InterPro domain: IPR045021

This family represents the plant-specific proteins PSI 1-3 (Protein PSK SIMULATOR 1-3) from Arabidopsis. These proteins promote plant growth, especially at the vegetative stage, probably via the regulation of phytosulfokine (PSK) signalling; PSKs are peptide phytohormones acting as growth factors [ 1 ]. They are required during vegetative growth and reproduction, PSI1 acts predominantly at the seedling stage whereas PSI2 and 3 are required for vegetative growth where they act synergistically. PSI1 and 3 may also have a function in carbohydrate metabolism [ 2 ].

1. The PSI family of nuclear proteins is required for growth in arabidopsis. Plant Mol. Biol. 86, 289-302