A guide to plant TPX2-like and WAVE-DAMPENED2-like proteins

Morphological Analyses and QTL Mapping of Mottled Leaf in Zucchini (Cucurbita pepo L.)

The mottled leaf is one of the agronomic traits of zucchini and can be applied as a marker trait in aggregation breeding. However, the genetic mechanism responsible for mottled leaf has yet to be elucidated. In the present study, we used two inbred lines (line '19': silver mottled leaf; line '113': normal leaf) as parents for the physiological and genetic analysis of mottled leaf. The synthesis and net photosynthetic rate of chlorophyll were not significantly affected in the mottled areas of leaves. However, we detected a large space between the palisade parenchyma in the leaf mottle area of line '19', which may have caused the mottled leaf phenotype. Light also plays an important role in the formation of mottled leaf, and receiving light during the early stages of leaf development is a necessary factor. Genetic analysis has previously demonstrated that mottled leaf is a quantitative trait that is controlled by multiple genes. Based on the strategy of quantitative trait locus sequencing (QTL-seq), two QTLs were identified on chromosomes 1 and 17, named CpML1.1 and CpML17.1, respectively. Two major loci were identified using R/qtl software version 1.66 under greenhouse conditions in April 2019 (2019A) and April 2020 (2020A) and under open cultivation conditions in May 2020 (2020M). The major QTL, CpML1.1, was located in a 925.2-kb interval on chromosome 1 and explained 10.51%-24.15% of the phenotypic variation. The CpML17.1 was located in a 719.7-kb interval on chromosome 17 and explained 16.25%-38.68% of the phenotypic variation. Based on gene annotation, gene sequence alignment, and qRT-PCR analysis, the Cp4.1LG01g23790 at the CpML1.1 locus encoding a protein of the TPX2 family (target protein of Xklp2) may be a candidate gene for mottled leaf in zucchini. Our findings may provide a theoretical basis for the formation of mottled leaf and provide a foundation for the fine mapping of genes associated with mottled leaf. Molecular markers closely linked to mottled leaf can be used in molecular-assisted selection for the zucchini mottled leaf breeding.

miRNA-27b-3p/TPX2 Axis Regulates Clear Cell Renal Cell Carcinoma Cell Proliferation, Invasion and Migration

There is a wide variety of cancer cells that can be linked to the presence of TPX2. However, there is not a lot of evidence regarding its role in the development and maintenance of clear cell renal cell carcinoma (ccRCC). In our study, bioinformatics analysis was performed to obtain differentially expressed mRNAs and miR-NAs in ccRCC. Survival curves predicted correlation of TPX2 expression with patient survival. The upstream regulatory miRNA of TPX2 was predicted to be miRNA-27b-3p through database, and dual luciferase assay verified the targeted relationship. qRT-PCR and Western blot were employed for examination of TPX2 mRNA and protein expression in ccRCC cells. Proliferation, invasion, migration and cell cycle were detected by CCK-8, colony formation, wound healing, Transwell, and flow cytometry assays. The results showed that TPX2 showed very high expression in ccRCC, and patients with higher TPX2 expression had shorter relative survival. Low miRNA-27b-3p expression was found in ccRCC. Knockdown of TPX2 or forced expression of miRNA-27b-3p in ccRCC cells inhibited cell proliferation, migration, invasion, and arrested cell division in G0/G1 phase. Dual luciferase reporter presented that miRNA-27b-3p targeted TPX2 to inhibit its expression. Rescue experiments demonstrated that the miRNA-27b-3p/ TPX2 axis affected the biological functions of ccRCC cells. Concurrent overexpression of miRNA-27b-3p and TPX2 inhibited the facilitating effect of TPX2 on ccRCC cell growth. The results revealed novel regulatory mechanisms involved in ccRCC progression, hoping that it may spark an insight for later discovery about the new therapeutic targets for ccRCC.

Microtubule-associated proteins WDL5 and WDL6 play a critical role in pollen tube growth in Arabidopsis thaliana

Morphological response of cells to environment involves concerted rearrangements of microtubules and actin microfilaments. A mutant of WAVE-DAMPENED2-LIKE5 (WDL5), which encodes an ethylene-regulated microtubule-associated protein belonging to the WVD2/WDL family in Arabidopsis thaliana, shows attenuation in the temporal root growth reduction in response to mechanical stress. We found that a T-DNA knockout of WDL6, the closest homolog of WDL5, oppositely shows an enhancement of the response. To know the functional relationship between WDL5 and WDL6, we attempted to generate the double mutant by crosses but failed in isolation. Close examination of gametophytes in plants that are homozygous for one and heterozygous for the other revealed that these plants produce pollen grains with a reduced rate of germination and tube growth. Reciprocal cross experiments of these plants with the wild type confirmed that the double mutation is not inherited paternally. These results suggest a critical and cooperative function of WDL5 and WDL6 in pollen tube growth.

The role of intrinsic disorder in binding of plant microtubule-associated proteins to the cytoskeleton

Microtubules (MTs) represent one of the main components of the eukaryotic cytoskeleton and support numerous critical cellular functions. MTs are in principle tube-like structures that can grow and shrink in a highly dynamic manner; a process largely controlled by microtubule-associated proteins (MAPs). Plant MAPs are a phylogenetically diverse group of proteins that nonetheless share many common biophysical characteristics and often contain large stretches of intrinsic protein disorder. These intrinsically disordered regions are determinants of many MAP-MT interactions, in which structural flexibility enables low-affinity protein-protein interactions that enable a fine-tuned regulation of MT cytoskeleton dynamics. Notably, intrinsic disorder is one of the major obstacles in functional and structural studies of MAPs and represents the principal present-day challenge to decipher how MAPs interact with MTs. Here, we review plant MAPs from an intrinsic protein disorder perspective, by providing a complete and up-to-date summary of all currently known members, and address the current and future challenges in functional and structural characterization of MAPs.

Warmer temperature during asexual reproduction induce methylome, transcriptomic, and lasting phenotypic changes in Fragaria vesca ecotypes

Plants must adapt with increasing speed to global warming to maintain their fitness. One rapid adaptation mechanism is epigenetic memory, which may provide organisms sufficient time to adapt to climate change. We studied how the perennial Fragaria vesca adapted to warmer temperatures (28°C vs. 18°C) over three asexual generations. Differences in flowering time, stolon number, and petiole length were induced by warmer temperature in one or more ecotypes after three asexual generations and persisted in a common garden environment. Induced methylome changes differed between the four ecotypes from Norway, Iceland, Italy, and Spain, but shared methylome responses were also identified. Most differentially methylated regions (DMRs) occurred in the CHG context, and most CHG and CHH DMRs were hypermethylated at the warmer temperature. In eight CHG DMR peaks, a highly similar methylation pattern could be observed between ecotypes. On average, 13% of the differentially methylated genes between ecotypes also showed a temperature-induced change in gene expression. We observed ecotype-specific methylation and expression patterns for genes related to gibberellin metabolism, flowering time, and epigenetic mechanisms. Furthermore, we observed a negative correlation with gene expression when repetitive elements were found near (±2 kb) or inside genes. In conclusion, lasting phenotypic changes indicative of an epigenetic memory were induced by warmer temperature and were accompanied by changes in DNA methylation patterns. Both shared methylation patterns and transcriptome differences between F. vesca accessions were observed, indicating that DNA methylation may be involved in both general and ecotype-specific phenotypic variation.

HY5 inhibits lateral root initiation in Arabidopsis through negative regulation of the microtubule-stabilizing protein TPXL5

Tight control of lateral root (LR) initiation is vital for root system architecture and function. Regulation of cortical microtubule reorganization is involved in the asymmetric radial expansion of founder cells during LR initiation in Arabidopsis (Arabidopsis thaliana). However, critical genetic evidence on the role of microtubules in LR initiation is lacking and the mechanisms underlying this regulation are poorly understood. Here, we found that the previously uncharacterized microtubule-stabilizing protein TPX2-LIKE5 (TPXL5) participates in LR initiation, which is finely regulated by the transcription factor ELONGATED HYPOCOTYL5 (HY5). In tpxl5 mutants, LR density was decreased and more LR primordia (LRPs) remained in stage I, indicating delayed LR initiation. In particular, the cell width in the peripheral domain of LR founder cells after the first asymmetric cell division was larger in tpxl5 mutants than in the wild-type. Consistently, ordered transverse cortical microtubule arrays were not well generated in tpxl5 mutants. In addition, HY5 directly targeted the promoter of TPXL5 and downregulated TPXL5 expression. The hy5 mutant exhibited higher LR density and fewer stage I LRPs, indicating accelerated LR initiation. Such phenotypes were partially suppressed by TPXL5 knockout. Taken together, our data provide genetic evidence supporting the notion that cortical microtubules are essential for LR initiation and unravel a molecular mechanism underlying HY5 regulation of TPXL5-mediated microtubule reorganization and cell remodeling during LR initiation.

Genome-wide analysis of TPX2 gene family in Populus trichocarpa and its specific response genes under various abiotic stresses

Microtubules are essential for regulating cell morphogenesis, plant growth, and the response of plants to abiotic stresses. TPX2 proteins are the main players determining the spatiotemporally dynamic nature of the MTs. However, how TPX2 members respond to abiotic stresses in poplar remains largely unknown. Herein, 19 TPX2 family members were identified from the poplar genome and analyzed the structural characteristics as well as gene expression patterns. All TPX2 members had the conserved structural characteristics, but exhibited different expression profiles in different tissues, indicating their varying roles during plant growth. Additionally, several light, hormone, and abiotic stress responsive cis-acting regulatory elements were detected on the promoters of PtTPX2 genes. Furthermore, expression analysis in various tissues of Populus trichocarpa showed that the PtTPX2 genes responded differently to heat, drought and salt stress. In summary, these results provide a comprehensive analysis for the TPX2 gene family in poplar and an effective contribution to revealing the mechanisms of PtTPX2 in the regulatory network of abiotic stress.

AUR1 and its pals: orchestration of intracellular rhizobia infection in legume for nitrogen fixation

We highlight the newly emerged regulatory role of a mitotic kinase AUR1, its activator, and its microtubule-associated proteins (MAPs) in infection thread formation for root nodule symbiosis.

Cotton microtubule-associated protein GhMAP20L5 mediates fiber elongation through the interaction with the tubulin GhTUB13

Targeting proteins for Xklp2 (TPX2s) comprise a class of MAPs that are essential for plant growth and development by regulating the dynamic changes of microtubules (MTs) and proper formation of cytoskeleton. However, the function of TPX2 proteins in cotton fiber development remains poorly understood. Here, we identified the function of a fiber elongation-specific TPX2 protein, GhMAP20L5, in cotton. Suppressed GhMAP20L5 gene expression in cotton (GhMAP20L5i) significantly reduced fiber elongation rate, fiber length and lint percentage. GhMAP20L5i fibers had thinner and looser secondary cell walls (SCW), and incompact helix twists. GhMAP20L5 specifically interacted with the tubulin GhTUB13 on the cytoskeleton. Gene coexpression analysis showed that GhMAP20L5 involved in multiple pathways related to cytoskeleton establishment and fiber cell wall formation and affected cellulase genes expressions. In summary, our results revealed that GhMAP20L5 is important for fiber development by regulating cytoskeleton establishment and the cellulose deposition in cotton.

Intracellular infection by symbiotic bacteria requires the mitotic kinase AURORA1

The subcellular events occurring in cells of legume plants as they form transcellular symbiotic-infection structures have been compared with those occurring in premitotic cells. Here, we demonstrate that Aurora kinase 1 (AUR1), a highly conserved mitotic regulator, is required for intracellular infection by rhizobia in Medicago truncatula. AUR1 interacts with microtubule-associated proteins of the TPXL and MAP65 families, which, respectively, activate and are phosphorylated by AUR1, and localizes with them within preinfection structures. MYB3R1, a rhizobia-induced mitotic transcription factor, directly regulates AUR1 through two closely spaced, mitosis-specific activator cis elements. Our data are consistent with a model in which the MYB3R1-AUR1 regulatory module serves to properly orient preinfection structures to direct the transcellular deposition of cell wall material for the growing infection thread, analogous to its role in cell plate formation. Our findings indicate that the eukaryotically conserved MYB3R1-TPXL-AUR1-MAP65 mitotic module was conscripted to support endosymbiotic infection in legumes.