Phytosulfokine-α Promotes Root Growth by Repressing Expression of Pectin Methylesterase Inhibitor (PMEI) Genes in Medicago truncatula

Abstract

Phytosulfokine-α (PSK-α), a sulfated pentapeptide with the sequence YIYTQ, is encoded by a small precursor gene family in Arabidopsis. PSK-α regulates multiple growth and developmental processes as a novel peptide hormone. Despite its importance, functions of PSK-α in <i>M. truncatula</i> growth remains unknown. In this study, we identified five genes to encode PSK-α precursors in <i>M. truncatula</i>. All of these precursors possess conserved PSK-α signature motif. Expression pattern analysis of these <i>MtPSK</i> genes revealed that each gene was expressed in a tissue-specific or ubiquitous pattern and three of them were remarkably expressed in root. Treatment of <i>M. truncatula</i> seedlings with synthetic PSK- α peptide significantly promoted root elongation. In addition, expression analysis of downstream genes by RNA-seq and qRT-PCR assays suggested that PSK-α signaling might regulate cell wall structure via PMEI-PME module to promote root cell growth. Taken together, our results shed light on the mechanism by which PSK-α promotes root growth in <i>M. truncatula</i>, providing a new resource for improvement of root growth in agriculture.