Tonoplast Sugar Transporters (SbTSTs) Putatively Control Sucrose Accumulation in Sweet Sorghum Stems

Carbohydrates are differentially partitioned in sweet versus grain sorghums. While the latter preferentially accumulate starch in the grain, the former primarily store large amounts of sucrose in the stem. Previous work determined that neither sucrose metabolizing enzymes nor changes in Sucrose transporter (SUT) gene expression accounted for the carbohydrate partitioning differences. Recently, 2 additional classes of sucrose transport proteins, Tonoplast Sugar Transporters (TSTs) and SWEETs, were identified; thus, we examined whether their expression tracked sucrose accumulation in sweet sorghum stems. We determined 2 TSTs were differentially expressed in sweet vs. grain sorghum stems, likely underlying the massive difference in sucrose accumulation. A model illustrating potential roles for different classes of sugar transport proteins in sorghum sugar partitioning is discussed

Tonoplast Sugar Transporters (SbTSTs) Putatively Control Sucrose Accumulation in Sweet Sorghum Stems

Carbohydrates are differentially partitioned in sweet versus grain sorghums. While the latter preferentially accumulate starch in the grain, the former primarily store large amounts of sucrose in the stem. Previous work determined that neither sucrose metabolizing enzymes nor changes in Sucrose transporter (SUT) gene expression accounted for the carbohydrate partitioning differences. Recently, 2 additional classes of sucrose transport proteins, Tonoplast Sugar Transporters (TSTs) and SWEETs, were identified; thus, we examined whether their expression tracked sucrose accumulation in sweet sorghum stems. We determined 2 TSTs were differentially expressed in sweet vs. grain sorghum stems, likely underlying the massive difference in sucrose accumulation. A model illustrating potential roles for different classes of sugar transport proteins in sorghum sugar partitioning is discussed

Suboptimal light conditions influence source-sink metabolism during flowering

Reliance on carbohydrates during flower forcing was investigated in one early and one late flowering cultivar of azalea (Rhododendron simsii hybrids). Carbohydrate accumulation, invertase activity, and expression of a purported sucrose synthase gene (RsSUS) was monitored during flower forcing under suboptimal (natural) and optimal (supplemental light) light conditions, after a cold treatment (7 degrees C + dark) to break flower bud dormancy. Post-production sucrose metabolism and flowering quality was also assessed. Glucose and fructose concentrations and invertase activity increased in petals during flowering, while sucrose decreased. In suboptimal light conditions RsSUS expression in leaves increased as compared to optimal light conditions, indicating that plants in suboptimal light conditions have a strong demand for carbohydrates. However, carbohydrates in leaves were markedly lower in suboptimal light conditions compared to optimal light conditions. This resulted in poor flowering of plants in suboptimal light conditions. Post production flowering relied on the stored leaf carbon, which could be accumulated under optimal light conditions in the greenhouse. These results show that flower opening in azalea relies on carbohydrates imported from leaves and is source-limiting under suboptimal light conditions

Enhancing soybean photosynthetic CO2 assimilation using a cyanobacterial membrane protein, ictB

Abstract Soybean C3 photosynthesis can suffer a severe loss in efficiency due to photorespiration and the lack of a carbon concentrating mechanism (CCM) such as those present in other plant species or cyanobacteria. Transgenic soybean (Glycine max cv. Thorne) plants constitutively expressing cyanobacterial ictB (inorganic carbon transporter B) gene were generated using Agrobacterium-mediated transformation. Although more recent data suggest that ictB does not actively transport HCO3-/CO2, there is nevertheless mounting evidence that transformation with this gene can increase higher plant photosynthesis. The hypothesis that expression of the ictB gene would improve photosynthesis, biomass production and seed yield in soybean was tested, in two independent replicated greenhouse and field trials. Results showed significant increases in photosynthetic CO2 uptake (Anet) and dry mass in transgenic relative to wild type (WT) control plants in both the greenhouse and field trials. Transgenic plants also showed increased photosynthetic rates and biomass production during a drought mimic study. The findings presented herein demonstrate that ictB, as a single-gene, contributes to enhancement in various yield parameters in a major commodity crop and point to the significant role that biotechnological approaches to increasing photosynthetic efficiency can play in helping to meet increased global demands for food

Crop improvement through biotechnology: Targeting drought resistance and photosynthesis

The world population is projected to grow from the current 7 to about 9 billion by 2050. One of the major challenges that will face agriculture in the next few decades is sustainable food production under climate uncertainties and dwindling natural resources to meet the increased global needs for food. Plant biotechnology plays a vital role in meeting this global challenge. The goal of this research was to investigate the use of biotechnology to improve plant photosynthesis, water use efficiency and drought resistance, to either increase yield and/or alleviate the impacts of water stress on biomass and yield. In the first assay, the use of two Arabidopsis thaliana promoters, RD29A and RD29B, in soybean (Glycine max (L.) Merr.) was investigated and results suggest that they may be useful in controlling transgenes targeted to enhance drought resistance in soybean as long as there are no agronomic penalties associated with low-level expression in the absence of stress. In the second assay, the expression of AQPV1, an aquaporin gene from Chlorella virus MT325, and its effect in mitigating drought stress in tobacco (Nicotiana tabacum) was investigated. Results showed that the transformed AQPV1 plants maintained higher photosynthetic rates, less negative water and osmotic potentials, and accumulated greater biomass when subjected to drought compared to control plants. In the third assay, the potential use of C4 enzymes from Cyanobacteria to improve C3 photosynthesis was investigated. The cyanobacterial ictB (inorganic carbon transporter B) and FBP/SBPase (fructose-1,6-/sedoheptulose-1,7-biphosphatase) genes were placed under control of constitutive promoters and introduced into soybean chloroplasts via Agrobacterium-mediated transformation. The former gene is involved in HCO3− accumulation and the latter catalyzes the hydrolysis of both fructose-1,6-bisphosphate and sedoheptulose-1,7-bisphosphate in the Calvin cycle. Leaf physiological data collected in both the greenhouse and the field revealed that transgenic soybeans displayed higher leaf photosynthetic rates compared to control plants. In addition, some of the tested transgenic events performed better than control plants when exposed to soil dry-down experiments. Results from these assays contribute to the ongoing research aiming at using plant genetic manipulations to increase crop productivity and alleviate environmental stresses

Photosynthetic performance of invasive \u3ci\u3ePinus ponderosa\u3c/i\u3e and \u3ci\u3eJuniperus virginiana\u3c/i\u3e seedlings under gradual soil water depletion

Changes in climate, land management and fire regime have contributed to woody species expansion into grasslands and savannas worldwide. In the USA, Pinus ponderosa P. & C. Lawson and Juniperus virginiana L. are expanding into semiarid grasslands of Nebraska and other regions of the Great Plains. We examined P. ponderosa and J. virginiana seedling response to soil water content, one of the most important limiting factors in semiarid grasslands, to provide insight into their success in the region. Photosynthesis, stomatal conductance, maximum photochemical efficiency of PSII, maximum carboxylation velocity, maximum rate of electron transport, stomatal limitation to photosynthesis, water potential, root-to-shoot ratio, and needle nitrogen content were followed under gradual soil water depletion for 40 days. J. virginiana maintained lower Ls, higher A, gs, and initial Fv/Fm, and displayed a more gradual decline in Vcmax and Jmax with increasing water deficit compared to P. ponderosa. J. virginiana also invested more in roots relative to shoots compared to P. ponderosa. Fv/Fm showed high PSII resistance to dehydration in both species. Photoinhibition was observed at ~30% of field capacity. Soil water content was a better predictor of A and gs than Ψ, indicating that there are other growth factors controlling physiological processes under increased water stress. The two species followed different strategies to succeed in semiarid grasslands. P. ponderosa seedlings behaved like a drought-avoidant species with strong stomatal control, while J. virginiana was more of a drought-tolerant species, maintaining physiological activity at lower soil water content. Differences between the studied species and the ecological implications are discussed