Problems and possibilities of monocot transformation

Abstract

Biotechnological improvement of monocots is often hampered by the lack of efficient regeneration systems, requisite wound responses and low cell competence. Despite these limitations, the biolistic and Agrobacterium methods have been successfully used to produce several transgenic monocots by adjusting the parameters that govern efficient delivery and integration of transgene(s) into plant genome. It is now possible to transform even difficult monocots using tailor-made gene constructs and promoters, suitable A. tumefaciens strains and a proper understanding of the entire process. This success has been reviewed in the present article and a special emphasis was laid on the measures that were taken in overcoming the difficulties that arise due to the differential responses of monocots and dicots. This information is necessary for biotechnological improvement of still newer monocotyledonous plants that have been hitherto difficult to transform.

In vitro transformation of pearl millet (Pennisetum glaucum (L). R. BR.): Selection of chlorsulfuron-resistant plants and long term expression of the gus gene under the control of the emu promoter

“…This process is supposedly much higher in monocots (Lambé et al, 1995;Sood et al, 2011). However, in the current study, in contrast to GUS activity, resistance to chlorosulfuron was stably expressed, at least during the first nine months post bombardment, by pearl millet plants regenerated from transformed calli.…”

“…However, several transformation systems leading to the introduction of DNA into monocotyledon intact tissues have been developed: for example electroporation into organized plant tissues (Dekeyser et al, 1990), silicon carbide fiber-mediated DNA transfer into maize suspension cells (Kaeppler et al, 1990;Sood et al, 2011) and the microprojectile bombardment or biolistic method (Klein et al, 1987;Prathibha and Sticklen, 2002;Martinez-Trujillo et al, 2003;Singh et al, 2013). Microprojectile bombardment is currently the most used method for in vitro transformation of graminaceous even if improvements of the Agrobacterium-mediated transformation method have been achieved (Liu et al, 2005;Razzaq et al, 2010;Sharma et al, 2011;Plaza-Wüthrich and Tadele 2012).…”

Efficient regeneration and Agrobacterium-mediated transformation protocol for recalcitrant indica rice (Oryza sativa L.).

“…Wounded tissues of monocots were also found to actively differentiate into lignified or sclerified cells which blocked Agrobacterium from invading the wounded sites. This rapid differentiation of wounded tissues left only a handful of cells marginally transformed (Sood et al, 2011). Ethylene production in response to plant wounding, biotic and abiotic stress has been a common phenomenon (Wang et al, 2002) but the production of this simple two-carbon compound has elicited the host plant response to suppress the activation of Agrobacterium's vir gene.…”

Hairy root biotechnology—indicative timeline to understand missing links and future outlook

“…(6) Exploring the difficulties encountered in Agrobacterium-mediated transformation of monocots, various studies reveal that monocots have differences in cellular structures, wound response, subsequent vir gene induction, etc. (Sood et al 2011). Still the exact molecular phenomenon behind the high susceptibility of dicots over monocot plant species needs the scientific attention; (7) Can there be a possibility to control the natural bacterial host range to avoid loss of productivity simply by knowing the molecular basics of transformation under simulated laboratory conditions?…”