Grafting success by cell wall remodeling: Plants that produce great fruit may not always have great roots. Grafting of a productive scion onto a resilient rootstock has provided agriculturalists with solutions to this and other challenges. Notaguchi et al. have now studied why some plant grafts work better than others (see the Perspective by McCann). The tobacco relative Nicotiana benthamiana ( Nb ) turns out to be the superhero of grafting, able to form grafts with plants from a wide range of evolutionary families. A bit of Nb , set as a middleman between a tomato scion and an Arabidopsis rootstock, negotiated a successful junction between these two otherwise nonconversant plant species. The expression of β-1,4-glucanases secreted into the extracellular region turns out to be key in facilitating cell wall reconstruction. Science , this issue p. 698 ; see also p. 618

SNF1-related protein kinases 2 (SnRK2s) are key regulators governing the plant adaptive responses to osmotic stresses, such as drought and high salinity. Subclass III SnRK2s function as central regulators of abscisic acid (ABA) signalling and orchestrate ABA-regulated adaptive responses to osmotic stresses. Seed plants have acquired other types of osmotic stress-activated but ABA-unresponsive subclass I SnRK2s that regulate mRNA decay and promote plant growth under osmotic stresses. In contrast to subclass III SnRK2s, the regulatory mechanisms underlying the rapid activation of subclass I SnRK2s in response to osmotic stress remain elusive. Here, we report that three B4 Raf-like MAP kinase kinase kinases (MAPKKKs) phosphorylate and activate subclass I SnRK2s under osmotic stress. Transcriptome analyses reveal that genes downstream of these MAPKKKs largely overlap with subclass I SnRK2-regulated genes under osmotic stress, which indicates that these MAPKKKs are upstream factors of subclass I SnRK2 and are directly activated by osmotic stress.

Nitrogen (N) and carbon (C) are essential elements for plant growth and crop yield. Thus, improved N and C utilisation contributes to agricultural productivity and reduces the need for fertilisation. In the present study, we find that overexpression of a single rice gene, Oryza sativa plasma membrane (PM) H⁺-ATPase 1 (OSA1), facilitates ammonium absorption and assimilation in roots and enhanced light-induced stomatal opening with higher photosynthesis rate in leaves. As a result, OSA1 overexpression in rice plants causes a 33% increase in grain yield and a 46% increase in N use efficiency overall. As PM H⁺-ATPase is highly conserved in plants, these findings indicate that the manipulation of PM H⁺-ATPase could cooperatively improve N and C utilisation, potentially providing a vital tool for food security and sustainable agriculture.

Acclimation to high temperature increases plants’ tolerance of subsequent lethal high temperatures. Although epigenetic regulation of plant gene expression is well studied, how plants maintain a memory of environmental changes over time remains unclear. Here, we show that JUMONJI (JMJ) proteins, demethylases involved in histone H3 lysine 27 trimethylation (H3K27me3), are necessary for Arabidopsis thaliana heat acclimation. Acclimation induces sustained H3K27me3 demethylation at HEAT SHOCK PROTEIN22 (HSP22) and HSP17.6C loci by JMJs, poising the HSP genes for subsequent activation. Upon sensing heat after a 3-day interval, JMJs directly reactivate these HSP genes. Finally, jmj mutants fail to maintain heat memory under fluctuating field temperature conditions. Our findings of an epigenetic memory mechanism involving histone demethylases may have implications for environmental adaptation of field plants.

Highly efficient tissue repair is pivotal for surviving damage-associated stress. Plants generate callus upon injury to heal wound sites, yet regulatory mechanisms of tissue repair remain elusive. Here, we identified WUSCHEL-RELATED HOMEOBOX 13 (WOX13) as a key regulator of callus formation and organ adhesion in Arabidopsis (Arabidopsis thaliana). WOX13 belongs to an ancient subclade of the WOX family, and a previous study shows that WOX13 orthologs in the moss Physcomitrium patens (PpWOX13L) are involved in cellular reprogramming at wound sites. We found that the Arabidopsis wox13 mutant is totally defective in establishing organ reconnection upon grafting, suggesting that WOX13 is crucial for tissue repair in seed plants. WOX13 expression rapidly induced upon wounding, which was partly dependent on the activity of an AP2/ERF transcription factor, WOUND-INDUCED DEDIFFERENTIATION 1 (WIND1). WOX13 in turn directly upregulated WIND2 and WIND3 to further promote cellular reprogramming and organ regeneration. We also found that WOX13 orchestrates the transcriptional induction of cell wall-modifying enzyme genes, such as GLYCOSYL HYDROLASE 9Bs, PECTATE LYASE LIKEs and EXPANSINs. Furthermore, the chemical composition of cell wall monosaccharides was markedly different in the wox13 mutant. These data together suggest that WOX13 modifies cell wall properties, which may facilitate efficient callus formation and organ reconnection. Furthermore, we found that PpWOX13L complements the Arabidopsis wox13 mutant, suggesting that the molecular function of WOX13 is partly conserved between mosses and seed plants. This study provides key insights into the conservation and functional diversification of the WOX gene family during land plant evolution.