A peptide hormone required for Casparian strip diffusion barrier formation in Arabidopsis roots

Abstract

Plants achieve mineral ion homeostasis by means of a hydrophobic barrier on endodermal cells called the Casparian strip, which restricts lateral diffusion of ions between the root vascular bundles and the soil. We identified a family of sulfated peptides required for contiguous Casparian strip formation in Arabidopsis roots. These peptide hormones, which we named Casparian strip integrity factor 1 (CIF1) and CIF2, are expressed in the root stele and specifically bind the endodermis-expressed leucine-rich repeat receptor kinase GASSHO1 (GSO1)/SCHENGEN3 and its homolog, GSO2. A mutant devoid of CIF peptides is defective in ion homeostasis in the xylem. CIF genes are environmentally responsive. Casparian strip regulation is not merely a passive process driven by root developmental cues; it also serves as an active strategy to cope with adverse soil conditions.

Cell-Fate Specification in Arabidopsis Roots Requires Coordinative Action of Lineage Instruction and Positional Reprogramming

“…Recently, two stele-derived peptides (CASPARIAN STRIP INTEGRITY FACTORS) were identified to move from stele outward to induce Casparian strip formation. Although CASPARIAN STRIP INTEGRITY FACTORS1/2 is unlikely the regulator of J0571 due to the blocked apoplastic path by Casparian strip, there might exist other uncharacterized factors from the stele that affect J0571 expression (Doblas et al, 2017;Nakayama et al, 2017). Interestingly, disruption of symplastic communication between stele and the outer cell layers did not entirely abolish J0571 expression.…”

Uncovering Gene Regulatory Networks Controlling Plant Cell Differentiation

“…Interestingly, SGN1 expression is diminished in a myb36 mutant while SGN3 is relatively unaffected, suggesting that different mechanisms exist for regulating expression of these key receptors [50]. Recently, two complementary efforts uncovered the existence of signaling peptides CASPARIAN STRIP INTERGRATING FACTOR 1 and 2 (CIF1 and CIF2) that act as the ligand for SGN3 to promote CS formation [52,53]. CIF1/2 are produced in the stele, suggesting that CIF1/2 might move from the stele prior to complete CS formation, thereby serving as a SGN3-dependent signal to the endodermis that the root barrier is not yet complete [52,53].…”

Genome-Wide Identification of Medicago Peptides Involved in Macronutrient Responses and Nodulation

“…2B). Underscoring the value of our Focal List, the MtCIF gene was included originally in our Focal List as a predicted PTM-like SSP gene, until homologs of the CIF family were described recently in Arabidopsis and demonstrated to produce a bioactive SSP regulating Casparian strip formation (Doblas et al, 2017;Nakayama et al, 2017). The Focal List thus represents a rich source of leads for future research.…”

“…A number of SSPs have been found to serve as ligands of cell surface receptor kinases (Tabata et al, 2014;Ou et al, 2016;Santiago et al, 2016;Shinohara et al, 2016;Doblas et al, 2017;Nakayama et al, 2017) and function in intercellular communication on spatial scales ranging from adjacent cells to distant organs (Okamoto et al, 2016). SSPs often are encoded within a longer protein sequence of about 100 to 200 amino acids called a preproprotein.…”