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Sugar-end defect is a tuber quality disorder and persistent problem for the French fry processing industry that causes unacceptable darkening of one end of French fries. This defect appears when environmental stress during tuber growth increases post-harvest vacuolar acid invertase activity at one end of the tuber. Reducing sugars produced by invertase form dark-colored Maillard reaction products during frying. Acrylamide is another Maillard reaction product formed from reducing sugars and acrylamide consumption has raised health concerns worldwide. Vacuolar invertase gene (VInv) expression was suppressed in cultivars Russet Burbank and Ranger Russet using RNA interference to determine if this approach could control sugar-end defect formation. Acid invertase activity and reducing sugar content decreased at both ends of tubers. Sugar-end defects and acrylamide in fried potato strips were strongly reduced in multiple transgenic potato lines. Thus vacuolar invertase silencing can minimize a long-standing French fry quality problem while providing consumers with attractive products that reduce health concerns related to dietary acrylamide.

Advances in charophycean and seedless plant phylogeny, together with progress in our understanding of the genetic control of meristem determination and function that is derived from analysis of higher plant mutants, set the stage for an improved understanding of fundamental aspects of plant body development and evolution. In this article, we have defined 11 early plant body plan innovations, identified issues that require further study and genes that may illuminate them, and suggested organismal systems likely to prove informative.

Polarized membrane trafficking during plant cytokinesis and cell expansion are critical for plant morphogenesis, yet very little is known about the molecular mechanisms that guide this process. Dynamin and dynamin-related proteins are large GTP binding proteins that are involved in membrane trafficking. Here, we show that two functionally redundant members of the Arabidopsis dynamin-related protein family, ADL1A and ADL1E, are essential for polar cell expansion and cell plate biogenesis. adl1A-2 adl1E-1 double mutants show defects in cell plate assembly, cell wall formation, and plasma membrane recycling. Using a functional green fluorescent protein fusion protein, we show that the distribution of ADL1A is dynamic and that the protein is localized asymmetrically to the plasma membrane of newly formed and mature root cells. We propose that ADL1-mediated membrane recycling is essential for plasma membrane formation and maintenance in plants.

Acrylamide is produced in a wide variety of carbohydrate‐rich foods during high‐temperature cooking. Dietary acrylamide is a suspected human carcinogen, and health concerns related to dietary acrylamide have been raised worldwide. French fries and potato chips contribute a significant proportion to the average daily intake of acrylamide, especially in developed countries. One way to mitigate health concerns related to acrylamide is to develop potato cultivars that have reduced contents of the acrylamide precursors asparagine, glucose and fructose in tubers. We generated a large number of silencing lines of potato cultivar Russet Burbank by targeting the vacuolar invertase gene VInv and the asparagine synthetase genes StAS1 and StAS2 with a single RNA interference construct. The transcription levels of these three genes were correlated with reducing sugar (glucose and fructose) and asparagine content in tubers. Fried potato products from the best VInv/StAS1/StAS2‐triple silencing lines contained only one‐fifteenth of the acrylamide content of the controls. Interestingly, the extent of acrylamide reduction of the best triple silencing lines was similar to that of the best VInv‐single silencing lines developed previously from the same potato cultivar Russet Burbank. These results show that an acrylamide mitigation strategy focused on developing potato cultivars with low reducing sugars is likely to be an effective and sufficient approach for minimizing the acrylamide‐forming potential of French fry processing potatoes.

Potato (Solanum tuberosum) is the third most important food crop in the world. Potato tubers must be stored at cold temperatures to prevent sprouting, minimize disease losses, and supply consumers and the processing industry with high-quality tubers throughout the year. Unfortunately, cold storage triggers an accumulation of reducing sugars in tubers. High-temperature processing of these tubers results in dark-colored, bitter-tasting products. Such products also have elevated amounts of acrylamide, a neurotoxin and potential carcinogen. We demonstrate that silencing the potato vacuolar acid invertase gene VInv prevents reducing sugar accumulation in cold-stored tubers. Potato chips processed from VInv silencing lines showed a 15-fold acrylamide reduction and were light in color even when tubers were stored at 4°C. Comparable, low levels of VInv gene expression were observed in cold-stored tubers from wild potato germplasm stocks that are resistant to cold-induced sweetening. Thus, both processing quality and acrylamide problems in potato can be controlled effectively by suppression of the VInv gene through biotechnology or targeted breeding.

Dynamin and dynamin-like proteins are GTP-binding proteins involved in vesicle trafficking. In soybean, a 68-kD dynamin-like protein called phragmoplastin has been shown to be associated with the cell plate in dividing cells (Gu and Verma, 1996). Five ADL1 genes encoding dynamin-like proteins related to phragmoplastin have been identified in the completed Arabidopsis genome. Here we report that ADL1Ap is associated with punctate subcellular structures and with the cell plate in dividing cells. To assess the function of ADL1Ap we utilized a reverse genetic approach to isolate three separate Arabidopsis mutant lines containing T-DNA insertions in ADL1A. Homozygous adl1A seeds were shriveled and mutant seedlings arrested soon after germination, producing only two leaf primordia and severely stunted roots. Immunoblotting revealed that ADL1Ap expression was not detectable in the mutants. Despite the loss of ADL1Ap, the mutants did not display any defects in cytokinesis, and growth of the mutant seedlings could be rescued in tissue culture by the addition of sucrose. Although these sucrose-rescued plants displayed normal vegetative growth and flowered, they set very few seeds. Thus, ADL1Ap is critical for several stages of plant development, including embryogenesis, seedling development, and reproduction. We discuss the putative role of ADL1Ap in vesicular trafficking, cytokinesis, and other aspects of plant growth.

Storing potato tubers at low temperatures helps to minimize losses from sprouting and disease but often leads to an accumulation of reducing sugars in a process called cold-induced sweetening. When tubers with increased amounts of reducing sugars are processed at high temperatures, as by frying, they produce dark-colored, bitter-tasting products that contain elevated amounts of acrylamide, a neurotoxin and possible carcinogen. Transgenic potato tubers with decreased levels of vacuolar invertase (VInv), which converts sucrose from starch breakdown to the reducing sugars glucose and fructose, accumulate fewer reducing sugars during cold-induced sweetening than tubers with higher VInv levels. In this study, the characteristics of tubers in which the vacuolar invertase gene VInv was silenced using RNA-interference were investigated with regard to temperature-dependent sucrose and reducing sugar accumulation, chip color and expression of temperature-responsive genes during long-term cold storage. VInv transcript accumulation and enzyme activity in transgenic tubers were lower than those in control tubers at 3-9°C, but transcript accumulation of other sugar-metabolism genes was largely unaffected by invertase silencing. Chips made from transgenic tubers were paler in color than those from untransformed tubers, and transgenic tubers had lower reducing sugar contents. Tuber sucrose contents were higher in transformed lines than in controls. Responses of sugar contents and transcript levels to tuber storage temperature, time in storage and invertase expression shed light on the regulation of sugar metabolism in stored potato tubers.

Polyploidy is remarkably common in the plant kingdom and polyploidization is a major driving force for plant genome evolution. Polyploids may contain genomes from different parental species (allopolyploidy) or include multiple sets of the same genome (autopolyploidy). Genetic and epigenetic changes associated with allopolyploidization have been a major research subject in recent years. However, we know little about the genetic impact imposed by autopolyploidization. We developed a synthetic autopolyploid series in potato (Solanum phureja) that includes one monoploid (1x) clone, two diploid (2x) clones, and one tetraploid (4x) clone. Cell size and organ thickness were positively correlated with the ploidy level. However, the 2x plants were generally the most vigorous and the 1x plants exhibited less vigor compared to the 2x and 4x individuals. We analyzed the transcriptomic variation associated with this autopolyploid series using a potato cDNA microarray containing 9000 genes. Statistically significant expression changes were observed among the ploidies for 10% of the genes in both leaflet and root tip tissues. However, most changes were associated with the monoploid and were within the twofold level. Thus, alteration of ploidy caused subtle expression changes of a substantial percentage of genes in the potato genome. We demonstrated that there are few genes, if any, whose expression is linearly correlated with the ploidy and can be dramatically changed because of ploidy alteration.

Accumulation of reducing sugars during cold storage is a persistent and costly problem for the potato (Solanum tuberosum L.) processing industry. High temperature processing of potato tubers with elevated amounts of reducing sugars results in potato chips, fries, and other products that are unacceptable to consumers because of their bitter taste and unappealing dark color. More problematically, such products contain increased amounts of acrylamide, a neurotoxin and a potential carcinogen. We have demonstrated that silencing of the potato vacuolar acid invertase gene VInv can prevent reducing sugar accumulation in cold-stored tubers. Using this approach we developed VInv silencing lines using RNA interference (RNAi) from four potato cultivars grown currently for potato chip production in North America. Accumulation of reducing sugars during cold storage was reduced by ∼93% or more in all RNAi lines that had >90% reduction of VInv transcript. Potato chips produced from these lines were light colored and significantly lower in acrylamide than controls. Changes in growth and tuber yield were not associated with VInv suppression using RNAi. We demonstrate that silencing of VInv is an effective approach to control the cold-induced sweetening problem in potato.

Seedlings of Arabidopsis thaliana (L.) Heynh. (Landsberg erecta) were examined by light and electron microscopy to study vascular development through the transition region. In addition, the primary vasculature of the rosette and its relation to that of the root-hypocotyl-cotyledon unit were examined. The transition region is restricted to a very short portion of the upper hypocotyl, the cotyledonary node, and the cotyledons. For most of its length, the hypocotyl is rootlike in vascular arrangement, with a diarch xylem oriented in the exarch condition and an alternate arrangement of the xylem and phloem. The appearance of a pith interrupting the primary xylem plate marks the beginning of vascular transition. Slightly above this level, the phloem strands on either side of the primary xylem plate bifurcate, forming four phloem strands. Moving upward through the cotyledonary node, two phloem strands become spatially associated with each of the xylem groups, forming the traces of the cotyledons. The transition from exarch to endarch xylem is completed in the midveins in the lower portion of the cotyledons. As they ascend the midveins, the two phloem strands assume a position opposite the endarch xylem; the bundles now are almost collateral. About a third of the length into the midveins the phloem strands come to lie side by side, completing transition. By the sixth day, a vascular cambium is initiated from periclinal divisions of procambial cells between the phloem strands and primary xylem plate in the upper hypocotyl and corresponding portion of the cotyledonary node. With interpolation of secondary vascular tissues between the primary phloem and primary xylem, the primary vasculature is disrupted. The vascular system of the rosette develops after the primary vascular system of the root-hypocotyl-cotyledon unit and is superimposed on the latter. Each rosette leaf trace is connected to traces of two other leaves, including the cotyledons, lower on the axis.