E4-type SUMO ligase that promotes SUMO chain formation in a SCE1-dependent manner and thus contributes to a pathway for proteolytic removal of sumoylation substrates. Involved in stress responses (e.g. osmotic, salt and abscisic acid ABA) and sulfur metabolism. Protein modification; protein sumoylation. Expressed in leaves, stems and flowers, and, at low levels, in siliques and old leaves. No obvious growth difference under standard greenhouse conditions. Altered sulfur metabolism. Reduced growth in high osmotic pressure (mannitol) and in response to abscisic acid (ABA), but enhanced growth and fitness in high salt (NaCl) condition. Abnormal steady state levels of SUMO conjugates in various conditions. Belongs to the PIAL protein ligase family.