Are sucrose transporter expression profiles linked with patterns of biomass partitioning in Sorghum phenotypes?

Sorghum bicolor is a genetically diverse C4 monocotyledonous species, encompassing varieties capable of producing high grain yields as well as sweet types which accumulate soluble sugars (predominantly sucrose) within their stems to high concentrations. Sucrose produced in leaves (sources) enters the phloem and is transported to regions of growth and storage (sinks). It is likely that sucrose transporter (SUT) proteins play pivotal roles in phloem loading and the delivery of sucrose to growth and storage sinks in all Sorghum ecotypes. Six SUTs are present in the published Sorghum genome, based on the BTx623 grain cultivar. Homologues of these SUTs were cloned and sequenced from the sweet cultivar Rio, and compared with the publically available genome information. SbSUT5 possessed nine amino acid sequence differences between the two varieties. Two of the remaining five SUTs exhibited single variations in their amino acid sequences (SbSUT1 and SbSUT2) whilst the rest shared identical sequences. Complementation of a mutant Saccharomyces yeast strain (SEY6210), unable to grow up on sucrose as the sole carbon source, demonstrated that the Sorghum SUTs were capable of transporting sucrose. SbSUT1, SbSUT4, and SbSUT6 were highly expressed in mature leaf tissues and hence may contribute to phloem loading. In contrast, SbSUT2 and SbSUT5 were expressed most strongly in sinks consistent with a possible role of facilitating sucrose import into stem storage pools and developing inflorescences.Ricky J. Milne, Caitlin S. Byrt, John W. Patrick and Christopher P. L. Gro

Cell Wall Development in an Elongating Internode of Setaria

Although Setaria has been proposed as a model to investigate C4 photosynthesis, it may also be considered a suitable representative for biofuel feedstock species that are predominantly closely related panicoid grasses. In order to extend our understanding of the fundamental molecular and physiological mechanisms underpinning cell wall deposition as they occur during plant development, we have investigated an elongating stem internode of S. viridis. The chosen internode progressed from an active meristem and region of cell expansion at the base of the internode towards maturing fully expanded cells at the top of the internode. Along this developmental gradient, RNAseq of the mRNA fraction of the transcriptome was undertaken. A holistic understanding of the synthesis, composition and structure of the cell wall and the molecular mechanisms that signal the transition from primary to secondary cell wall synthesis will be integral to engineering crops with a structure that lends itself to more efficient deconstruction

Energy sorghum hybrids: functional dynamics of high nitrogen use efficiency

The nitrogen use efficiency (NUE) of high biomass energy sorghum hybrid plants increased during 180 days of growth to a maximum of 370g DWgN. Shoot N uptake was biphasic and continued for 120 days. Leaf N accumulation was rapid until day 60. Specific leaf nitrogen (SLN) varied from 0.9 to 1.7gNm green leaf area, a typical range for C4 grass canopies. Stem N increased to a maximum at day 120. NUE increased during development in parallel with increasing stem to leaf biomass ratio and as stems decreased from 0.7% to 0.2% N. At the end of the season, green leaves were ~1% N, represented 17% of total shoot biomass and accounted for 50% of N present in shoots (above ground biomass) while stems were ~0.2% N, comprised 83% of shoot biomass and accounted for 50% of shoot N. High NUE was due in part to N-remobilization from lower leaves and stem nodes/internodes to upper portions of the canopy. Up to 70% of dry weight and 90% of N was remobilized during senescence of lower leaves and 70% of N was remobilized from lower stem nodes/internodes. The NUE of energy sorghum was similar to Saccharum officinarum and Miscanthus x giganteus, and higher than grain Sorghum bicolor, Zea mays, and Panicum virgatum. High NUE of energy S. bicolor is due to long duration of vegetative growth, high stem to leaf biomass ratio, and very efficient N-remobilization from lower leaves and stem internodes during development