Genetic and metabolic control of grain shape and weight in wheat
Final Report Abstract
This project aims to analyse mechanisms determining grain size and grain weight of two winter wheat models, the introgression line W-IL and the transgenic line HOSUT, over-expressing a sucrose transporter from barley. Both models display increased seed size compared to their basis lines Prinz and Certo, respectively. Increased grain size in the W-IL line probably derived from the maternal tissues pericarp/integuments/nucellus whereas the HOSUT-grains could be altered in endosperm development. These hypotheses should be confirmed in this project by applying histological characterisation, comprehensive phenotypic analysis and investigation of the molecular and metabolic network. Due to restricted time and resources, the foreseen analysis was predominantly restricted to the HOSUT/Certo model. Histological analysis shows altered development of HOSUT caryopses compared to the base line Certo. It was concluded that HOSUT endosperm growth is lower at early prestorage phases but is increased during grain filling stage. The stimulated growth potentially applies to endosperm and especially to the lobes of the endosperm. This is confirmed by the fact that caryopses thickness rather than width is higher in the HOSUT caryopses. The increased endosperm size in HOSUT probably results from an increased endosperm cell number. Moreover, endopolyploidisation, which is a direct measure for cell elongation and the degree of differentiation, is lower in the HOSUT endosperm. Together, this suggests that the larger endosperm in the developing HOSUT caryopses contains a higher number of smaller cells. For the W-IL line it was shown that its endosperm contains larger cells compared to Prinz, which is probably the reason for the larger endosperm size. Thus, the findings for the line W-IL are clearly different from the results from the HOSUT24/Certo, where the increased endosperm is probably due to a higher number of cells. Micro-dissected endosperm tissue was chosen for a comparative transcript profiling between HOSUT and Certo grains using 60k AGILENT wheat microchip. Preliminary data evaluation of differentially expressed genes reveals over-represented categories in the early HOSUT endosperm related to growth and development. Especially those genes are up-regulated, which are involved in cell cycle regulation suggesting stimulated cell division activity in the HOSUT endosperm. Transcript profiling further points to the concerted action of auxin and gibberellin functions in order to promote cell division within the HOSUT endosperm cells by up-regulating cell cycle regulation genes. Overall, it is concluded that overexpressing the sucrose transporter increases sucrose uptake capacity in HOSUT endosperm and leads to stimulation of mitotic activity in the endosperm. Such sugar effects on mitotic activity are well known and could partially be mediated by sucrose activation of cyclin D-type gene expression. Confirmatively, three members of D-cyclins are transcriptionally up-regulated in the early HOSUT endosperm.
Publications
- (2013) Diverse accumulation and distribution of nutrient elements in developing wheat grain studied by laser ablation inductively coupled plasma mass spectrometry imaging. Metallomics 5, 1276-1284
Wu, B., Andersch, F., Weschke, W., Weber, H., Becker, JS.
(See online at https://doi.org/10.1039/c3mt00071k) - (2014) Increased grain yield and micronutrient concentration in transgenic winter wheat by ectopic expression of a barley sucrose transporter. J. of Cereal Science 60, 75-81
Saalbach, I., Mora-Ramirez, I., Weichert, N., Andersch, F., Guild, G., Wieser, H., Koehler, P., Stangoulis, J., Kumlehn, J., Weschke, W., Weber, H.
(See online at https://doi.org/10.1016/j.jcs.2014.01.017)
