Highlights d Lateral root founder cells (LRFCs) express TOLS2 peptide, inhibiting nearby LRFCs d The receptor RLK7 and transcription factor PUCHI make up the TOLS2 signaling pathway d DR5, an LRFC marker, is occasionally activated in proximity to pre-existing LRFCs d TOLS2-RLK7-PUCHI inhibits LRFC identity in proximal cells, ensuring proper LR spacing SUMMARYIn plants, the position of lateral roots (LRs) depends on initiation sites induced by auxin. The domain of high auxin response responsible for LR initiation stretches over several cells, but only a pair of pericycle cells (LR founder cells) will develop into LRs.In this work, we identified a signaling cascade controlling LR formation through lateral inhibition. It comprises a peptide hormone TARGET OF LBD SIXTEEN 2 (TOLS2), its receptor RLK7, and a downstream transcription factor PUCHI. TOLS2 is expressed at the LR founder cells and inhibits LR initiation. Time-lapse imaging of auxin-responsive DR5:LUCIFERASE reporter expression revealed that occasionally two pairs of LR founder cells are specified in close proximity even in wild-type and that one of them exists only transiently and disappears in an RLK7-dependent manner. We propose that the selection of LR founder cells by the peptide hormone-receptor cascade ensures proper LR spacing.

Summary Lateral root (LR) formation in Arabidopsis thaliana is initiated by asymmetric division of founder cells, followed by coordinated cell proliferation and differentiation for patterning new primordia. The sequential developmental processes of LR formation are triggered by a localized auxin response. LATERAL ORGAN BOUNDARIES‐DOMAIN 16 (LBD16), an auxin‐inducible transcription factor, is one of the key regulators linking auxin response in LR founder cells to LR initiation. We identified key genes for LR formation that are activated by LBD16 in an auxin‐dependent manner. LBD16 targets identified include the transcription factor gene PUCHI, which is required for LR primordium patterning. We demonstrate that LBD16 activity is required for the auxin‐inducible expression of PUCHI. We show that PUCHI expression is initiated after the first round of asymmetric cell division of LR founder cells and that premature induction of PUCHI during the preinitiation phase disrupts LR primordium formation. Our results indicate that LR initiation requires the sequential induction of transcription factors LBD16 and PUCHI.

SUMMARYLateral root (LR) formation is important for the establishment of root architecture in higher plants. Recent studies have revealed that LR formation is regulated by an auxin signaling pathway that depends on auxin response factors ARF7 and ARF19, and auxin/indole-3-acetic acid (Aux/IAA) proteins including SOLITARY-ROOT (SLR)/IAA14. To understand the molecular mechanisms of LR formation, we isolated a recessive mutant rlf (reduced lateral root formation) in Arabidopsis thaliana. The rlf-1 mutant showed reduction of not only emerged LRs but also LR primordia. Analyses using cell-cycle markers indicated that the rlf-1 mutation inhibits the first pericycle cell divisions involved in LR initiation. The rlf-1 mutation did not affect auxin-induced root growth inhibition but did affect LR formation over a wide range of auxin concentrations. However, the rlf-1 mutation had almost no effect on auxin-inducible expression of LATERAL ORGAN BOUNDARIES-DOMAIN16/ ASYMMETRIC LEAVES2-LIKE18 (LBD16/ASL18) and LBD29/ASL16 genes, which are downstream targets of ARF7/19 for LR formation. These results indicate that ARF7/19-mediated auxin signaling is not blocked by the rlf-1 mutation. We found that the RLF gene encodes At5g09680, a protein with a cytochrome b 5 -like heme/ steroid binding domain. RLF is ubiquitously expressed in almost all organs, and the protein localizes in the cytosol. These results, together with analysis of the genetic interaction between the rlf-1 and arf7/19 mutations, indicate that RLF is a cytosolic protein that positively controls the early cell divisions involved in LR initiation, independent of ARF7/19-mediated auxin signaling.

Humans in modern industrial and postindustrial societies face sustained challenges from environmental pollutants, which can trigger tissue damage from xenotoxic stress through different mechanisms. Thus, the identification and characterization of compounds capable of conferring antioxidant effects and protection against these xenotoxins are warranted. Here, we report that the natural extract of Polypodium leucotomos named Fernblock®, known to reduce aging and oxidative stress induced by solar radiations, upregulates the NRF2 transcription factor and its downstream antioxidant targets, and this correlates with its ability to reduce inflammation, melanogenesis, and general cell damage in cultured keratinocytes upon exposure to an experimental model of fine pollutant particles (PM2.5). Our results provide evidence for a specific molecular mechanism underpinning the protective activity of Fernblock® against environmental pollutants and potentially other sources of oxidative stress and damage-induced aging.

Tree species of three growth forms (evergreen conifers, deciduous hardwoods, and evergreen hardwoods) codominate at the northern distribution limit of evergreen hardwoods in central Japan. This study examined the stand dynamics and competition during 13 years at a single plot to reveal how three growth forms codominate at the ecotone. Species were characterized as large DBH and low tree density for evergreen conifers, and conversely for evergreen hardwoods. Total basal area increased during the examined period, accompanied with the reduction in tree density (i.e., mortality exceeded the recruitment rate). Mortality increased with time especially for small trees of deciduous hardwoods. The effect of competition among the three growth forms on tree growth was not detected. Species were classified into two axes. Ingrowth and recruitment rates of large evergreen conifers were lower than those of small evergreen hardwoods. The population growth rate was lower in species with greater mortality within each growth form. Deciduous hardwoods showed the highest mortality and lowest population growth rates among the three growth forms. Although the tree‐ring analysis revealed that disturbances occurred to some extent, the current disturbance regime would not trigger the regeneration of deciduous hardwoods. This study suggests that negative relations of maximum DBH with ingrowth and recruitment rates contribute to codominance of evergreen conifers and evergreen hardwoods, and more frequent or larger disturbances than at present are necessary for regeneration of deciduous hardwoods.