Abstract
Background -Sucrose content is a highly desirable trait in sugarcane as the worldwide demand for cost-effective biofuels surges. Sugarcane cultivars differ in their capacity to accumulate sucrose and breeding programs routinely perform crosses to identify genotypes able to produce more sucrose. Sucrose content in the mature internodes reach around 20% of the culms dry weight. Genotypes in the populations reflect their genetic program and may display contrasting growth, development, and physiology, all of which affect carbohydrate metabolism. Few studies have profiled gene expression related to sugarcane's sugar content. The identification of signal transduction components and transcription factors that might regulate sugar accumulation is highly desirable if we are to improve this characteristic of sugarcane plants.Results -We have evaluated thirty genotypes that have different Brix (sugar) levels and identified genes differentially expressed in internodes using cDNA microarrays. These genes were compared to existing gene expression data for sugarcane plants subjected to diverse stress and hormone treatments. The comparisons revealed a strong overlap between the drought and sucrose-content datasets and a limited overlap with ABA signaling. Genes associated with sucrose content were extensively validated by qRT-PCR, which highlighted several protein kinases and transcription factors that are likely to be regulators of sucrose accumulation. The data also indicate that aquaporins, as well as lignin biosynthesis and cell wall metabolism genes, are strongly related to sucrose accumulation. Moreover, sucrose-associated genes were shown to be directly responsive to short term sucrose stimuli, confirming their role in sugar-related pathways.Conclusion -Gene expression analysis of sugarcane populations contrasting for sucrose content indicated a possible overlap with drought and cell wall metabolism processes and suggested signaling and transcriptional regulators to be used as molecular markers in breeding programs. Transgenic research is necessary to further clarify the role of the genes and define targets useful for sugarcane improvement programs based on transgenic plants.
Highlights
The importance of bioenergy-generating crops such as sugarcane is increasing rapidly and is likely to play an increasing role given the environmental and economical challenges of fossil fuel usage
In this report we present the results of a large-scale analysis of the transcriptome of thirty genotypes grown in the field. cDNA microarrays were used to compare high- and low-Brix individuals and a comparison was made to reveal gene expression patterns that correlate with sucrose content, culm development, sugar treatments, drought and ABA treatment
Results cDNA microarrays were used to identify genes that were differentially expressed in genotypes contrasting for sucrose content
Summary
The importance of bioenergy-generating crops such as sugarcane is increasing rapidly and is likely to play an increasing role given the environmental and economical challenges of fossil fuel usage. Sugarcane belongs to the Saccharum L. genus, which derives from crosses of the domesticated species S. officinarum (a group that has sweet canes with thick and juicy culms), natural hybrids (S. sinense and S. barberi) and S. spontaneum (a wild species with no sugar and thin culms). All modern cultivars are derived from a few intercrossings of these hybrids [1,2,3,4,5]. Sucrose content is a phenotypic characteristic selected over centuries by breeding programs. Breeding programs routinely perform crosses to identify genotypes able to produce more sucrose early in the crop season to allow for continuous sugar production throughout the year. Sucrose content in the mature internodes can reach around 20% of the culms dry weight while lower sucrose levels are observed in younger internodes where glucose and fructose are predominant
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