Involved in the regulation of xylem development and growth. May regulate secondary wall formation during vascular development by modulation of brassinosteroid, gibberellin and auxin hormone signaling pathways. Expressed in vascular tissues of cotyledons, rosette leaves, sepals, petals, anther filaments. Expressed in roots, inflorescence stems and developing seeds. Collapsed xylem vessels in the inflorescence stems. Plants overexpressing VUP1 exhibit severe dwarfism with extreme short and round shaped organs, and display extreme longevity before senescence.