This review highlights the years of research on the genetics of in vitro regeneration in higher plants conducted at the Department of Genetics and Biotechnology of Saint Petersburg State University. The genetic collection of radish (Raphanus sativus) created at the department by selfing of individual plants from three cultivars was used as a model in these studies. Some radish inbred lines from the genetic collection form spontaneous tumors in the roots and are also used to study mechanisms of tumor growth in higher plants. It was revealed that radish lines that differed in the ability to form tumors also contrastingly differed in the reaction of their explants to auxin and cytokinin in vitro, which reflects a difference in the levels of these hormones in the tissues of related tumorous and non-tumorous radish lines. Moreover, high concentrations of cytokinins in cultural medium induced tumor formation in the regenerated plants of tumorous radish lines. The presence of meristematic zones in spontaneous tumors in radish lines, as well as in crown gall tumors induced by Agrobacterium tumefaciens and cytokinin-induced tumors made it possible to reveal the role of the main meristem regulators, such as KNOX and WOX family transcription factors and the CLAVATA system, in both the process of tumor growth and regeneration in plants. Analysis of the expression of meristem-specific genes during the development of spontaneous and induced tumors in radish as well as in regenerated radish plants confirmed this assumption.

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Genetic control of regeneration processes of radish plants in vitro: from phenotype to genotype.

Several inbred lines from a radish (Raphanus sativus var. Radicula Pers.) genetic collection spontaneously form tumors on the crop roots during flowering. Here we studied the influence of the Agrobacterium tumefaciens ipt gene, which controls cytokinin biosynthesis, and the Agrobacterium rhizogenes rolC gene, which influences cytokinin metabolism, on tumor formation in the radish lines. Two in planta transformation methods – transformation of ovaries via pollen-tube pathway and transformation of seedling apexes – were firstly used to obtain transgenic radish plants. Both methods showed high efficiency for radish. Transformation of radish lines by both ipt and rolC genes induced tumor formation in non-tumorous lines. We noted a several-fold increase of free zeatin concentration in ipt-transgenic radish plants while rolC-transgenic radish plants showed an increase in zeatin riboside concentration comparing with the untransformed line. We suppose that the tumorigenic effect of ipt and rolC genes on radish lines is likely to be due to change of phytohormonal balance in the tissues of transgenic plants.

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Influence of Agrobacterium tumefaciens ipt and Agrobacterium rhizogenes rolC Genes on Spontaneous Tumor Formation and Endogenous Cytokinins Content in Radish (Raphanus sativus) Inbred Lines

Veronika A. Monakhova

Papers

Influence of Agrobacterium tumefaciens ipt and Agrobacterium rhizogenes rolC Genes on Spontaneous Tumor Formation and Endogenous Cytokinins Content in Radish (Raphanus sativus) Inbred Lines