Investigation of the cambium regulators for the secondary growth and organogenesis in Raphanus sativus L

Abstract

Raphanus sativus or radish is one of the most socioeconomically important root crops in northeast Asia. Radish root develops an edible thick storage root whose growth has been proven to be caused by cell division in the cambium. Although the radish genome has been studied and compared to other members of the Brassicaceae, its broad comprehension is yet to be completed. In this research, we looked at the radish root gene expression during its key development periods, 5, 7 and 9 weeks post seed planting, in two phenotypically different radish lines. We identified conserved cambium regulators as well as new cambium enriched genes that might play a novel function in the vascular cambium. Additionally, we discovered the ability of the radish cambium to reprogram itself to produce adventitious roots (AR). To further understand this process, we investigated how auxin induces AR formation in radish. We found that the auxin-induced WOX11/12 molecular pathway that produces AR in Arabidopsis, also plays an important role in radish AR formation, thus confirming the evolutionary conservation of the pathway. We also analyzed how cambium secondary growth regulators change their expression during AR organogenesis. Interestingly, we found that RsWOX4and RsPXY, key regulators of cambium cell division, change their expression pattern seemingly to aid the vascularization of the AR primordium. This thesis provides an overview of the molecular dynamics in radish taproot cambium, alternative functions of the cambium.