The Danger-Associated Peptide PEP1 Directs Cellular Reprogramming in the Arabidopsis Root Vascular System

Abstract

When perceiving microbe-associated molecular patterns (MAMPs) or plant-derived damage-associated molecular patterns (DAMPs), plants alter their root growth and development by displaying a reduction in the root length and the formation of root hairs and lateral roots. The exogenous application of a MAMP peptide, flg22, was shown to affect root growth by suppressing meristem activity. In addition to MAMPs, the DAMP peptide PEP1 suppresses root growth while also promoting root hair formation. However, the question of whether and how these elicitor peptides affect the development of the vascular system in the root has not been explored. The cellular receptors of PEP1, PEPR1 and PEPR2 are highly expressed in the root vascular system, while the receptors of flg22 ( FLS2 ) and elf18 ( EFR ) are not. Consistent with the expression patterns of PEP1 receptors, we found that exogenously applied PEP1 has a strong impact on the division of stele cells, leading to a reduction of these cells. We also observed the alteration in the number and organization of cells that differentiate into xylem vessels. These PEP1-mediated developmental changes appear to be linked to the blockage of symplastic connections triggered by PEP1. PEP1 dramatically disrupts the symplastic movement of free green fluorescence protein (GFP) from phloem sieve elements to neighboring cells in the root meristem, leading to the deposition of a high level of callose between cells. Taken together, our first survey of PEP1-mediated vascular tissue development provides new insights into the PEP1 function as a regulator of cellular reprogramming in the Arabidopsis root vascular system.

How Does Global Warming Sabotage Plant Immunity?

“…Recent studies (Jing et al, 2019;Okada et al, 2021;Poncini et al, 2017) reported that root growth was impaired by perceiving biotic or abiotic stress signals. Consistent with this finding, we also identified that plant elicitor peptide 1 (PEP1), a general sensor of biotic and abiotic stresses, affects the reprograming of Arabidopsis root apical meristem and vascular development (Dhar et al, 2021). In addition, PEP1 strongly impacts the cell-to-cell symplastic connection, which is responsible for transporting developmental signals over a long distance.…”

The molecular framework underlying the growth and defense tradeoff in Arabidopsis roots in response to danger signals

“…However, estradiol-induced STZ-OE line #2 displayed a significant increase of "extra xylem" vessel differentiation as compared to the WT seedlings grown on 10 M estradiol plates (~15% in WT and ~30% in STZ-OE#2) (Figure 3i; S11c and d; Table S11). These STZ-OE phenotypes recapitulate the PEP1-influenced phenotypes of WT, supporting the crucial role of STZ in the PEP-mediated reprogramming of root development (Dhar et al, 2021).…”

“…Indeed, expressing a high dosage of STZ in the root meristem using an estradiol-inducible transactivation system (STZ-OE line #2) resulted in (i) the exhaustion of stem cell niche, (ii) an early and ectopic xylem vessel differentiation, and (iii) aberrant divisions in the QC. These phenotypes are reminiscent of those found in the seedlings treated with PEP1 (Jing et al, 2019;Dhar et al, 2021;Okada et al, 2021). The STZ-OE transgenic line #2 phenotypes are further supported in the RNA-seq analyses.…”

“…STZ-OE #2-5 line exhibited an early and ectopic xylem differentiation (Figure 3h and I; S11) similar to the seedlings treated with PEP1 (Dhar et al, 2021). Therefore, we inquired whether STZ induced developmentally-induced programmed cell death (dPCD) genes.…”

“…We observed a clear reduction of the meristem size as early as 6h after PEP1 treatment (Figure S1a and b). We also reported that PEP1 influences formative divisions of the vascular initials in the meristem (Poncini et al, 2017;Jing et al, 2019;Dhar et al, 2021). To understand the genes and regulatory pathways PEP1 directs for cellular reprogramming in the root meristem, we performed a time-course transcriptome profiling for PEP1-treated root meristems (Figure 1a).…”