CANDIDATE HORMONE-RESPONSIVE MARKERS FOR CALLOGENESIS OF OIL PALM (Elaeis guineensis Jacq.)

The in vitro propagation of the oil palm involves an indirect somatic embryogenesis process through an intervening callogenesis phase. Both processes are determining factors in the success of clonal propagation. This study aims to discover expression markers associated with hormone response as a means to measure the favourable response of oil palms to callogenesis. Expression levels of hormone responsive genes in cultured and uncultured leaf explants were measured by using quantitative real time PCR, followed by statistical analysis to determine whether a relationship to callogenesis existed. The potential for callogenesis in cultured leaf explants of oil palms was significantly correlated to the expression changes of a putative brassinosteroid leucine-rich repeat (LRR) receptor kinase (EgBrRK), a putative cytokinin dehydrogenase (EgCKX) and a putative response regulator type A gene (EgRR1). A regression model for callogenesis incorporating these three genes indicated a predicted R-2 value of 67.89%. The larger reduction in the expression of EgRR1 and another cytokinin responsive gene, EgCK REGULATED KINASE, in cultures exhibiting higher callogenesis rates suggested an increase in cytokinin signalling output and cytokinin levels. This inference was supported by a slight decrease in the expression of EgCKX, suggesting a mild reduction in cytokinin degradation in these cultures. The use of these markers for the prediction of callogenesis rate in uncultured and one-day cultured leaf explants, may provide an early assessment of the callogenesis potential of oil palms.