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1. A temperature-sensitive FERONIA mutant allele that alters root hair growth

   https://doi.org/10.1093/plphys/kiaa051  

   Kim, Daewon; Yang, Jiyuan; Gu, Fangwei; Park, Sungjin; Combs, Jonathon; Adams, Alexander; Mayes, Heather B; Jeon, Su Jeong; Bahk, Jeong Dong; Nielsen, Erik (December 2020, Plant Physiology)

   null (Ed.)

   Abstract In plants, root hairs undergo a highly polarized form of cell expansion called tip-growth, in which cell wall deposition is restricted to the root hair apex. In order to identify essential cellular components that might have been missed in earlier genetic screens, we identified conditional temperature-sensitive (ts) root hair mutants by ethyl methanesulfonate mutagenesis in Arabidopsis thaliana. Here, we describe one of these mutants, feronia-temperature sensitive (fer-ts). Mutant fer-ts seedlings were unaffected at normal temperatures (20°C), but failed to form root hairs at elevated temperatures (30°C). Map based-cloning and whole-genome sequencing revealed that fer-ts resulted from a G41S substitution in the extracellular domain of FERONIA (FER). A functional fluorescent fusion of FER containing the fer-ts mutation localized to plasma membranes, but was subject to enhanced protein turnover at elevated temperatures. While tip-growth was rapidly inhibited by addition of rapid alkalinization factor 1 (RALF1) peptides in both wild-type and fer-ts mutants at normal temperatures, root elongation of fer-ts seedlings was resistant to added RALF1 peptide at elevated temperatures. Additionally, at elevated temperatures fer-ts seedlings displayed altered reactive oxygen species (ROS) accumulation upon auxin treatment and phenocopied constitutive fer mutant responses to a variety of plant hormone treatments. Molecular modeling and sequence comparison with other Catharanthus roseus receptor-like kinase 1L (CrRLK1L) receptor family members revealed that the mutated glycine in fer-ts is highly conserved, but is not located within the recently characterized RALF23 and LORELI-LIKE-GLYCOPROTEIN 2 binding domains, perhaps suggesting that fer-ts phenotypes may not be directly due to loss of binding to RALF1 peptides. 

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2. SPIRRIG is required for BRICK1 stability and salt stress induced root hair developmental plasticity in Arabidopsis

   https://doi.org/10.1007/s44154-024-00190-w  

   Zhang, Chi; Zeng, Jingyu; Xie, Wenjuan; Liu, Chuanseng; Niu, Linyu; Wang, Yanling; Wang, Yali; Shi, Muyang; Shao, Jingxia; Wang, Wenjia; et al (December 2024, Stress Biology)

   Developmental plasticity is critical for plants to adapt to constantly changing environments. Plant root hairs display dramatic plasticity under different environments and therefore play crucial roles in defense against environmental stressors. Here, we report the isolation of an Arabidopsis mutant, salinity over-sensitive mutant 1-1 (som1-1), also exhibiting root hair developmental defects. Map-based cloning and allelic analyses confirmed that som1-1 is a new mutant allele of SPIRRIG (SPI), which encodes a Beige and Chediak Higashi (BEACH) domain-containing protein. SPI has been reported to facilitate actin dependent root hair development by temporally and spatially regulating the expression of BRICK1 (BRK1), a subunit of the SCAR/WAVE actin nucleating promoting complex. Our living cell imaging examinations revealed that salt stress induces an altered actin organization in root hair that mimics those in the spi mutant, implying SPI may respond to salt stress induced root hair plasticity by modulating actin cytoskeleton organization. Furthermore, we found BRK1 is also involved in root hair developmental change under salt stress, and overexpression of BRK1 resulted in root hairs over-sensitive to salt stress as those in spi mutant. Moreover, based on biochemical analyses, we found BRK1 is unstable and SPI mediates BRK1 stability. Functional loss of SPI results in the accumulation of steady-state of BRK1. 

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3. The root hairless mutant buzz in Brachypodium distachyon shows increased nitrate uptake and signaling but does not affect overall nitrogen use efficiency

   https://doi.org/10.1111/tpj.17143  

   Rosas, Miguel_A; Alvarez, José_M; Sanguinet, Karen_A (November 2024, The Plant Journal)

   SUMMARY Root systems are uniquely adapted to fluctuations in external nutrient availability. In response to suboptimal nitrogen conditions, plants adopt a root foraging strategy that favors a deeper and more branched root architecture, enabling them to explore and acquire soil resources. This response is gradually suppressed as nitrogen conditions improve. However, the root hairless mutantbuzzinBrachypodium distachyonshows a constitutive nitrogen‐foraging phenotype with increased root growth and root branching under nitrate‐rich conditions. To investigate how this unique root structure and root hair morphology in thebuzzmutant affects nitrate metabolism, we measured the expression of nitrate‐responsive genes, nitrate uptake and accumulation, nitrate reductase activity, and nitrogen use efficiency. We found that nitrate responses were upregulated by low nitrate conditions inbuzzrelative to wild type and correlated with increased expression of nitrate transport genes. In addition,buzzmutants showed increased nitrate uptake and a higher accumulation of nitrate in shoots. Thebuzzmutant also showed increased nitrate reductase activity in the shoots under low nitrate conditions. However, developmentally mature wild‐type andbuzzplants grown under low nitrate had similar nitrogen use efficiencies. These findings suggest thatBUZZinfluences nitrate signaling and that enhanced responsiveness to nitrate is required inbuzzseedlings to compensate for the lack of root hairs. These data question the importance of root hairs in enhancing nitrate uptake and expand our understanding of how root hairs in grasses affect physiological responses to low nitrate availability. 

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4. Rapid systemic responses of Arabidopsis to waterlogging stress

   https://doi.org/10.1093/plphys/kiad433  

   Peláez-Vico, María Ángeles; Tukuli, Adama; Singh, Pallav; Mendoza-Cózatl, David G; Joshi, Trupti; Mittler, Ron (August 2023, Plant Physiology)

   Abstract Waterlogging stress (WLS) negatively impacts the growth and yield of crops resulting in heavy losses to agricultural production. Previous studies have revealed that WLS induces a systemic response in shoots that is partially dependent on the plant hormones ethylene and abscisic acid. However, the role of rapid cell-to-cell signaling pathways, such as the reactive oxygen species (ROS) and calcium waves, in systemic responses of plants to WLS is unknown at present. Here, we reveal that an abrupt WLS treatment of Arabidopsis (Arabidopsis thaliana) plants growing in peat moss triggers systemic ROS and calcium wave responses and that the WLS-triggered ROS wave response of Arabidopsis is dependent on the ROS-generating RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), calcium-permeable channels GLUTAMATE-LIKE RECEPTOR 3.3 and 3.6 (GLR3.3 and GLR3.6), and aquaporin PLASMA MEMBRANE INTRINSIC PROTEIN 2;1 (PIP2;1) proteins. We further show that WLS is accompanied by a rapid systemic transcriptomic response that is evident as early as 10 min following waterlogging initiation, includes many hypoxia-response transcripts, and is partially dependent on RBOHD. Interestingly, the abrupt WLS of Arabidopsis resulted in the triggering of a rapid hydraulic wave response and the transient opening of stomata on leaves. In addition, it induced in plants a heightened state of tolerance to a subsequent submergence stress. Taken together, our findings reveal that the initiation of WLS in plants is accompanied by rapid systemic physiological and transcriptomic responses that involve the ROS, calcium, and hydraulic waves, as well as the induction of hypoxia acclimation mechanisms in systemic tissues. 

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5. Plasmodesmata-localized proteins and ROS orchestrate light-induced rapid systemic signaling in Arabidopsis

   https://doi.org/10.1126/scisignal.abf0322  

   Fichman, Yosef; Myers, Ronald J.; Grant, DeAna G.; Mittler, Ron (February 2021, Science Signaling)

   null (Ed.)

   Systemic signaling and systemic acquired acclimation (SAA) are key to the survival of plants during episodes of abiotic stress. These processes depend on a continuous chain of cell-to-cell signaling events that extends from the initial tissue that senses the stress (the local tissue) to the entire plant (systemic tissues). Reactive oxygen species (ROS) and Ca 2+ are key signaling molecules thought to be involved in this cell-to-cell mechanism. Here, we report that the systemic response of Arabidopsis thaliana to a local treatment of high light stress, which resulted in local ROS accumulation, required ROS generated by respiratory burst oxidase homolog D (RBOHD). ROS increased cell-to-cell transport and plasmodesmata (PD) pore size in a manner dependent on PD-localized protein 1 (PDLP1) and PDLP5, and this process was required for the propagation of the systemic ROS signals and SAA. Furthermore, aquaporins and several Ca 2+ -permeable channels in the glutamate receptor–like (GLR), mechanosensitive small conductance–like (MSL), and cyclic nucleotide–gated (CNGC) families were involved in this systemic signaling process. However, we determined that these channels were required primarily to amplify the systemic signal in each cell along the path of the systemic ROS wave, as well as to establish local and systemic acclimation. Thus, PD and RBOHD-generated ROS orchestrate light stress–induced rapid cell-to-cell spread of systemic signals in Arabidopsis . 

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