Isopentenyl Transferase and Cytokinin Oxidase/Dehydrogenase Gene Family Members are Differentially Expressed During Pod and Seed Development in Rapid-cycling Brassica

Abstract

The plant hormone group, the cytokinins, regulates many stages of plant growth and development. Regulation includes that of cell division and enhancement of sink strength, both of which are important processes in seed development and embryonic growth. Two gene families play a key role in maintaining cytokinin homeostasis: isopentenyl transferase (IPT), which catalyzes the rate-limiting step in the formation of cytokinins, and cytokinin oxidase/dehydrogenase (CKX), which irreversibly inactivates cytokinins by cleaving the N6 side chain. Quantitative reverse transcriptase polymerase chain reaction (PCR) was used to measure the expression of individual gene family members to investigate the source of cytokinin and its subsequent inactivation during the early stages of seed and pod development. In this study, rapid-cycling Brassica rapa (RCBr) was used because of its genetic relatedness to commercial Brassica species, its rapid life cycle, its small adult size, and its larger reproductive organs compared to Arabidopsis. Our results indicate that BrIPT1, -3, and -5 and BrCKX1, -2, -3, and -5 express differentially both temporally and spatially within RCBr root, stem, leaf, seed, and pod tissues. Particularly strong expression was shown by IPT3 and IPT5 and CKX2 in developing seeds.