PIP2, An Auxin Induced Plant Peptide Hormone Regulates Root and Hypocotyl Elongation in Arabidopsis

Abstract

Auxin is one of the traditional plant hormones, whereas peptide hormones are peptides with hormone activities. Both auxin and plant peptide hormones regulate multiple aspects of plant growth and development, and there are cross-talks between auxin and plant peptide hormones. PAMP-INDUCED SECRETED PEPTIDES (PIPs) and PIP-LIKEs (PIPLs) are a new family of plant peptide hormone, and PIPL3/TARGET OF LBD SIXTEEN 2 (TOLS2) has been shown to regulate lateral root formation in <i>Arabidopsis</i>. We report here the identification of <i>PIP2</i> as an auxin response gene, and we found it plays a role in regulating root and hypocotyl development in <i>Arabidopsis</i>. By using quantitative RT-PCR, we found that the expression of <i>PIP2</i> but not <i>PIP1</i> and <i>PIP3</i> was induced by auxin, and auxin induced expression of <i>PIP2</i> was reduced in <i>nph4-1</i> and <i>arf19-4</i>, the lost-of-function mutants of <i>Auxin Response Factor 7</i> (<i>ARF7</i>) and <i>ARF19</i>, respectively. By generating and characterizing overexpressing transgenic lines and gene edited mutants for <i>PIP2</i>, we found that root length in the <i>PIP2</i> overexpression plant seedlings was slightly shorter when compared with that in the Col wild type plants, but root length of the <i>pip2</i> mutant seedlings remained largely unchanged. For comparison, we also generated overexpressing transgenic lines and gene edited mutants for <i>PIP3</i>, as well as <i>pip2 pip3</i> double mutants. Surprisingly, we found that root length in the <i>PIP3</i> overexpression plant seedlings is shorter than that of the <i>PIP2</i> overexpression plant seedlings, and the <i>pip3</i> mutant seedlings also produced short roots. However, root length in the <i>pip2 pip3</i> double mutant seedlings is largely similar to that in the <i>pip3</i> single mutant seedlings. On the other hand, hypocotyl elongation assays indicate that only the <i>35S:PIP2</i> transgenic plant seedlings produced longer hypocotyls when compared with the Col wild type seedlings. Further analysis indicates that PIP2 promotes cell division as well as cell elongation in hypocotyls. Taken together, our results suggest that <i>PIP2</i> is an auxin response gene, and PIP2 plays a role in regulating root and hypocotyl elongation in <i>Arabidopsis</i> likely <i>via</i> regulating cell division and cell elongation.