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Inter‐tissue communication is instrumental to coordinating the whole‐body level behaviour for complex multicellular organisms. However, little is known about the regulation of inter‐tissue information exchange. Here we carried out genetic screens for root‐to‐shoot mobile silencing in Arabidopsis plants with a compromised small RNA‐mediated gene silencing movement rate and identified radical‐induced cell death 1 (RCD1) as a critical regulator of root–shoot communication. RCD1 belongs to a family of poly (ADP‐ribose) polymerase proteins, which are highly conserved across land plants. We found that RCD1 coordinates symplastic and apoplastic movement by modulating the sterol level of lipid rafts. The higher superoxide production in rcd1‐knockout plants resulted in lower plasmodesmata (PD) frequency and altered PD structure in the symplasm of the hypocotyl cortex. Furthermore, the mutants showed increased lateral area of tracheary pits, which reduced axial movement. Our study highlights a novel mechanism through which root‐to‐shoot long‐distance signalling can be modulated both symplastically and apoplastically. [ABSTRACT FROM AUTHOR]

VIVIPAROUS1/ABSCISIC ACID INSENSITIVE3-LIKE1 (VAL1) encodes a DNA-binding B3 domain protein and plays essential roles in seed maturation and flowering transition by repressing genes through epigenetic silencing in Arabidopsis. SWI-INDEPENDENT3 (SIN3)-LIKEs (SNLs), which encode scaffold proteins for the assembly of histone deacetylase complexes and have six SIN3 homologues (SNL1–SNL6) in Arabidopsis thaliana, directly repress gene expression to regulate seed maturation and flowering transition. However, it remains unclear whether VAL1 and SNLs work together in repressing the expression of related genes. In this study, yeast two-hybrid and firefly luciferase complementation imaging assays revealed that VAL1 interacts with SNLs, which can be attributed to its own zinc-finger CW (conserved Cys (C) and Trp (W) residues) domain and the PAH (Paired Amphipathic Helices) domains of SNLs. Furthermore, pull-down experiments confirmed that the CW domain of VAL1 interacts with both intact protein and the PAH domains of SNLs proteins, and the co-immunoprecipitation assays also confirmed the interaction between VAL1 and SNLs. In addition, quantitative real-time PCR (qRT-PCR) analysis showed that VAL1 and SNLs were expressed in seedlings, and transient expression assays showed that VAL1 and SNLs were localized in the nucleus. Considered together, these results reveal that VAL1 physically interacts with SNLs both in vitro and in vivo, and suggest that VAL1 and SNLs may work together to repress the expression of genes related to seed maturation and flowering transition in Arabidopsis. [ABSTRACT FROM AUTHOR]

Objectives: The beneficial role of ROS was probably in promoting intercellular communication by modifying membrane constituents [Liang D. A salutary role of reactive oxygen species in intercellular tunnel-mediated communication. Front Cell Dev Biol. 2018;6:2]. We investigated how the membrane lipids were responding to ROS and ROS inhibitors. Methods: To examine how ROS affected the lipid profiles, we used thin-layer chromatography to characterize lipid profiles in Arabidopsis plants. Then, the confocal microscopy imaging was used to confirm the change of membrane lipid in a plasma membrane marker line exposed to ROS and ROS inhibitors. Results: We found the relative contents of most lipids in H2O2-treated Arabidopsis plants were increased in roots, rather than in shoots. The increased fluorescent signal of membrane marker induced by H2O2 was mainly enriched in the conductive parts of roots. Several ROS inhibitors also strongly affected the lipid profiles. Among them, diethyldithiocarbamate (DDC) can progressively change the lipid profiles with treatment going on. Membrane marker signal was mainly accumulated in the root tips and epidermal cells after treatment by DDC. Discussion: H2O2 may enhance intercellular communication by inducing different lipid species in the conductive parts of roots. The lipid profiles were widely responding to various ROS reagents and might play a role in intercellular signaling. [ABSTRACT FROM AUTHOR]

Scion-rootstock union formation is a critical step toward the functional assemblage of heterogeneous plants. Interfamilial scion-rootstock interaction often results in graft incompatibility during the assemblage process, and the underlying mechanisms are largely unknown. In this study, we reported that tracheary element (TE) remodeling, including TE segmentation and deformation, rather than de novo formation from callus or adjacent tissues, took place at the early stage of grafting interface between Arabidopsis thaliana and Nicotiana benthamiana (At / Nb). Following cellular deposits, the short TEs from both partners were overlapping, dependent on the homogeneity of contacting TEs, with each other. Without overlapping, the TEs at the interface would grow laterally, and the TEs above and below the interface would undergo self-fusion to form insulating spiraling bundles. Finally, the overlapping TEs constituted a continuous network through alignment. Our results provide a definitive framework for the critical process of TE behavior in the At / Nb distant grafts, including (1) segmentation and/or deformation, (2) matching, overlapping, and cellular deposits, and (3) aligning or spiraling. These insights might guide us in the future into constructing more compatible distant grafts from the perspective of TE homogeneity. [ABSTRACT FROM AUTHOR]

A broad‐spectrum, catalytic method has been developed for the synthesis of sulfonamides and sulfamates. With the activation by the combination of a catalytic amount of 1‐hydroxybenzotriazole (HOBt) and silicon additives, amidations of sulfonyl fluorides and fluorosulfates proceeded smoothly and excellent yields were generally obtained (87–99 %). Noticeably, this protocol is particularly efficient for sterically hindered substrates. Catalyst loading is generally low and only 0.02 mol % of catalyst is required for the multidecagram‐scale synthesis of an amantadine derivative. In addition, the potential of this method in medicinal chemistry has been demonstrated by the synthesis of the marketed drug Fedratinib via a key intermediate sulfonyl fluoride 13. Since a large number of amines are commercially available, this route provides a facile entry to access Fedratinib analogues for biological screening. [ABSTRACT FROM AUTHOR]

Self-incompatibility in Brassicaceae is determined by the interaction between S-Locus Protein 11 (SP11) on the pollen and S-receptor kinase (SRK) in the stigma. Pollen from heterozygotes generally displays products of both SP11 alleles, but in some heterozygotes SP11 expression is monoallelic, with one allele (SP11 R ) being silenced by promoter methylation. An exciting development in understanding the mechanism behind monoallelic silencing came recently when Y. Tarutani et al. [Nature 2010;466:983–986] identified a 24-nucleotide sRNA (termed Smi) derived from a non-coding gene within the dominant S-haplotype, and suggested that Smi directs promoter methylation. We propose that rather than having a direct effect on DNA methylation, Smi is the first step in a novel cis-acting siRNA pathway that directs widespread monoallelic SP11 R promoter methylation. [ABSTRACT FROM AUTHOR]

Abstract: BREVIS RADIX is a novel plant-specific gene family with highly conserved protein sequences; the key member of this family, BRX, controls cell proliferation and root elongation in Arabidopsis. In this study, six members of rice BRX-like gene family containing the conserved BRX domain were identified in japonica rice. Phytogenetic analysis suggested that BRX-like genes may be evolved before the divergence of vascular plant and bryophytes species. Four rice BRX-like genes were predominantly (OsBRXL1, OsBRXL2, and OsBRXL4) or specifically (OsBRXL3) expressed in young panicle. Except one member (OsBRXL6) that was not expressed in all the tissues and organs investigated, the other five genes were differentially responsive to major stresses including drought, salt, and cold, suggesting that the BRX-like family may also function in abiotic stress responses. OsBRXL1 and OsBRXL4 were significantly up-regulated by brassinosteroid and auxin, respectively. To further test the function of BRX-like genes in rice, the OsBRXL4 was overexpressed in rice Zhonghua 11. The OsBRXL4-overexpression plant showed significantly longer root and increased sensitivity to auxin than wild type, suggesting that OsBRXL4 may be involved in primary root growth through the auxin signaling pathway. [Copyright &y& Elsevier]

Root-derived mobile signals play critical roles in coordinating a shoot's response to underground conditions. However, the identification of root-to-shoot long-distance mobile signals has been scant. In this study, we aimed to characterize root-to-shoot endogenous mobile miRNAs by using an Arabidopsis/Nicotiana interfamilial heterograft in which these two taxonomically distant species with clear genetic backgrounds had sufficient diversity in differentiating miRNA sources. Small RNA deep sequencing analysis revealed that 82 miRNAs from the Arabidopsis scion could travel through the graft union to reach the rootstock, whereas only a very small subset of miRNA (6 miRNAs) preferred the root-to-shoot movement. We demonstrated in an ex vivo RNA imaging experiment that the root-to-shoot mobile Nb-miR164, Nb-miR395 and Nb-miR397 were targeted to plasmodesmata using the bacteriophage coat protein MS2 system. Furthermore, the Nb-miR164 was shown to move from the roots to the shoots to induce phenotypic changes when its overexpressing line was used as rootstock, strongly supporting that root-derived Nb-miR164 was able to modify the scion trait via its long-distance movement. [ABSTRACT FROM AUTHOR]

Vascular connection is key to successful graft. Little study has been devoted to the behavior of tracheary elements (TEs), the basic component of vascular bundles, during vascular connection between scion and rootstock. Here we report the structural changes of TEs at the graft interface between two quinoa cultivars, Qaidam White-1 (QW1) and Qaidam Red-1 (QR1). Our results showed that TEs in ungrafted plants developed following an ontogenetic sequence, i.e., the annular vessel, helical vessel, scalariform vessel, reticulate vessel, and pitted vessel. However, this process was greatly accelerated in grafted plants, resulting in quick developmental transition of TE wall patterning. At the early stage of intraspecific grafting (e.g., 5 days after grafting), the membrane-like cellular patches were heavily accumulated at the graft interface but quickly retreated within 2–4 days, suggesting an early emergency response to grafting. The TE length in both scion and rootstock was significantly shorter (more than 50% on average, n TE = 747) than the ungrafted plants in the same period. These short TEs were gradually integrated into a long, continuous conduit, thereby enabling the functional vasculature at the graft union. In addition, the pit size was gradually reduced, for example, for the surface area of outer pit aperture, from 12.73 ± 3.15 to 5.40 ± 0.30 μm2, or for the surface area of inner pit aperture, from 9.34 ± 3.33 to 1.96 ± 1.04 μm2, in 18 days (n pits = 2830). Taken together, the morphological changes of TEs and cellular responses to grafting in the intraspecific grafts seemed to be conservative to other homografts and heterografts, implying that these behavioral changes are highly adaptive to the scion–rootstock interaction. • Grafting accelerated developmental transition of TE (tracheary element) wall patterning in quinoa interspecific graft. • Membrane-like cellular deposits occurred as early as 5 DAG and quickly decreased within 2–4 days. • Short TEs accumulated at the graft interface. • Short TEs were integrated into long, continuous conduit. • Pit size (diameter and area) decreased with grafting time going on. [ABSTRACT FROM AUTHOR]

In distantly-related plant grafting, incompatibility often occurs between scion and rootstock, resulting in growth stagnation, and eventually graft failure. In this study, we found that an emergent structure, or the spiraling tracheary element (TE) bundles consisting of TE masses occurring at the graft interface, was extensively present in the highly incompatible interfamilial graft of Brassica napus/Portulaca oleracea ( Bn/Po ) and Nicotiana benthamiana / Portulaca oleracea ( Nb / Po ). This special structure mostly appeared in the local area near the grafting union, and the frequency and quantity of the spiraling tracheary element bundles were much higher in the scion than in the rootstock. Nevertheless, only a small portion of Arabidopsis thaliana / Portulaca oleracea ( At/Po ) interfamilial grafts showed a less spiraled TEs at the grafting union (usually a circular TE), which is consistent with its growth performance. This study consolidated that spiraling TE bundles were an important indicator for graft incompatibility. The possible reason for the formation of spiraling TE bundles in interfamilial grafts was discussed., Competing Interests: The authors declare there are no competing interests., (©2022 Wu et al.)

The symplastic tracer 5(6)-carboxyfluorescein diacetate (CFDA) has been widely applied in living plants to demonstrate the intercellular connection, phloem transport and vascular patterning. This protocol shows bottom-to-top carboxyfluorescein (CF) movement in the Arabidopsis by using the root-cutting and the hypocotyl-pinching procedure respectively. These two different procedures result in different efficiencies of CF movement: about 91% appearance of CF in the shoots with the hypocotyl-pinching procedure, whereas only about 70% appearance of CF with the root-cutting procedure. The simple change of loading sites, resulting in significant changes in the mobile efficiency of this symplastic dye, suggests CF movement might be subject to the symplastic regulation, most probably by the root-hypocotyl junction.

The reactive oxygen species, generally labeled toxic due to high reactivity without target specificity, are gradually uncovered as signaling molecules involved in a myriad of biological processes. But one important feature of ROS roles in macromolecule movement has not caught attention until recent studies with technique advance and design elegance have shed lights on ROS signaling for intercellular and interorganelle communication. This review begins with the discussions of genetic and chemical studies on the regulation of symplastic dye movement through intercellular tunnels in plants (plasmodesmata), and focuses on the ROS regulatory mechanisms concerning macromolecule movement including small RNA-mediated gene silencing movement and protein shuttling between cells. Given the premise that intercellular tunnels (bridges) in mammalian cells are the key physical structures to sustain intercellular communication, movement of macromolecules and signals is efficiently facilitated by ROS-induced membrane protrusions formation, which is analogously applied to the interorganelle communication in plant cells. Although ROS regulatory differences between plant and mammalian cells exist, the basis for ROS-triggered conduit formation underlies a unifying conservative theme in multicellular organisms. These mechanisms may represent the evolutionary advances that have enabled multicellularity to gain the ability to generate and utilize ROS to govern material exchanges between individual cells in oxygenated environment.

In plants and nematodes, RNAi can spread from cells from which it is initiated to other cells in the organism. The underlying mechanism controlling the mobility of RNAi signals is not known, especially in the case of plants. A genetic screen designed to recover plants impaired in the movement but not the production or effectiveness of the RNAi signal identified RCI3, which encodes a hydrogen peroxide (H2O2)-producing type III peroxidase, as a key regulator of silencing mobility in Arabidopsis thaliana. Silencing initiated in the roots of rci3 plants failed to spread into leaf tissue or floral tissue. Application of exogenous H2O2 reinstated the spread in rci3 plants and accelerated it in wild-type plants. The addition of catalase or MnO2, which breaks down H2O2, slowed the spread of silencing in wild-type plants. We propose that endogenous H2O2, under the control of peroxidases, regulates the spread of gene silencing by altering plasmodesmata permeability through remodelling of local cell wall structure, and may play a role in regulating systemic viral defence.