Its large genome and high polyploidy makes sugarcane (Saccharum spp.) a singularly challenging crop to study and improve using genetic approaches. To provide large numbers of functionally characterized candidate genes that might be tested for direct association (rather than distant linkage) with economically important traits, we sequenced the 5' ends of 9,216 clones from three cDNA libraries (apex, leaf and mature internode), representing 3,401 non-redundant sequences. About 57% of these sequences could be assigned a tentative function based on statistically significant similarity to previously characterized proteins or DNA sequences. Another 28% corresponded to previously identified, but uncharacterized, sequences. Some of the remaining unidentified sequences were predicted to be genes which could potentially be new to plants or unique to sugarcane. Comparisons of the sugarcane ESTs to a large sorghum EST database revealed similar compositions of expressed genes between some different tissues. Comparison to a detailed Arabidopsis protein database showed some highly conserved sequences, which might be useful DNA markers for pan-angiosperm comparative mapping. These EST sequences provide a foundation for many new studies to accelerate isolation of agronomically important genes from the cumbersome sugarcane genome.

Visual Abstract

A novel layered compound, NaCuSb, has been successfully synthesized from elements. This unique structure crystallizes in the hexagonal space group P6/mmc and has lattice constants of a = 4.2166(2) Å and c = 24.041(1) Å. The structure consists of complex Cu/Sb 2D blocks separated by Na ions. These blocks contain graphene-like hexagonal layers of either Cu or CuSb. The solid-state transformations in the Na-Cu-Sb system between CuSb-NaCuSb-NaCuSb were explored using annealing at different partial vapor pressures of Na, differential scanning calorimetry, and in situ synchrotron powder X-ray diffraction. Full reversibility of the transformation was observed, indicating that the bulk 3D CuSb phase is capable of reversible intercalation of Na ions, forming layered intercalated phases similar to intercalated graphite. The characterization of the transport properties shows that the metallic nature of the electrical conductivity is preserved, even for the Na-rich phase of NaCuSb. Electronic structure calculations support metallic properties in the Cu-Sb layers and predict that no bands cross the Fermi level across the layers, supporting NaCuSb as a two-dimensional metal.