Identification and characterization ofArabidopsis LEC1andLEC2orthologous genes in cassava somatic embryo development(Manihot esculenta, Crantz)
Alejandro Brand1, Mauricio A Quimbaya2 and Paul Chavarriaga1*
1International Center for Tropical Agriculture CIAT, Km 17 Recta Cali-Palmira, Colombia.
2Department of Natural Sciences and Mathematics, Faculty of Engineering, Pontificia Universidad Javeriana Cali, Calle 18 No. 118-250 Cali, Colombia.
*
The development of transgenic technology in cassava has emerged as a promising strategy for crop improvementenabling the introduction of new agronomic traits into the cassava genome. The high degree genotype-dependence, somaclonal variationandlow efficiency production of friable embriogenic callus (FEC) are critical obstacles that limit the incorporation and scaling up of the process of farmer- and industry-preferred landraces into transformation systems. Identifyingthe molecular factors underlying the embryodevelopment in cassava may help to overcome these constraints. In Arabidopsis thaliana, the LEAFY COTYLEDON (LEC) transcription factors (TFs) LEC1 and LEC2 play a fundamental role in the establishment ofa cellular environment that promotes sexual and somatic embryo development, controlling various metabolic pathways of plant embryogenesis. In this study, we identified candidate orthologous genes of LEC1 and LEC2 in cassava, designated as MeLEC1 and MeLEC2, respectively. Relative expression analysis showed that both MeLEC1 and MeLEC2 are present at higher levels in somatic embryogenic tissues in contrast with differentiated mature tissue. The rapid increase in the expression of MeLEC genes at early SE induction times, strongly suggest that they are involved in the transition from a somatic to an embryonic state, and probably in the competence acquisition for SE development in cassava. The cDNAs of both genes were confirmed by sequencing and cloned independently in expression vectors under control ofaconstitutive promoter. MeLEC1 and MeLEC2 overexpression in Arabidopsis and cassava respectively provide clues about their possible role associated with SE. Preliminary results show that 2x35S::MeLEC2 embryos of model cultivar TMS60444 developed somatic embryo-like structures on cotyledons surface and the overexpression appears to repress the vegetative development inhibiting the development progression of cassava embryos. The identification of MeLEC TFs may contribute not only to improve our understanding of SE processes in cassava, but also, it provides tools to optimize genetic transformation processes in this cultivar through development of genotype-independent transformation protocols.