Archiv der bisher stattgefundenen Seminare

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Abstract: Kiwifruit is one of the most recent successful fruit crops on the market. Alongside the well-known green-fleshed Actinidia chinensis var. deliciosa ‘Hayward’, other species with different flavour, shape and colour (yellow and red) have been used in breeding programmes to develop new cultivars. Novel coloured kiwifruit are attractive to consumers, but achieving uniform fruit pigmentation, particularly in red-fleshed Actinidia chinensis var. chinensis genotypes, is challenging. Colour inconsistency between fruit can affect consumer perception, lowering returns to growers. To investigate the cause of colour inconsistency we focused on a solid red-fleshed genotype characterised by variable outer pericarp red pigmentation, we hypothesised that the carbohydrate supply could be responsible for the variation of the red flesh colour. Early in fruit development (28 days after anthesis, DAA) we adjusted the leaf-to-fruit ratio of the shoots to two different carbohydrate supplies (standard and low). Carbohydrate import or redistribution outside of the shoot was controlled by applying a girdle at the base of the shoot, and this girdle was maintained open until harvest to guarantee long-term control of carbohydrate supply. From 84 DAA we observed a reduction in fruit size by about 30 percent, dry matter was reduced by more than 20 percent and colour development by more than 80 percent when fruit had low carbohydrate supply. Both anthocyanin and carbohydrate metabolites were affected. The concentration of major non-structural carbohydrates (starch, glucose, sucrose, and fructose) were also reduced by more than 50 percent in fruit with low carbohydrate supply from 84 DAA. A minor sugar, galactose, was also dramatically reduced by low carbohydrate supply. By 112 DAA, total anthocyanin concentration in the outer pericarp of fruit with low carbohydrate supply was reduced by more than 80 percent. Despite these significant changes in fruit development and metabolites, transcription for candidate genes considered critical steps in the anthocyanin biosynthetic pathway (i.e. GT1, MYB10 and bHLH5) were unchanged between fruit with the two carbohydrate supplies. Interestingly, in low carbohydrate supply fruit, a vacuolar invertase gene (INV3) was upregulated at 112 DAA and a beta-amylase gene (BAM9) was upregulated at 84 and 112 DAA. The upregulation of these two genes could be correlated to the low carbohydrate supply available to the fruit and the need to deplete the starch stored in the fruit to support further development. This work suggested a link between carbohydrate and anthocyanin metabolism, and we now have two further hypothesis to test: i) Galactose is the glycosyl moiety of the main kiwifruit anthocyanin measured in these fruit, and given that galactose content was affected by low carbohydrate supply, repression of colour development could be due to substrate limitation; and/or ii) Carbohydrate depletion could have an effect on an unknown repressor of the anthocyanin pathway. We are currently performing a transcriptomic (RNAseq) experiment to test these hypotheses and results should be available soon. [mehr]

Starch is a vital plant product, being the major nutritive component of our staple crops and an important feedstock for industry. Starch takes the form of insoluble, semi-crystalline granules composed of two glucose polymers: branched amylopectin and near-linear amylose. Amylopectin, the major component, is responsible for the semi-crystalline nature of starch. It is made by a set of enzymes; starch synthases, branching enzymes and debranching enzymes. In contrast, amylose is made within the amylopectin matrix by a single enzyme – Granule-Bound Starch Synthase (GBSS) – that becomes trapped as amylopectin crystalizes about it. There is much that we still do not understand about starch biosynthesis, such as how the enzyme activities are coordinated and how starch granules are first initiated. We recently discovered that a new class of proteins is required to localize some of the Starch Synthase activities. We called these proteins PTST (for Protein Targeting to Starch). Arabidopsis has three PTSTs. PTST1 binds GBSS and delivers it to the starch granule surface, whereupon it dissociates and leaves GBSS to synthesise amylose. In the absence of PTST1, GBSS fails to localize to the granule and the starch is composed solely of amylopectin. In contrast, PTST2 and PTST3 bind to another starch synthase, SS4, which is implicated in starch granule initiation. Defects in SS4 or in PTST2/3 significantly alter the number, size and shape of starch granules without necessarily affecting the structure or ratio of the constituent polymers. We believe that these PTSTs bind low-abundance precursors from a pool of malto-oligosaccharides and deliver them to SS4 for elaboration into starch granule initials. In this talk I will summarize these and other results which shed new light onto how plants make starch. [mehr]

Abstract: During reproduction the mother plant uses environmental signals to modulate the dormancy and behaviour of her progeny seeds. This presentation will explore the importance of this process in plant evolutionary biology, and discuss what is known about the underlying molecular mechanisms. Key data will point to an ancient role of flowering time genes in seed biology, which may precede the co-option of these genes into reproductive processes that evolved later, such as flowering itself. Using natural variation to study seed dormancy I will raise the prospect that a parental conflict exists at the heart of seed dormancy and growth vigour, and therefore that mothers and fathers have different optimised fates for progeny seeds. We can speculate a bit as to why this might be and the implications for crop science. [mehr]

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Ascorbic acid (vitamin C) is a major antioxidant in plants, and fruits are the major source of this vitamin for humans. While the pathways of synthesis, recycling and degradation are well characterized, their regulation is still poorly understood. We have used reverse genetic approaches to target two key steps of the Wheeler & Smirnoff synthesis pathway: GDP-D-mannose epimerase (GME) and GDP-L-galactose phosphorylase (GGP) in tomato fruits. In addition to a reduction of ascorbic acid content, RNAi-silenced gme tomato lines exhibited growth phenotypes resulting from cell division and expansion defects, exacerbated fragility and loss of fruit firmness related to modifications of the cell wall structure and composition [1,2]. These findings help to explain observed links between seemingly unrelated quality traits such as fruit firmness and ascorbic acid content. Two ggp knockout lines were identified from TILLING (EMS) mutant populations. These have reduced ascorbic content and show bleaching and leaf necrosis after short exposure to high light [3,4]. Integration of transcriptomic, proteomic, and metabolomic data from wild type and mutant tomato fruits identified candidate genes involved in the regulation of the ascorbate pathway [5]. A forward genetic screen has identified four mutant lines which have 2.5 to 5-fold higher levels of ascorbic acid than wild-type, and one candidate gene has been mapped using next generation sequencing approaches. [1] Gilbert L, Alhagdow M, Nunes-Nesi A, Quemener B, Guillon F, Bouchet B, Faurobert M, Gouble B, Page D, Garcia V, Petit J, Stevens R, Causse M, Fernie AR, Lahaye M, Rothan C and Baldet P. (2009). Plant J. 60, 499-508. [2] Voxeur A, Gilbert L, Rihouey C, Driouich A, Rothan C, Baldet P and Lerouge P (2011). Journal of Biological Chemistry, 286: 8014-8020. [3] Okabe Y, Asamizu E., Saito T., Matsukura C., Ariizumi T., Bres C., Rothan C., Mizoguchi T. and Ezura H. (2011). Plant Cell Physiol. 52(11): 1994–2005. [4] Just D., Garcia V., Fernandez L., Bres C., Mauxion JP., Petit J., Jorly J., Assali J., Bournonville C., Ferrand C., Baldet P., Lemaire-Chamley M., Mori K., Okabe Y., Ariizumi T., Asamizu E., Ezura H., and Rothan C. (2013). Plant Biotech. 30, 225-231. [5] Garcia V., Stevens R., Gil L., Gilbert L., Gest N., Petit J., Faurobert M., Maucourt M., Deborde C., Moing A., Poessel JL., Jacob D., Bouchet JP., Giraudel JL., Gouble B., Page D., Alhagdow M., Massot C., Gautier H., Lemaire-Chamley M., de Daruvar A., Rolin D., Usadel B., Lahaye M., Causse M., Baldet P. and Rothan C. (2009). Compte rendu de Biologie. 332, 1007-1021. [mehr]

In order to feed an ever-increasing world population, there needs to be a step-change in the way new, more productive varieties are developed. Monitoring of plant growth and composition is being transformed by new imaging methods. Nondestructive measurements mean that individual plants can be followed over time, giving new insights into phenotypic plasticity and developmental change. Focussing on the important crop plants sorghum and cassava, I will present unpublished and published results on how we are using whole plant phenomics and FT-IR and Raman imaging to analyse the costs and benefits of specialised metabolites, focussing on cyanogenic glucosides in Sorghum from our EMS-TILLING population. Ros Gleadow is an ecophysiologist interested in secondary compounds, who has been using the Adelaide phenotyping facility for her work. A recent publication of hers on this is: http://jxb.oxfordjournals.org/content/early/2015/02/18/jxb.eru526.abstract A description of the acyanogenic mutants and the TILLING project can be found here: http://onlinelibrary.wiley.com/doi/10.1111/j.1467-7652.2011.00646.x/abstract [mehr]