e compreendidos. A vantagem de se produzir mais fibra em detrimento do açúcar é que as plantas serão mais rústicas, com menor exigência de solo, clima, água e nutrientes e maior resistência a pragas e doenças O acúmulo de sacarose depende de diversos processos metabólicos, dentre eles, a atividade fotossintética e a capacidade dos tecidos dreno em acumular compostos de carbono produzido pelas folhas. Dessa forma, o objetivo deste trabalho foi caracterizar e correlacionar aspectos anatômicos, morfológicos, fisiológicos e tecnológicos de três genótipos de cana-de- açúcar contrastantes para teores de sacarose e fibra. Foram observadas diferenças na expressão fenotípica entre a espécie ancestral representante de S. spontaneum e os cultivares RB855156 e SP80-3280. Não constatou-se diferença estatística entre os genótipos nas avaliações de trocas gasosas e pigmentos fotossintéticos. Por outro lado, o cultivar RB855156 se destacou apresentando a maior densidade estomática da superfície abaxial. Por meio das avaliações tecnológicas, observamos que, a espécie ancestral, S. spontaneum destaque para características relacionadas à produção de biomassa, enquanto os cultivares comerciais, oriundos de programas de melhoramento genético, carregam maiores traços para a produção de sacarose. Por meio das análises de correlação foi observado que algumas características apresentaram correlações significativas positivas e outras significativas negativas, sugerindo que o melhoramento genético atuou de forma a beneficiar características de interesse comercial, como por exemplo, Pol%cana, DC e AC (positivamente correlacionadas) e FB, FDN, FDA, DAD e DAB (negativamente correlacionadas). As correlações, se avaliadas em maior número de genótipos e com maior representatividade das espécies que compõem o complexo Saccharum, entre as características anatômicas, fisiológicas, morfológicas e tecnológicas possibilitariam uma melhor compreensão dessas correlações. Em adição, estudos com outros genótipos de cana-de-açúcar que compõem o complexo Saccharum podem contribuir para aumentar os conhecimentos sobre esses processos metabólicos sobre as diferenças durante o desenvolvimento das plantas. Brazil is the biggest producer of sugarcane (Saccharum sp.) in the world. Estimated production for the 2019/2020 crop is 622.3 million tons. Sugarcane is also the most efficient crop for renewable energy production in tropical and subtropical regions. In addition to the production of sugar, cultivation is also a source of ethanol, biomass, second generation ethanol, sugarcane liquor, inputs for animal feed and electricity. The processes that signal the accumulation of sucrose and fiber in different varieties of cane need to be better studied and understood. The advantage of producing more fiber at the expense of sugar is that the plants will be more rustic, with less soil, climate, water and nutrients requirements and greater resistance to pests and diseases. Sucrose accumulation depends on several metabolic processes, among them, photosynthetic activity and the ability of drain tissues to accumulate carbon compounds produced by leaves. Thus, the objective of this work was to characterize and correlate anatomical, morphological, physiological and technological aspects of three contrasting sugarcane genotypes for sucrose and fiber contents. Differences in phenotypic expression were observed between the ancestral species representing S. spontaneum and the cultivars RB855156 and SP80-3280. There was no statistical difference between the genotypes in the gas exchange and photosynthetic pigment evaluations. On the other hand, the cultivar RB855156 stood out with the highest stoma density on the abaxial surface. Through technological evaluations, we observed that the ancestral species, S. spontaneum was highlighted for characteristics related to the production of biomass, while commercial cultivars, coming from genetic improvement programs, carry greater traits for the production of sucrose. Through the correlation analyzes it was observed that some characteristics showed significant positive correlations and others significant negative ones, suggesting that the genetic improvement acted in a way to benefit characteristics of commercial interest, as for example, Pol% cane, DC and AC (positively correlated) and FB, NDF, FDA, DAD and DAB (negatively correlated). The correlations, if evaluated in a greater number of genotypes and with greater representativeness of the species that make up the Saccharum complex, among the anatomical, physiological, morphological and technological characteristics would allow a better understanding of these correlations. In addition, studies with other sugarcane genotypes that make up the Saccharum complex can contribute to increase the knowledge about these metabolic processes about the differences during the development of plants.

The development of biomass crops aims to meet industrial yield demands to become a profitable and sustainable activity. Achieving these goals in an energy crop such as sugarcane relies on breeding for sucrose accumulation, fiber content and tillering capacity. Sucrose storage depends on transport from leaves to culms driven by enzymes involved in sucrose synthesis and hydrolysis. High biomass genotypes often use photosynthesis products to produce lignocellulosic compounds to form the cell wall. To expand the understanding of the pathways related to these traits, we evaluated gene expression of two groups of genotypes contrasting in biomass yield, as well as testing for differences among members within the same group. First visible dewlap leaves were collected from six genotypes of each group to perform RNA-Seq. We found evidence that both groups differ with regard to genomic stress caused by polyploidy, as indicated by the enrichment of genes involved in transposition activity and defense response processes. Although carbon assimilation terms were not enriched, genes annotated with such terms were co-expressed with those coding for members of hormonal pathways. Sucrose phosphate synthase and hydrolytic enzymes coding genes were upregulated in leaves of sucrose-accumulating genotypes, as genes coding for enzymes involved in the biosynthesis of lignin. Compared to other high biomass accessions, the hybrid US85-1008 presented upregulation of photosynthesis-related genes probably due to its sink demand to store sugar in culms. This study expands the knowledge of gene expression in sugarcane leaves, revealing differences between and within phenotypically distinct groups.