Metabolomic and transcriptomic analyses identify external conditions and key genes underlying high levels of toxic glycoalkaloids in tubers of stress-sensitive potato cultivars

Introduction: High levels of toxic steroidal glycoalkaloids (SGAs) in potato tubers constitute a recognized food quality problem. Tuber SGA levels vary between potato cultivars and can increase after post-harvest stresses such as wounding and light exposure. A few cultivars, e.g., 'Magnum Bonum' and 'Lenape,' have been withdrawn from commercial sales due to excessive SGA levels during some cultivation years. However, these sudden SGA increases are diffucult to predict, and their causes are not understood. To identify external and genetic factors that underlie sudden SGA increases in certain potato cultivars, we have here in a 2-year study investigated 'Magnum Bonum' and five additional table potato cultivars for their SGA levels after wounding and light exposure.Results: and methods Results showed that 'Magnum Bonum' has an unusual strong SGA response to light exposure, but not to wounding, whereas 'Bintje' displayed an opposite regulation. Levels of calystegine alkaloids were not significantly altered by treatments, implicating independent metabolic regulation of SGA and calystegine levels also under conditions of high SGA accumulation. Metabolomic and transcriptomic analyses identified a small number of key genes whose expression correlated with SGA differences between cultivars. Overexpression of two key genes in transgenic low-SGA potato cultivars increased their leaf SGA levels significantly.Discussion: The results show that a strong response to light can underlie the SGA peaks that occasionally occur in certain potato cultivars and indicate that a between-cultivar variation in the expression of single SGA key genes can account for cultivar SGA differerences. We propose that current attempts to mitigate the SGA hazard will benefit from an increased consideration of cultivar-dependent SGA responses to post-harvest conditions, particularly light exposure. The identified key SGA genes can now be used as a molecular tool in this work

Improved bioenergy value of residual rice straw by increased lipid levels from upregulation of fatty acid biosynthesis

BackgroundRice (Oryza sativa) straw is a common waste product that represents a considerable amount of bound energy. This energy can be used for biogas production, but the rate and level of methane produced from rice straw is still low. To investigate the potential for an increased biogas production from rice straw, we have here utilized WRINKLED1 (WRI1), a plant AP2/ERF transcription factor, to increase triacylglycerol (TAG) biosynthesis in rice plants. Two forms of Arabidopsis thaliana WRI1 were evaluated by transient expression and stable transformation of rice plants, and transgenic plants were analyzed both for TAG levels and biogas production from straw.ResultsBoth full-length AtWRI1, and a truncated form lacking the initial 141 amino acids (including the N-terminal AP2 domain), increased fatty acid and TAG levels in vegetative and reproductive tissues of Indica rice. The stimulatory effect of the truncated AtWRI1 was significantly lower than that of the full-length protein, suggesting a role for the deleted AP2 domain in WRI1 activity. Full-length AtWRI1 increased TAG levels also in Japonica rice, indicating a conserved effect of WRI1 in rice lipid biosynthesis. The bio-methane production from rice straw was 20% higher in transformants than in the wild type. Moreover, a higher producing rate and final yield of methane was obtained for rice straw compared with rice husks, suggesting positive links between methane production and a high amount of fatty acids.ConclusionsOur results suggest that heterologous WRI1 expression in transgenic plants can be used to improve the metabolic potential for bioenergy purposes, in particular methane production

Differential regulation of Knotted1-like genes during establishment of the shoot apical meristem in Norway spruce (Picea abies)

Establishment of the shoot apical meristem (SAM) in Arabidopsis embryos requires the KNOXI transcription factor SHOOT MERISTEMLESS. In Norway spruce (Picea abies), four KNOXI family members (HBK1, HBK2, HBK3 and HBK4) have been identified, but a corresponding role in SAM development has not been demonstrated. As a first step to differentiate between the functions of the four Norway spruce HBK genes, we have here analyzed their expression profiles during the process of somatic embryo development. This was made both under normal embryo development and under conditions of reduced SAM formation by treatment with the polar auxin transport inhibitor NPA. Concomitantly with the formation of an embryonic SAM, the HBK2 and HBK4 genes displayed a significant up-regulation that was delayed by NPA treatment. In contrast, HBK1 and HBK3 were up-regulated prior to SAM formation, and their temporal expression was not affected by NPA. Ectopic expression of the four HBK genes in transgenic Arabidopsis plants further supported similar functions of HBK2 and HBK4, distinct from those of HBK1 and HBK3. Together, the results suggest that HBK2 and HBK4 exert similar functions related to the SAM differentiation and somatic embryo development in Norway spruce, while HBK1 and HBK3 have more general functions during embryo development

Attityder till kursvärdering

Kursvärdering är ett användbart instrument för att analysera den sammantagna undervisningsprocessen. Genom kursvärdering kan deltagarna göras medvetna om vad som upplevts positivt eller negativt i undervisningen, och en gemensam grund kan utarbetas inför ett kommande förbättringsarbete. Eftersom rollen inom undervisningen är så pass olika för kursledare, lärare och studenter är det tänkbart att dessa skillnader påverkar deras syn på kursvärdering eller behovet av den. Syftet med denna studie har varit att undersöka: i) om det finns skillnader i attityden till kursvärdering bland studenter och lärare, samt ii) hur resultaten av kursvärdering sammanställs, synliggörs och tillämpas inom undervisningen. En enkät om synen på kursvärdering besvarades av 254 studenter resp. 59 lärare inom SLU:s JLT-fakultet1. Resultaten visar att kursvärdering genomförs på alla av fakultetens kurser, och att en kombination av skriftlig och muntlig kursvärdering är den vanligaste formen. Grundsynen till kursvärdering är mycket positiv bland både studenter och lärare, men det finns klara skillnader i vad man är positiv till och till vad man anser som viktigt att utvärdera. Exempelvis visar lärare en klart större vilja än studenter att värdera kursens mål och hur de uppfylldes, och inte bara kursens medel och innehåll. Lärare och studenter visar också klart skilda uppfattningar om vad som innefattas i begreppet ”kursens helhetsintryck”, där man till största delen fokuserar på varandras respektive insatser under kursen. Lärarna anser att kursvärdering ger ett god stöd i planeringsarbetet med nästkommande kurser. Även om kursvärderingsresultaten nästan alltid sammanställs och diskuteras inom lärarkåren, verkar resultaten och de förändringar av kursen de leder till vara otydliga för studenterna. De vanligaste förändringarna föranledda av kursvärdering är direkt relaterade till själva undervisningen, t.ex. ändringar av föreläsningar och laborationer. Mer övergripande organisatoriska frågor om kursen och dess roll i utbildningen verkar inte tas upp i kursvärderingsprocessen. Det samlade intrycket av enkätsvaren ger en bild av kursvärdering inom fakulteten som en relativt väl fungerande process, även om den också kan förbättras. Med de båda enkäterna som grund ges i slutet av arbetet förslag på några enkla förbättringar av kursvärderingsprocessen inom fakulteten

Reduction of Cholesterol and Glycoalkaloid Levels in Transgenic Potato Plants by Overexpression of a Type 1 Sterol Methyltransferase cDNA

Transgenic potato (Solanum tuberosum cv Désirée) plants overexpressing a soybean (Glycine max) type 1 sterol methyltransferase (GmSMT1) cDNA were generated and used to study sterol biosynthesis in relation to the production of toxic glycoalkaloids. Transgenic plants displayed an increased total sterol level in both leaves and tubers, mainly due to increased levels of the 24-ethyl sterols isofucosterol and sitosterol. The higher total sterol level was due to increases in both free and esterified sterols. However, the level of free cholesterol, a nonalkylated sterol, was decreased. Associated with this was a decreased glycoalkaloid level in leaves and tubers, down to 41% and 63% of wild-type levels, respectively. The results show that glycoalkaloid biosynthesis can be down-regulated in transgenic potato plants by reducing the content of free nonalkylated sterols, and they support the view of cholesterol as a precursor in glycoalkaloid biosynthesis