BackgroundSugarcane (Saccharum spp.) is the main raw material for sugar and ethanol production. Among the abiotic stress, drought is the main one that negatively impact sugarcane yield. Although gene expression analysis through quantitative PCR (qPCR) has increased our knowledge about biological processes related to drought, gene network that mediates sugarcane responses to water deficit remains elusive. In such scenario, validation of reference gene is a major requirement for successful analyzes involving qPCR. ResultsIn this study, candidate genes were tested for their suitable as reference genes for qPCR analyses in two sugarcane cultivars with varying drought tolerance. Eight candidate reference genes were evaluated in leaves sampled in plants subjected to water deficit in both field and greenhouse conditions. In addition, five genes were evaluated in shoot roots of plants subjected to water deficit by adding PEG8000 to the nutrient solution. NormFinder and RefFinder algorithms were used to identify the most stable gene(s) among genotypes and under different experimental conditions. Both algorithms revealed that in leaf samples, UBQ1 and GAPDH genes were more suitable as reference genes, whereas GAPDH was the best reference one in shoot roots.ConclusionReference genes suitable for sugarcane under water deficit were identified, which would lead to a more accurate and reliable analysis of qPCR. Thus, results obtained in this study may guide future research on gene expression in sugarcane under varying water conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-017-0178-2) contains supplementary material, which is available to authorized users.

Drought is the most significant environmental stress for agricultural production worldwide, and tremendous efforts have been made to improve crop yield under the increasing water scarcity. Transcription factors are major players in the regulation of water stress-related genes in plants. Recently, different MYB transcription factors were characterized for their involvement in drought response. A sugarcane R2R3-MYB gene (ScMYBAS1) and its four alternative forms of transcript (ScMYAS1-2, ScMYBAS1-3, ScMYBAS1-4 and ScMYBAS1-5) were identified in this study. The subcellular localization, in Nicotiniana benthamiana, of the TFs fused in frame with GFP revealed that ScMYBAS1-2-GFP and ScMYBAS1-3-GFP were observed in the nucleus. The overexpression of ScMYBAS1-2 and ScMYBAS1-3 spliced transcripts in rice promoted change in plant growth under both well-watered and drought conditions. The ScMYBAS1-2 and ScMYBAS1-3 transgenic lines revealed a higher relative water content (RWC) compared to the wild type before maximum stress under drought conditions. The ScMYBAS1-2 transgenic lines showed a reduction in biomass (total dry weight). Conversely, ScMYBAS1-3 showed an increased biomass (total dry weight) relative to the wild-type. The overexpression of ScMYBAS1-3 in rice transgenic lines showed involvement with drought tolerance and biomass and, for this reason, was considered a good target for plant transformation, particularly for use in developing genotypes with drought tolerance and biomass accumulation.

A sugarcane gene encoding a dirigent-jacalin , ShDJ , was induced under drought stress. To elucidate its biological function, we integrated a ShDJ -overexpression construction into the rice Nipponbare genome via Agrobacterium -mediated transformation. Two transgenic lines with a single copy gene in T 0 were selected and evaluated in both the T 1 and T 4 generations. Transgenic lines had drastically improved survival rate under water deficit conditions, at rates close to 100%, while WT did not survive. Besides, transgenic lines had improved biomass production and higher tillering under water deficit conditions compared with WT plants. Reduced pectin and hemicellulose contents were observed in transgenic lines compared with wild-type plants under both well-watered and water deficit conditions, whereas cellulose content was unchanged in line #17 and reduced in line #29 under conditions of low water availability. Changes in lignin content under water deficit were only observed in line #17. However, improvements in saccharification were found in both transgenic lines along with changes in the expression of OsNTS1/2 and OsMYB58/63 secondary cell wall biosynthesis genes. ShDJ -overexpression up-regulated the expression of the OsbZIP23 , OsGRAS23 , OsP5CS , and OsLea3 genes in rice stems under well-watered conditions. Taken together, our data suggest that ShDJ has the potential for improving drought tolerance, plant biomass accumulation, and saccharification efficiency.

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gratidão pelo eterno aprendizado, dedicação, confiança e paciência, que muito colaboraram para minha formação acadêmica e pessoal, e também pelo exemplo de determinação e ação em prol da ciência.-Aos amigos e co-orientadores acadêmicos Dra. Paula Macedo Nobile e Dr. Michael dos Santos Brito pelos ensinamentos, discussões, companheirismo e dedicação plena no desenvolvimento e conclusão deste projeto.-À Profa. Dra. Maria Helena de Souza Goldman pela oportunidade e confiança concedidas durante meu ingresso na vida acadêmica, e pelas constantes demonstrações de altruísmo e suporte intelectual.-Ao Laboratório de Fisiologia Molecular de Plantas da Unicamp (LaFiMP), sob a figura do Prof. Dr. Paulo Mazzafera, pela contínua colaboração e suporte experimental durante o desenvolvimento deste projeto. Em especial à Juliana Mayer, Juan Pablo Mortillha e Eduardo Kiyota pela dedicação e auxílio na condução dos experimentos.-Aos meus pais Carlos Boer Martins e Letícia Maria Palma Boer Martins, pelas contínuas demonstrações de apoio, carinho, amor, respeito e confiança, durante todas as fases da minha vida.-Á Juliana Maria de Lima pelas constantes demonstrações de amor e afeto, pelo sorriso sempre aberto, pelo companherismo incondicional, pelas discussões científicas e humanas, e por optar partilhar sua vida a dois, afinal a felicidade só existe quando compartilhada.