Next Generation Sequencing Facilitates Quantitative Analysis of PSKγ1ox and control Transcriptomes

Phytosulfokine-α (PSK-α), a sulfated pentapeptide hormone with the sequence YIYTQ, plays important roles in many aspects of plant growth and development. In this study, we identified a pair of putative precursor genes in soybean, GmPSKγ1 and -2, encoding a PSK-like peptide: PSK-γ. Similar to PSK-α in amino acid composition, the sequence of PSK-γ is YVYTQ, and the tyrosines undergo sulfonylation. Treatment of Arabidopsis seedlings with synthetic sulfated PSK-γ significantly enhanced root elongation, indicating that PSK-γ might be a functional analog of PSK-α. Expression pattern analysis revealed that the two GmPSKγ genes, especially GmPSKγ1, are primarily expressed in developing soybean seeds. Heterologous expression of GmPSKγ1 under the control of a seed-specific promoter markedly increased seed size and weight in Arabidopsis, and this promoting effect of PSK-γ on seed growth was further confirmed in transgenic tobacco constitutively expressing GmPSKγ1. Cytological analysis of transgenic Arabidopsis seeds revealed that PSK-γ promotes seed growth by inducing embryo cell expansion. In addition, transcriptome analysis of GmPSKγ1-expressing Arabidopsis seeds suggested that PSK-γ signaling may regulate cell wall loosening to promote cell expansion. Overall, our results shed light on the mechanism by which PSK-γ promotes seed growth, paving the way for the use of this new peptide for biotechnological improvement of crop seed/grain size and yield. Seed (10 DAP) transcriptomes of OLEOp:GmPSKγ1 and OLEOp:GmPSKγ1tc (control) were generated by deep sequencing using Illumina Hiseq 2500. RNA isolated from three individual lines of each genotype were pooled together for sequencing.