GERMIN3 plays a role in plasmodesmatal gating to regulate meristem activation related to tuberisation, tuber dormancy release and stem branching in potato

Summary GERMIN3 has previously been identified as a target of the tuberigen activation complex suggesting a function in potato tuberisation but its role is presently unknown. To understand the role of GERMIN3 we analysed morphological, agronomic and molecular phenotypes in transgenic lines. GERMIN3 over-expressing lines of Solanum tuberosum ssp. andigena exhibited increased tuber yields under permissive conditions and enhanced tuber numbers. Post-harvest tuber sprouting exhibited reduced apical dominance with increased numbers of sprouts. Apical dominance was reduced in aerial tissues of mature plants where stem growth from axillary buds was activated. Similar results were observed in the commercial cultivar Desiree. Over-expression of GERMIN3 had no impact on the expression of SP6A , a positive regulator of tuberisation or TFL1B , a negative regulator. The GERMIN3 protein localised to the endoplasmic reticulum and transient expression in N. benthamiana leaves resulted in plasmodesmatal gating allowing intercellular transport of GFP-tagged sporamin independent of GERMIN3 oxalate oxidase activity. GERMIN3 affects tuberisation and other developmental processes by facilitating meristem activation. This identifies GERMIN3 as a novel protein associated with control of plasmodesmatal transport and supports the importance of plasmodesmatal gating in the regulation of key potato developmental processes.