Practice question

Cells inherently possessing embryogenic potential without need for prolonged dedifferentiation are designated pre embryogenic determined cells PEDCs conceptualized by Sharp et al. They exist in tissues retaining embryonic character such as nucellus, immature zygotic embryo protoderm, shoot apical meristem periphery and leaf epidermis of certain species. Epigenetically PEDCs maintain open chromatin at promoters of master regulators SOMATIC EMBRYOGENESIS RECEPTOR KINASE1 SERK1 BABY BOOM BBM LEAFY COTYLEDON1 LEC1 and WUSCHEL, with low DNA methylation allowing rapid transcriptional activation. Upon minimal inductive stimulus like transient auxin pulse or osmotic stress they divide embryogenically generating suspensor like structure and polarized embryo directly. This contrasts with induced embryogenic determined cells IEDCs requiring high 2,4-D exposure to remodel chromatin and suppress vegetative programs. Presence of PEDCs explains genotype dependent responsiveness and explant specificity of direct somatic embryogenesis systems. Exploiting PEDCs facilitates efficient transformation because transgene integration occurs before first division ensuring uniform transgenic embryos avoiding chimerism and reducing time to regenerated plantlets suitable for commercial micropropagation and artificial seed technology.