Biosynthesis of nicotine in tobacco requires N-methylputrescine oxidase (MPO), which belongs to the copper-containing amine oxidase superfamily. Previous studies identified tobacco MPO1 and its close homolog NtDAO1 (formerly called MPO2), of which MPO1 has been shown preferentially to oxidize N-methylated amines. We show here that NtDAO1, as well as a homologous Arabidopsis diamine oxidase (DAO), accept non-N-methylated amines more efficiently than their corresponding N-methylated amines. MPO1 is coordinately regulated with other nicotine biosynthesis genes with regard to COI1-MYC2-dependent jasmonate induction and its dependence on nicotine-specific ERF transcription factors, whereas NtDAO1 is constitutively expressed at low basal levels in tobacco plants. Both MPO1 and NtDAO1 are targeted to peroxisomes by their C-terminal motifs, and the peroxisomal localization of MPO1 is required for it to function in nicotine biosynthesis in jasmonate-elicited cultured tobacco cells. Restricted occurrence of the MPO subfamily in Nicotiana and Solanum indicates that, during the formation of the Solanaceae, MPO has evolved from a DAO, which functions in polyamine catabolism within peroxisomes, by optimizing substrate preference and gene expression patterns to be suitable for alkaloid formation.

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AbstarctRegulation of storage root development by source strength remains largely unknown. The cassava storage root delay (srd) T-DNA mutant postpones storage root development but manifests normal foliage growth as wild-type plants. The SRD gene was identified as an orthologue of α-glucan, water dikinase 1 (GWD1), whose expression is regulated under conditions of light/dark cycles in leaves and is associated with storage root development. The GWD1-RNAi cassava plants showed both retarded plant and storage root growth, as a result of starch excess phenotypes with reduced photosynthetic capacity and decreased levels of soluble saccharides in their leaves. These leaves contained starch granules having greatly increased amylose content and type C semi-crystalline structures with increased short chains that suggested storage starch. In storage roots of GWD1-RNAi lines, maltose content was dramatically decreased and starches with much lower phosphorylation levels showed a drastically reduced β-amylolytic rate. These results suggested that GWD1 regulates transient starch morphogenesis and storage root growth by decreasing photo-assimilation partitioning from the source to the sink and by starch mobilization in root crops.

Cassava (Manihot esculenta Crantz) is one of the most important crops of Thailand. Its storage roots are used as food, feed, starch production, and be the important source for biofuel and biodegradable plastic production. Despite the importance of cassava storage roots, little is known about the mechanisms involved in their formation. This present study has focused on comparison of the expression profiles of cassava root proteome at various developmental stages using two-dimensional gel electrophoresis and LC-MS/MS. Based on an anatomical study using Toluidine Blue, the secondary growth was confirmed to be essential during the development of cassava storage root. To investigate biochemical processes occurring during storage root maturation, soluble and membrane proteins were isolated from storage roots harvested from 3-, 6-, 9-, and 12-month-old cassava plants. The proteins with differential expression pattern were analysed and identified to be associated with 8 functional groups: protein folding and degradation, energy, metabolism, secondary metabolism, stress response, transport facilitation, cytoskeleton, and unclassified function. The expression profiling of membrane proteins revealed the proteins involved in protein folding and degradation, energy, and cell structure were highly expressed during early stages of development. Integration of these data along with the information available in genome and transcriptome databases is critical to expand knowledge obtained solely from the field of proteomics. Possible role of identified proteins were discussed in relation with the activities during storage root maturation in cassava.

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As a major staple food source in Africa and other tropical developing countries, cassava (Manihot esculenta) provides basic sustenance for many subsistence farmers. However, cassava roots mainly accumulate starch with limited contribution of other nutrients such as proteins and vitamins. Also, two viral diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), cause great losses in cassava production in subSaharan Africa and the Indian sub-continent. Genetic engineering provides promising approaches to improve nutritional value and increase resistance to viral diseases in cassava. This report presents several successful case studies on engineering protein content by overexpression of nutritious storage proteins and improving cassava resistance to viral diseases by RNA interference. Perspectives on the sustainable acquisition of new knowledge and development of biotechnology to solve these bottlenecks are discussed.