Sucrose accumulation and enzyme activities in callus culture of sugarcane

The activities of sucrose phosphate synthase (SPS), sucrose synthase (SUSY), neutral invertase (NI) and soluble acid invertase (SAI) were measured in callus cultures of four Mexican sugarcane cultivars (Saccharum spp.) with a different capacity to accumulate sucrose in stem parenchyma cells. The results indicated that sucrose accumulation in callus was positively correlated to the activity of SPS and SUSY and negatively to the activity of SAI and NI while SPS explained most of the variation found for sucrose accumulation and NI least.The research was funded by the department of Biotechnology and Bioengineering CINVESTAV Mexico City, and F. G.-M. received grant-aided support from CONACyT, Mexico.     

Expansins: roles in plant growth and potential applications in crop improvement

Key message

Results from various expansin related studies have demonstrated that expansins present an opportunity to improve various crops in many different aspects ranging from yield and fruit ripening to improved stress tolerance.

Abstract

The recent advances in expansin studies were reviewed. Besides producing the strength that is needed by the plants, cell walls define cell shape, cell size and cell function. Expansins are cell wall proteins which consist of four sub families; α-expansin, β-expansin, expansin-like A and expansin-like B. These proteins mediate cell wall loosening and they are present in all plants and in some microbial organisms and other organisms like snails. Decades after their initial discovery in cucumber, it is now clear that these small proteins have diverse biological roles in plants. Through their ability to enable the local sliding of wall polymers by reducing adhesion between adjacent wall polysaccharides and the part they play in cell wall remodeling after cytokinesis, it is now clear that expansins are required in almost all plant physiological development aspects from germination to fruiting. This is shown by the various reports from different studies using various molecular biology approaches such as gene achieve these many roles through their non-enzymatic wall loosening ability. This paper reviews and summarizes some of the reported functions of expansins and outlines the potential uses of expansins in crop improvement programs.

     

Applications and potential of genome editing in crop improvement

Genome-editing tools provide advanced biotechnological techniques that enable the precise and efficient targeted modification of an organism’s genome. Genome-editing systems have been utilized in a wide variety of plant species to characterize gene functions and improve agricultural traits. We describe the current applications of genome editing in plants, focusing on its potential for crop improvement in terms of adaptation, resilience, and end-use. In addition, we review novel breakthroughs that are extending the potential of genome-edited crops and the possibilities of their commercialization. Future prospects for integrating this revolutionary technology with conventional and new-age crop breeding strategies are also discussed.     

Sucrose partitioning between vascular bundles and storage parenchyma in the sugarcane stem: a potential role for the ShSUT1 sucrose transporter

A transporter with homology to the SUT/SUC family of plant sucrose transporters was isolated from a sugarcane (Saccharum hybrid) stem cDNA library. The gene, designated ShSUT1, encodes a protein of 517 amino acids, including 12 predicted membrane-spanning domains and a large central cytoplasmic loop. ShSUT1 was demonstrated to be a functional sucrose transporter by expression in yeast. The estimated K_m for sucrose of the ShSUT1 transporter was 2 mM at pH 5.5. ShSUT1 was expressed predominantly in mature leaves of sugarcane that were exporting sucrose and in stem internodes that were actively accumulating sucrose. Immunolocalization with a ShSUT1-specific antiserum identified the protein in cells at the periphery of the vascular bundles in the stem. These cells became lignified and suberized as stem development proceeded, forming a barrier to apoplasmic solute movement. However, the movement of the tracer dye, carboxyfluorescein from phloem to storage parenchyma cells suggested that symplasmic connections are present. ShSUT1 may have a role in partitioning of sucrose between the vascular tissue and sites of storage in the parenchyma cells of sugarcane stem internodes.     

Apomixis for crop improvement

Summary Apomixis is a genetically controlled reproductive process by which embryos and seeds develop in the ovule without female meiosis and egg cell fertilization. Apomixis produces seed progeny that are exact replicas of the mother plant. The major advantage of apomixis over sexual reproduction is the possibility to select individuals with desirable gene combinations and to propagate them as clones. In contrast to clonal propagation through somatic embryogenesis or in vitro shoot multiplication, apomixis avoids the need for costly processes, such as the production of artificial seeds and tissue culture. It simplifies the processes of commercial hybrid and cultivar production and enables a large-scale seed production economically in both seed- and vegetatively propagated crops. In vegetatively reproduced plants (e.g., potato), the main applications of apomixis are the avoidance of phytosanitary threats and the spanning of unfavorable seasons. Because of its potential for crop improvement and global agricultural production, apomixis is now receiving increasing attention from both scientific and industrial sectors. Harnessing apomixis is a major goal in applied plant genetic engineering. In this regard, efforts are focused on genetic and breeding strategies in various plant species, combined with molecular methods to analyze apomictic and sexual modes of reproduction and to identify key regulatory genes and mechanisms underlying these processes. Also, investigations on the components of apomixis, i.e., apomeiosis, parthenogenesis, and endosperm development without fertilization, genetic screens for apomictic mutants and transgenic approaches to modify sexual reproduction by using various regulatory genes are receiving a major effort. These can open new avenues for the transfer of the apomixis trait to important crop species and will have far-reaching potentials in crop improvement regarding agricultural production and the quality of the products.     

Bt-maize as a potential trap crop for management of Eldana saccharina Walker (Lep., Pyralidae) in sugarcane

Abstract:  Notwithstanding the introduction of several pest management tactics, the stalk borer Eldana saccharina Walker (Lep., Pyralidae) remains the most serious pest in South African sugarcane. A novel tactic for managing this pest in sugarcane would be the use of a dead-end trap crop that attracts moths for oviposition and curtails subsequent larval development, thereby reducing pest population size. Glasshouse bioassays, in which moths chose to oviposit on maize producing Bacillus thuringiensis Cry1Ab toxin ( Bt -maize), non- Bt -maize or sugarcane of two cultivars (borer-resistant and -susceptible), showed that E. saccharina laid significantly more eggs and egg batches per dry leaf and unit mass of dry leaf on maize ( Bt or non- Bt ) than on either of the cane cultivars. When moths had a choice of ovipositing on 2-, 3-, 4- or 5-month-old maize ( Bt and non- Bt ), dry leaf number and mass of dry leaf material was significantly correlated with number of eggs and egg batches, indicating that older plants, which carried larger amounts of dry leaf matter, were more attractive for oviposition. Finally, glasshouse assays in which hatching larvae fed on 2.5-, 3.5- and 4.5-month-old Bt and non- Bt -maize plants, showed that the Cry1Ab toxin was effective in killing E. saccharina larvae in all Bt -maize plant growth stages, confirming that Bt -maize fulfilled the third requirement (curtailing larval development) of a dead-end trap crop for this pest. We argue that Bt -maize warrants further testing in the field as a trap crop, both alone and as a component of a 'push–pull' or habitat management system for E. saccharina in sugarcane.     

Genomics-assisted breeding for crop improvement

Genomics research is generating new tools, such as functional molecular markers and informatics, as well as new knowledge about statistics and inheritance phenomena that could increase the efficiency and precision of crop improvement. In particular, the elucidation of the fundamental mechanisms of heterosis and epigenetics, and their manipulation, has great potential. Eventually, knowledge of the relative values of alleles at all loci segregating in a population could allow the breeder to design a genotype in silico and to practice whole genome selection. High costs currently limit the implementation of genomics-assisted crop improvement, particularly for inbreeding and/or minor crops. Nevertheless, marker-assisted breeding and selection will gradually evolve into 'genomics-assisted breeding' for crop improvement.     

Plant biotechnology for crop improvement

The typical crop improvement cycle takes 10–15 years to complete and includes germplasm manipulations, genotype selection and stabilization, variety testing, variety increase, proprietary protection and crop production stages. Plant tissue culture and genetic engineering procedures that form the basis of plant biotechnology can contribute to most of these crop improvement stages. This review provides an overview of the opportunities presented by the integration of plant biotechnology into plant improvement efforts and raises some of the societal issues that need to be considered in their application.     

Combating stress with flavodoxin: a promising route for crop improvement

Environmental stresses and iron limitation are the primary causes of crop losses worldwide. Engineering strategies aimed at gaining stress tolerance have focused on overexpression of endogenous genes belonging to molecular networks for stress perception or responses. Based on the typical response of photosynthetic microorganisms to stress, an alternative approach has been recently applied with considerable success. Ferredoxin, a stress-sensitive target, was replaced in tobacco chloroplasts by an isofunctional protein, a cyanobacterial flavodoxin, which is absent in plants. Resulting transgenic lines showed wide-range tolerance to drought, chilling, oxidants, heat and iron starvation. The survival of plants under such adverse conditions would be an enormous agricultural advantage and makes this novel strategy a potentially powerful biotechnological tool for the generation of multiple-tolerant crops in the near future.     

Glycolysis in cancer: a potential target for therapy

Clinical imaging of primary and metastatic cancers with Fluoro deoxy-d-Glucose Positron Emission Tomography (FdG PET) has clearly demonstrated that increased glucose flux compared to normal tissue is a common trait of human malignancies (Gambhir, 2002) This is a consequence of a shift of glucose metabolism to less efficient glycolytic pathways in response to regional hypoxia and evolution of aerobic glycolysis in many cancer phenotypes. This distinctive metabolic profile presents an inviting target for cancer treatment and prevention. Here, we summarize the therapeutic strategies under investigation to exploit or interrupt tumor glycolytic metabolism. Although a number of approaches are under investigation, none has been sufficiently successful to warrant widespread clinical application. We point out that the environmental heterogeneity and evolutionary capacity of tumor cells that likely led to development of upregulated glycolysis could also promote adaptive strategies that confer resistance to therapies designed to inhibit glucose metabolism.     

Plant genome sequencing: applications for crop improvement

DNA sequencing technology is undergoing a revolution with the commercialization of second generation technologies capable of sequencing thousands of millions of nucleotide bases in each run. The data explosion resulting from this technology is likely to continue to increase with the further development of second generation sequencing and the introduction of third generation single‐molecule sequencing methods over the coming years. The question is no longer whether we can sequence crop genomes which are often large and complex, but how soon can we sequence them? Even cereal genomes such as wheat and barley which were once considered intractable are coming under the spotlight of the new sequencing technologies and an array of new projects and approaches are being established. The increasing availability of DNA sequence information enables the discovery of genes and molecular markers associated with diverse agronomic traits creating new opportunities for crop improvement. However, the challenge remains to convert this mass of data into knowledge that can be applied in crop breeding programs.     

Cytokinin dehydrogenase: a genetic target for yield improvement in wheat

The plant hormone group, the cytokinins, is implicated in both qualitative and quantitative components of yield. Cytokinins have opposing actions in shoot and root growth—actions shown to involve cytokinin dehydrogenase (CKX), the enzyme that inactivates cytokinin. We revise and provide unambiguous names for the CKX gene family members in wheat, based on the most recently released wheat genome database, IWGSC RefSeq v1.0 & v2.0. We review expression data of CKX gene family members in wheat, revealing tissue‐specific gene family member expression as well as sub‐genome‐specific expression. Manipulation of CKX in cereals shows clear impacts on yield, root growth and orientation, and Zn nutrition, but this also emphasizes the necessity to unlink promotive effects on grain yield from negative effects of cytokinin on root growth and uptake of mineral nutrients, particularly Zn and Fe. Wheat is the most widely grown cereal crop globally, yet is under‐research compared with rice and maize. We highlight gaps in our knowledge of the involvement of CKX for wheat. We also highlight the necessity for accurate analysis of endogenous cytokinins, acknowledging why this is challenging, and provide examples where inadequate analyses of endogenous cytokinins have led to unjustified conclusions. We acknowledge that the allohexaploid nature of bread wheat poses challenges in terms of uncovering useful mutations. However, we predict TILLING followed by whole‐exome sequencing will uncover informative mutations and we indicate the potential for stacking mutations within the three genomes to modify yield components. We model a wheat ideotype based on CKX manipulation.     

A new mechanism in plant engineering: The potential roles of microRNAs in molecular breeding for crop improvement

MicroRNAs (miRNAs) are small, endogenous, noncoding RNAs that negatively modulate the expression of genes by inhibiting translation or by promoting the degradation of target mRNAs. miRNAs are now known to have greatly expanded roles in a variety of plant developmental processes, in signal transduction, and in the response to environmental stress and pathogen invasion. Because of their ability to inactivate either specific genes or entire gene families, artificial miRNAs function as dominant suppressors of gene activity when brought into a plant. Consequently, miRNA-based manipulations have emerged as promising new approaches for the improvement of crops. This includes the development of breeding strategies and the genetic modification of agronomic traits. Herein, we highlight new findings regarding the roles of miRNAs in plant traits, and describe the current miRNA-based plant engineering approaches. Finally, we consider the feasibility of modulating current approaches to address future challenges such as breeding programs to increase crop yield.     

Prohibitin: a potential target for new therapeutics

Prohibitin (PHB) is localized to the mitochondria where it might have a role in the maintenance of mitochondrial function and protection against senescence. There is considerable controversy concerning the function of nuclear-localized PHB. PHB has potential roles as a tumor suppressor, an anti-proliferative protein, a regulator of cell-cycle progression and in apoptosis. PHB might also function as a cell-surface receptor for an as-yet unidentified ligand. Cell-associated PHB in the gastrointestinal tract has been implicated in protection against infection and inflammation and the induction of apoptosis in other tissues. The diverse array of functions of PHB, together with the emerging evidence that its function can be modulated specifically in certain tissues, suggest that targeting PHB would be a useful therapeutic approach for the treatment of variety of disease states, including inflammation, obesity and cancer.     

Sucrose accumulation in developing peach fruit

Uptake of ¹⁴C-sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring ¹⁴C-sucrose and ¹⁴C-glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 m M ¹⁴C-sucrose and ¹⁴C-glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.
At 10 m M , glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m -chlorophenylhydrazone (CCCP) at 25 μ M. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.
Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly.