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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. Nuclear movement in growing Arabidopsis root hairs involves both actin filaments and microtubules

   https://doi.org/10.1093/jxb/erac207  

   Brueggeman, Justin M. ; Windham, Ian A. ; Nebenführ, Andreas ; Geitmann, ed., Anja ( May 2022 , Journal of Experimental Botany)

   Nuclear migration during growth and development is a conserved phenomenon among many eukaryotic species. In Arabidopsis, movement of the nucleus is important for root hair growth, but the detailed mechanism behind this movement is not well known. Previous studies in different cell types have reported that the myosin XI-I motor protein is responsible for this nuclear movement by attaching to the nuclear transmembrane protein complex WIT1/WIT2. Here, we analyzed nuclear movement in growing root hairs of wild-type, myosin xi-i, and wit1 wit2 Arabidopsis lines in the presence of actin and microtubule-disrupting inhibitors to determine the individual effects of actin filaments and microtubules on nuclear movement. We discovered that forward nuclear movement during root hair growth can occur in the absence of myosin XI-I, suggesting the presence of an alternative actin-based mechanism that mediates rapid nuclear displacements. By quantifying nuclear movements with high temporal resolution during the initial phase of inhibitor treatment, we determined that microtubules work to dampen erratic nuclear movements during root hair growth. We also observed microtubule-dependent backwards nuclear movement when actin filaments were impaired in the absence of myosin XI-I, indicating the presence of complex interactions between the cytoskeletal arrays during nuclear movements in growing root hairs.

    

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3. VPS45 is required for both diffuse and tip growth of Arabidopsis thaliana cells

   https://doi.org/10.3389/fpls.2023.1120307  

   Mugume, Yosia ; Roy, Rahul ; Agbemafle, William ; Shepard, Gabriella N. ; Vue, Yee ; Bassham, Diane C. ( February 2023 , Frontiers in Plant Science)

   VPS45 belongs to the Sec1/Munc18 family of proteins, which interact with and regulate Qa-SNARE function during membrane fusion. We have shown previously thatArabidopsis thalianaVPS45 interacts with the SYP61/SYP41/VTI12 SNARE complex, which locates on thetrans-Golgi network (TGN). It is required for SYP41 stability, and it functions in cargo trafficking to the vacuole and in cell expansion. It is also required for correct auxin distribution during gravitropism and lateral root growth.

   Asvps45knockout mutation is lethal in Arabidopsis, we identified a mutant,vps45-3, with a point mutation in theVPS45gene causing a serine 284-to-phenylalanine substitution. The VPS45-3 protein is stable and maintains interaction with SYP61 and SYP41. However,vps45-3plants display severe growth defects with significantly reduced organ and cell size, similar tovps45RNAi transgenic lines that have reduced VPS45 protein levels. Root hair and pollen tube elongation, both processes of tip growth, are highly compromised invps45-3. Mutant root hairs are shorter and thicker than those of wild-type plants, and are wavy. These root hairs have vacuolar defects, containing many small vacuoles, compared with WT root hairs with a single large vacuole occupying much of the cell volume. Pollen tubes were also significantly shorter invps45-3compared to WT.

   We thus show that VPS45 is essential for proper tip growth and propose that the observed vacuolar defects lead to loss of the turgor pressure needed for tip growth.

    

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4. Genome wide association analysis of root hair traits in rice reveals novel genomic regions controlling epidermal cell differentiation

   https://doi.org/10.1186/s12870-022-04026-5  

   Hanlon, Meredith T. ; Vejchasarn, Phanchita ; Fonta, Jenna E. ; Schneider, Hannah M. ; McCouch, Susan R. ; Brown, Kathleen M. ( January 2023 , BMC Plant Biology)

   Genome wide association (GWA) studies demonstrate linkages between genetic variants and traits of interest. Here, we tested associations between single nucleotide polymorphisms (SNPs) in rice (Oryza sativa) and two root hair traits, root hair length (RHL) and root hair density (RHD). Root hairs are outgrowths of single cells on the root epidermis that aid in nutrient and water acquisition and have also served as a model system to study cell differentiation and tip growth. Using lines from the Rice Diversity Panel-1, we explored the diversity of root hair length and density across four subpopulations of rice (aus,indica,temperate japonica, andtropical japonica). GWA analysis was completed using the high-density rice array (HDRA) and the rice reference panel (RICE-RP) SNP sets.

   We identified 18 genomic regions related to root hair traits, 14 of which related to RHD and four to RHL. No genomic regions were significantly associated with both traits. Two regions overlapped with previously identified quantitative trait loci (QTL) associated with root hair density in rice. We identified candidate genes in these regions and present those with previously published expression data relevant to root hair development. We re-phenotyped a subset of lines with extreme RHD phenotypes and found that the variation in RHD was due to differences in cell differentiation, not cell size, indicating genes in an associated genomic region may influence root hair cell fate. The candidate genes that we identified showed little overlap with previously characterized genes in rice andArabidopsis.

   Root hair length and density are quantitative traits with complex and independent genetic control in rice. The genomic regions described here could be used as the basis for QTL development and further analysis of the genetic control of root hair length and density. We present a list of candidate genes involved in root hair formation and growth in rice, many of which have not been previously identified as having a relation to root hair growth. Since little is known about root hair growth in grasses, these provide a guide for further research and crop improvement.

    

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5. Tip Growth

   https://doi.org/10.1002/9780470015902.a0023746  

   Gilroy, Simon ; Swanson, Sarah J ( April 2017 , Encyclopedia of life sciences)

   Pollen tubes and root hairs grow by a highly focused deposition of new wall and membrane materials at their growing apex. Comparison of the machinery that localises such growth between these cell types has revealed common components, providing important insight into how plant cells control cell expansion. Such elements include the small GTPases (e.g. ROPs and RABs), gradients and intricate spatial patterning in the fluxes of ions (e.g. Ca2+ and H+) and partitioning of membrane lipids (such as the phosphoinositides). These regulators are coupled to focused action of the secretory machinery (e.g. the exocyst) and cytoskeletal dynamics, with integral roles emerging for actin, tubulin and their associated motor proteins. These components form an integrated regulatory network that imposes robust spatial localisation of the growth machinery and so supports the production of an elongating tube-like growth form where cell expansion is limited to the very apex, that is, tip growth. 

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