Heterologous expression of stevia SrERF5 inhibits root growth in Arabidopsis thaliana

Stevia is primarily propagated through stem cuttings, and root growth in cuttings is vital for stevia to survive in the field. However, the genetic regulatory mechanism governing the root growth of stevia cuttings has not been fully elucidated to date. In this study, we isolated the AP2/ERF transcription factor SrERF5, which is a member of the B-3 subfamily with a typical AP2 domain. We observed that SrERF5 is specifically localized in the nucleus and exhibits relatively weak transactivation activity in yeast cells. The transcript of SrERF5 was determined to predominantly accumulate in roots and leaves, but was only detected at low levels in flowers, nodes and internodes. The transcription level of SrERF5 was elevated in the process of rooting and subsequently decreased at the late developmental stage. Constitutive expression of SrERF5 in Arabidopsis was observed to partly inhibit primary root growth through regulation of the expression levels of YUC genes. Taken together, the results of our study indicate that SrERF5 is a root growth modulator and may help to elucidate the regulatory mechanism and breeding manipulation of the rooting of stem cuttings in Stevia rebaudiana. This study was the first to isolate and functionally characterize a rooting-related AP2/ERF transcription factor in stevia, and this protein may represent a candidate essential regulator of root development in stem cuttings.