Contribution of fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase to the photosynthetic rate and carbon flow in the Calvin cycle in transgenic plants

TaNF-YC11, one of the light-upregulated NF-YC members in Triticum aestivum, is co-regulated with photosynthesis-related genes

Nuclear factor Y (NF-Y) is a heterotrimeric transcription factor complex. Each of the NF-Y subunits (NF-YA, NF-YB and NF-YC) in plants is encoded by multiple genes. Quantitative RT-PCR analysis revealed that five wheat NF-YC members (TaNF-YC5, 8, 9, 11 and 12) were upregulated by light in both the leaf and seedling shoot. Co-expression analysis of Affymetrix wheat genome array datasets revealed that transcript levels of a large number of genes were consistently correlated with those of the TaNF-YC11 and TaNF-YC8 genes in three to four separate Affymetrix array datasets. TaNF-YC11-correlated transcripts were significantly enriched with the Gene Ontology term photosynthesis. Sequence analysis in the promoters of TaNF-YC11-correlated genes revealed the presence of putative NF-Y complex binding sites (CCAAT motifs). Quantitative RT-PCR analysis of a subset of potential TaNF-YC11 target genes showed that ten out of the 13 genes were also light-upregulated in both the leaf and seedling shoot and had significantly correlated expression profiles with TaNF-YC11. The potential target genes for TaNF-YC11 include subunit members from all four thylakoid membrane-bound complexes required for the conversion of solar energy into chemical energy and rate-limiting enzymes in the Calvin cycle. These data indicate that TaNF-YC11 is potentially involved in regulation of photosynthesis-related genes.

Changes in the gene expression profile of Arabidopsis thaliana after infection with Tobacco etch virus

BACKGROUND

Tobacco etch potyvirus (TEV) has been extensively used as model system for the study of positive-sense RNA virus infecting plants. TEV ability to infect Arabidopsis thaliana varies among ecotypes. In this study, changes in gene expression of A. thaliana ecotype Ler infected with TEV have been explored using long-oligonucleotide arrays. A. thaliana Ler is a susceptible host that allows systemic movement, although the viral load is low and syndrome induced ranges from asymptomatic to mild. Gene expression profiles were monitored in whole plants 21 days post-inoculation (dpi). Microarrays contained 26,173 protein-coding genes and 87 miRNAs.

RESULTS

Expression analysis identified 1727 genes that displayed significant and consistent changes in expression levels either up or down, in infected plants. Identified TEV-responsive genes encode a diverse array of functional categories that include responses to biotic (such as the systemic acquired resistance pathway and hypersensitive responses) and abiotic stresses (droughtness, salinity, temperature, and wounding). The expression of many different transcription factors was also significantly affected, including members of the R2R3-MYB family and ABA-inducible TFs. In concordance with several other plant and animal viruses, the expression of heat-shock proteins (HSP) was also increased. Finally, we have associated functional GO categories with KEGG biochemical pathways, and found that many of the altered biological functions are controlled by changes in basal metabolism.

CONCLUSION

TEV infection significantly impacts a wide array of cellular processes, in particular, stress-response pathways, including the systemic acquired resistance and hypersensitive responses. However, many of the observed alterations may represent a global response to viral infection rather than being specific of TEV.

Molecular design of photosynthesis-elevated chloroplasts for mass accumulation of a foreign protein

In order to increase production of a useful protein by the chloroplast transformation technique, it seems to be necessary to determine the upper limit for the accumulation of a biologically active foreign protein in chloroplasts and then improve photosynthetic capacity and plant productivity. Here we show that the stromal fractions of tobacco chloroplasts could accommodate an additional 200-260 mg ml(-1) of green fluorescent protein in the stroma without any inhibition of gas exchange under various light intensity and growth conditions. The minimum amount of fructose-1,6-/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) limiting photosynthesis was then calculated. Analyses of the photosynthetic parameters and the metabolites of transformants into which FBP/SBPase was introduced with various types of promoter (PpsbA, Prrn, Prps2 and Prps12) indicated that a 2- to 3-fold increase in levels of FBPase and SBPase activity is sufficient to increase the final amount of dry matter by up to 1.8-fold relative to the wild-type plants. Their increases were equivalent to an increase of <1 mg ml(-1) of the FBP/SBPase protein in chloroplasts and were calculated to represent <1% of the protein accumulated via chloroplast transformation. Consequently, >99% of the additional 200-260 mg ml(-1) of protein expressed in the chloroplasts could be used for the production of useful proteins in the photosynthesis-elevated transplastomic plants having FBP/SBPase.

Role of the methionine sulfoxide reductase MsrB3 in cold acclimation in Arabidopsis

Methionine residues of proteins are a major target for oxidation by reactive oxygen species (ROS), which are generated in response to a variety of stress conditions. Methionine sulfoxide (MetO) reductases are present in most organisms and play protective roles in the cellular response to oxidative stress, reducing oxidized MetO back to Met. Previously, an Arabidopsis MetO reductase, MsrB3, was identified as a cold-responsive protein. Here we report that MsrB3 functions in the process of cold acclimation, thus contributing to cold tolerance. In contrast to normal, wild-type plants, msrb3 mutant plants lost the ability to become tolerant to freezing temperatures following cold pre-treatment. Furthermore, when exposed to low temperature, msrb3 plants exhibited a larger increase in MetO and H(2)O(2) content and electrolyte leakage compared with wild-type and MsrB3 transgenic plants. It is also shown that MsrB3 is localized at the endoplasmic reticulum (ER). We propose that MsrB3 plays an important role in cold tolerance by eliminating MetO and ROS that accumulate at the ER during cold acclimation.

Optimizing the distribution of resources between enzymes of carbon metabolism can dramatically increase photosynthetic rate: a numerical simulation using an evolutionary algorithm

The distribution of resources between enzymes of photosynthetic carbon metabolism might be assumed to have been optimized by natural selection. However, natural selection for survival and fecundity does not necessarily select for maximal photosynthetic productivity. Further, the concentration of a key substrate, atmospheric CO(2), has changed more over the past 100 years than the past 25 million years, with the likelihood that natural selection has had inadequate time to reoptimize resource partitioning for this change. Could photosynthetic rate be increased by altered partitioning of resources among the enzymes of carbon metabolism? This question is addressed using an "evolutionary" algorithm to progressively search for multiple alterations in partitioning that increase photosynthetic rate. To do this, we extended existing metabolic models of C(3) photosynthesis by including the photorespiratory pathway (PCOP) and metabolism to starch and sucrose to develop a complete dynamic model of photosynthetic carbon metabolism. The model consists of linked differential equations, each representing the change of concentration of one metabolite. Initial concentrations of metabolites and maximal activities of enzymes were extracted from the literature. The dynamics of CO(2) fixation and metabolite concentrations were realistically simulated by numerical integration, such that the model could mimic well-established physiological phenomena. For example, a realistic steady-state rate of CO(2) uptake was attained and then reattained after perturbing O(2) concentration. Using an evolutionary algorithm, partitioning of a fixed total amount of protein-nitrogen between enzymes was allowed to vary. The individual with the higher light-saturated photosynthetic rate was selected and used to seed the next generation. After 1,500 generations, photosynthesis was increased substantially. This suggests that the "typical" partitioning in C(3) leaves might be suboptimal for maximizing the light-saturated rate of photosynthesis. An overinvestment in PCOP enzymes and underinvestment in Rubisco, sedoheptulose-1,7-bisphosphatase, and fructose-1,6-bisphosphate aldolase were indicated. Increase in sink capacity, such as increase in ADP-glucose pyrophosphorylase, was also indicated to lead to increased CO(2) uptake rate. These results suggest that manipulation of partitioning could greatly increase carbon gain without any increase in the total protein-nitrogen investment in the apparatus for photosynthetic carbon metabolism.

Genetic engineering approaches to improve bioethanol production from maize

Biofuels such as bioethanol are becoming a viable alternative to fossil fuels. Utilizing agricultural biomass for the production of biofuel has drawn much interest in many science and engineering disciplines. As one of the major crops, maize offers promise in this regard. Compared to other crops with biofuel potential, maize can provide both starch (seed) and cellulosic (stover) material for bioethanol production. However, the combination of food, feed and fuel in one crop, although appealing, raises concerns related to the land delineation and distribution of maize grown for energy versus food and feed. To avoid this dilemma, the conversion of maize biomass into bioethanol must be improved. Conventional breeding, molecular marker assisted breeding and genetic engineering have already had, and will continue to have, important roles in maize improvement. The rapidly expanding information from genomics and genetics combined with improved genetic engineering technologies offer a wide range of possibilities for enhanced bioethanol production from maize.