Ectopic expression of class 1 KNOX genes induce and adventitious shoot regeneration and alter growth and development of tobacco (Nicotiana tabacum L) and European plum (Prunus domestica L)

Authors: Srinivasan, Chinnathambi; Liu, Zongrang; Scorza, Ralph

Submitted to: Plant Cell Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2010
Publication Date: 1/7/2011
Citation: Srinivasan, C., Liu, Z., Scorza, R. 2011. Ectopic expression of class 1 KNOX genes induce and adventitious shoot regeneration and alter growth and development of tobacco (Nicotiana tabacum L) and European plum (Prunus domestica L). Plant Cell Reports. 30:655-664.

Interpretive Summary: Shoot regeneration in vitro from cultured organ pieces of plum is an important step in producing transgenic plum with economically useful genes. Clonal regeneration of shoots from cultured leaves of plum is difficult to achieve. In order to make plum leaves regeneratively-competent to produce shoots in vitro, we have transformed plum hypocotyls sections with regeneration inducing genes, such as KNOX1 genes from apple, to produce transgenic plum shoots with regeneration inducing genes. We have also produced transgenic tobacco with apple KNOX1 genes to serve as a model plant. Apple KNOX1 altered growth and development of both tobacco and plum. Tobacco leaves transformed with apple KNOX1 gene regenerated shoots without cytokinin, a growth regulator in the culture medium. Cultured leaves from KNOX1 gene expressing plum required synthetic cytokinin to regenerate shoots. This research showed that regeneration of plums can be improved, and this aids in the development of new, adapted plum cultivars.

Technical Abstract: Transgenic plants of tobacco (Nicotiana tabacum L) and plum (Prunus domestica L) were produced by transforming with apple class 1 KNOX genes (MdKN1 and MdKN2) or corn KN1 gene. Transgenic tobacco plants were regenerated in vitro from transformed leaf discs cultured in a tissue medium lacking cytokinin. Ectopic expression of KNOX genes retarded shoot growth by suppressing elongation of internodes in tobacco. When over-expressed, all three KNOX genes induced malformation of leaves by severe reduction in leaf lamina expansion and extensive lobing in tobacco, but in plum only, MdKN1 caused reduction in shoot growth and leaf malformation. In situ regeneration of adventitious shoots was observed from leaves and roots of transgenic tobacco plants expressing KNOX genes. In vitro culture of leaf explants and stem sections excised from in vitro grown MdKN1 expressing tobacco shoots regenerated adventitious shoots on Murashiege and Skoog (MS) basal medium without exogenous cytokinin. However, leaf explants excised from in vitro grown shoots of MdKN1 over-expressing plum required 7.5 uM thidiazuron in the culture medium for adventitious shoot regeneration.