Browsing by Author "Kunert, Karl"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Deleterious effects of plant cystatins against the banana weevil Cosmopolites sordidus
    (Published in Collaboration with the Entomological Society of America, 2010) Kiggundu, Andrew; Muchwezi, Josephine; Van der Vyver, Christell; Viljoen, Altus; Vorster, Juan; Schluter, Urte; Kunert, Karl; Michaud, Dominique
    The general potential of plant cystatins for the development of insect-resistant transgenic plants still remains to be established given the natural ability of several insects to compensate for the loss of digestive cysteine protease activities. Here we assessed the potential of cystatins for the development of banana lines resistant to the banana weevil Cosmopolites sordidus, a major pest of banana and plantain in Africa. Protease inhibitory assays were conducted with protein and methylcoumarin (MCA) peptide substrates to measure the inhibitory efficiency of different cystatins in vitro, followed by a diet assay with cystatin-infiltrated banana stem disks to monitor the impact of two plant cystatins, oryzacystatin I (OC-I, or OsCYS1) and papaya cystatin (CpCYS1), on the overall growth rate of weevil larvae. As observed earlier for other Coleoptera, banana weevils produce a variety of proteases for dietary protein digestion, including in particular Z-Phe-Arg-MCA-hydrolyzing (cathepsin L–like) and Z-Arg-Arg-MCA-hydrolyzing (cathepsin B–like) proteases active in mildly acidic conditions. Both enzyme populations were sensitive to the cysteine protease inhibitor E-64 and to different plant cystatins including OsCYS1. In line with the broad inhibitory effects of cystatins, OsCYS1 and CpCYS1 caused an important growth delay in young larvae developing for 10 days in cystatin-infiltrated banana stem disks. These promising results, which illustrate the susceptibility of C. sordidus to plant cystatins, are discussed in the light of recent hypotheses suggesting a key role for cathepsin B–like enzymes as a determinant for resistance or susceptibility to plant cystatins in Coleoptera.
  • Thumbnail Image
    Item
    Isolation and characterisation of a banana CYCD2;1 gene and its over-expression enhances root growth
    (African Journal of Biotechnology, 2012) Talengera, David; Beemster, Gerrit T.S.; Tushemereirwe, Wilberforce K.; Kunert, Karl
    Stimulation of the cell cycle by over-expression of Arabidopsis CyclinD2;1 enhanced growth in tobacco and rice, but not Arabidopsis. To broaden the range of species and to improve an important crop species for developing countries, a CyclinD2;1 homologue was isolated from an East African highland banana cultivar ‘Nakasabira’ (Musa spp., AAA group) and designated Musac;CYCD2;1 (Genebank accession no HQ839770). Musac;CYCD2;1 amino-acid sequence exhibited 40, 54, 57 and 57% identity with CYCD2;1 sequences of Arabidopsis, rice, maize and wheat, respectively. Over-expression of Musac;CYCD2;1 driven by the CaMV 35S promoter in cultivar ‘Sukali ndizi’ (AAB) resulted in transformed plants with no significant increase in total banana CYCD2;1 transcripts in the shoot, but up to 66-fold increase of total banana CYCD2;1 transcripts in roots. Correspondingly, transformed plants had no change in above-ground growth but produced longer main roots and more lateral roots under in vitro conditions. A deeper root system was observed in one transgenic line relative to non-transformed plants when grown in soil. Results demonstrate that a banana homologue of Arabidopsis CYCD2;1 can also enhance growth in a homologous background and the potential of enhancing banana root growth.