The Current Status of Plant Tissue Culture

A Rosa canina WUSCHEL-related homeobox gene, RcWOX1, is involved in auxin-induced rhizoid formation

Homeobox (HB) proteins are important transcription factors that regulate the developmental decisions of eukaryotes. WUSCHEL-related homeobox (WOX) transcription factors, known as a plant-specific HB family, play a key role in plant developmental processes. Our previous work has indicated that rhizoids are induced by auxin in rose (Rosa spp.), which acts as critical part of an efficient plant regeneration system. However, the function of WOX genes in auxin-induced rhizoid formation remains unclear. Here, we isolated and characterized a WUSCHEL-related homeobox gene from Rosa canina, RcWOX1, containing a typical homeodomain with 65 amino acid residues. Real-time reverse transcription PCR (qRT-PCR) analysis revealed that RcWOX1 was expressed in the whole process of callus formation and in the early stage of rhizoid formation. Moreover, its expression was induced by auxin treatment. In Arabidopsis transgenic lines expressing the RcWOX1pro::GUS and 35S::GFP-RcWOX1, RcWOX1 was specifically expressed in roots and localized to the nucleus. Overexpression of RcWOX1 in Arabidopsis increased lateral root density and induced upregulation of PIN1 and PIN7 genes. Therefore, we postulated that RcWOX1 is a functional transcription factor that plays an essential role in auxin-induced rhizoid formation.

Crop improvement through tissue culture

Plant tissue culture comprises a set of in vitro techniques, methods and strategies that are part of the group of technologies called plant biotechnology. Tissue culture has been exploited to create genetic variability from which crop plants can be improved, to improve the state of health of the planted material and to increase the number of desirable germplasms available to the plant breeder. Tissue-culture protocols are available for most crop species, although continued optimization is still required for many crops, especially cereals and woody plants. Tissueculture techniques, in combination with molecular techniques, have been successfully used to incorporate specific traits through gene transfer. In vitro techniques for the culture of protoplasts, anthers, microspores, ovules and embryos have been used to create new genetic variation in the breeding lines, often via haploid production. Cell culture has also produced somaclonal and gametoclonal variants with crop-improvement potential. The culture of single cells and meristems can be effectively used to eradicate pathogens from planting material and thereby dramatically improve the yield of established cultivars. Large-scale micropropagation laboratories are providing millions of plants for the commercial ornamental market and the agricultural, clonally-propagated crop market. With selected laboratory material typically taking one or two decades to reach the commercial market through plant breeding, this technology can be expected to have an ever increasing impact on crop improvement as we approach the new millenium.

History of plant tissue culture

Plant tissue culture, or the aseptic culture of cells, tissues, organs, and their components under defined physical and chemical conditions in vitro, is an important tool in both basic and applied studies as well as in commercial application. It owes its origin to the ideas of the German scientist, Haberlandt, at the begining of the 20th century. The early studies led to root cultures, embryo cultures, and the first true callus/tissue cultures. The period between the 1940s and the 1960s was marked by the development of new techniques and the improvement of those that were already in use. It was the availability of these techniques that led to the application of tissue culture to five broad areas, namely, cell behavior (including cytology, nutrition, metabolism, morphogenesis, embryogenesis, and pathology), plant modification and improvement, pathogen-free plants and germplasm storage, clonal propagation, and product (mainly secondary metabolite) formation, starting in the mid-1960s. The 1990s saw continued expansion in the application of the in vitro technologies to an increasing number of plant species. Cell cultures have remained an important tool in the study of basic areas of plant biology and biochemistry and have assumed major significance in studies in molecular biology and agricultural biotechnology. The historical development of these in vitro technologies and their applications are the focus of this chapter.

Chemicals from roots, hairy roots, and their application

Plants produce thousands of different compounds through the secondary metabolism pathways. Since many of these products are obtained by direct extraction from plants that are cultivated in the field or some times even collected in their original habitat several factors can alter their yield. The use of plant cell cultures has overcome several inconveniences for the production of secondary metabolites. Organized cultures, and especially root cultures, can make a significant contribution to our understanding of secondary metabolism. Furthermore, a new alternative has arisen: transformed root cultures. Until now, hairy roots have been obtained from more than 100 different species. The products that they are able to produce range from alkaloids to aromatic compounds and dyes. These kinds of cultures have turned out to be an invaluable tool to study the biochemistry and the gene expression of the metabolic pathways in order to elucidate the intermediaries and enzymes involved in the biosynthesis of secondary metabolites.