The two domains of cotton WLIM1a protein are functionally divergent

Role of Actin Dynamics and GhACTIN1 Gene in Cotton Fiber Development: A Prototypical Cell for Study

Cotton crop is considered valuable for its fiber and seed oil. Cotton fiber is a single-celled outgrowth from the ovule epidermis, and it is a very dynamic cell for study. It has four distinct but overlapping developmental stages: initiation, elongation, secondary cell wall synthesis, and maturation. Among the various qualitative characteristics of cotton fiber, the important ones are the cotton fiber staple length, tensile strength, micronaire values, and fiber maturity. Actin dynamics are known to play an important role in fiber elongation and maturation. The current review gives an insight into the cotton fiber developmental stages, the qualitative traits associated with cotton fiber, and the set of genes involved in regulating these developmental stages and fiber traits. This review also highlights some prospects for how biotechnological approaches can improve cotton fiber quality.

A legume kinesin controls vacuole morphogenesis for rhizobia endosymbiosis

Symbioses between legumes and rhizobia require establishment of the plant-derived symbiosome membrane, which surrounds the rhizobia and accommodates the symbionts by providing an interface for nutrient and signal exchange. The host cytoskeleton and endomembrane trafficking systems play central roles in the formation of a functional symbiotic interface for rhizobia endosymbiosis; however, the underlying mechanisms remain largely unknown. Here we demonstrate that the nodulation-specific kinesin-like calmodulin-binding protein (nKCBP), a plant-specific microtubule-based kinesin motor, controls central vacuole morphogenesis in symbiotic cells in Medicago truncatula. Phylogenetic analysis further indicated that nKCBP duplication occurs solely in legumes of the clade that form symbiosomes. Knockout of nKCBP results in central vacuole deficiency, defective symbiosomes and abolished nitrogen fixation. nKCBP decorates linear particles along microtubules, and crosslinks microtubules with the actin cytoskeleton, to control central vacuole formation by modulating vacuolar vesicle fusion in symbiotic cells. Together, our findings reveal that rhizobia co-opted nKCBP to achieve symbiotic interface formation by regulating cytoskeletal assembly and central vacuole morphogenesis during nodule development.

Silencing of a Cotton Actin-Binding Protein GhWLIM1C Decreases Resistance against Verticillium dahliae Infection

LIM proteins are widely spread in various types of plant cells and play diversely crucial cellular roles through actin cytoskeleton assembly and gene expression regulation. Till now, it has not been clear whether LIM proteins function in plant pathogen defense. In this study, we characterized a LIM protein, GhWLIM1C, in upland cotton (Gossypium hirsutum). We found that GhWLIM1C could bind and bundle the actin cytoskeleton, and it contains two LIM domains (LIM1 and LIM2). Both the two domains could bind directly to the actin filaments. Moreover, the LIM2 domain additionally bundles the actin cytoskeleton, indicating that it possesses a different biochemical activity than LIM1. The expression of GhWLIM1C responds to the infection of the cotton fungal pathogen Verticillium dahliae (V. dahliae). Silencing of GhWLIM1C decreased cotton resistance to V. dahliae. These may be associated with the down regulated plant defense response, including the PR genes expression and ROS accumulation in the infected cotton plants. In all, these results provide new evidence that a plant LIM protein functions in plant pathogen resistance and the assembly of the actin cytoskeleton are closely related to the triggering of the plant defense response.

Genome-wide identification and expression analysis of the plant specific LIM genes in Gossypium arboreum under phytohormone, salt and pathogen stress

Asiatic cotton (Gossypium arboreum) cultivated as ‘desi cotton’ in India, is renowned for its climate resilience and robustness against biotic and abiotic stresses. The genome of G. arboreum is therefore, considered as a valued reserve of information for discovering novel genes or gene functions for trait improvements in the present context of cotton cultivation world-wide. In the present study, we carried out genome-wide analysis of LIM gene family in desi cotton and identified twenty LIM domain proteins (GaLIMs) which include sixteen animals CRP-like GaLIMs and four plant specific GaLIMs with presence (GaDA1) or absence (GaDAR) of UIM (Ubiquitin Interacting Motifs). Among the sixteen CRP-like GaLIMs, eleven had two conventional LIM domains while, five had single LIM domain which was not reported in LIM gene family of the plant species studied, except in Brassica rapa. Phylogenetic analysis of these twenty GaLIM proteins in comparison with LIMs of Arabidopsis, chickpea and poplar categorized them into distinct αLIM1, βLIM1, γLIM2, δLIM2 groups in CRP-like LIMs, and GaDA1 and GaDAR in plant specific LIMs group. Domain analysis had revealed consensus [(C-X₂-C-X₁₇-H-X₂-C)-X₂-(C-X₂-C-X₁₇-C-X₂-H)] and [(C-X₂-C-X₁₇-H-X₂-C)-X₂-(C-X₄-C-X₁₅-C-X₂-H)] being conserved as first and/or second LIM domains of animal CRP-like GaLIMs, respectively. Interestingly, single LIM domain containing GaLIM15 was found to contain unique consensus with longer inter-zinc-motif spacer but shorter second zinc finger motif. All twenty GaLIMs showed variable spatio-temporal expression patterns and accordingly further categorized into distinct groups of αLIM1, βLIM1, γLIM2 δLIM2 and plant specific LIM (DA1/DAR). For the first time, response of GaDA1/DAR under the influence of biotic and abiotic stresses were studied in cotton, involving treatments with phytohormones (Jasmonic acid and Abscisic acid), salt (NaCl) and wilt causing pathogen (Fusarium oxysporum). Expressions patterns of GaDA1/DAR showed variable response and identified GaDA2 as a probable candidate gene for stress tolerance in G. arboreum.

The cotton XLIM protein (GhXLIM6) is required for fiber development via maintaining dynamic F-actin cytoskeleton and modulating cellulose biosynthesis

LIM domain proteins are cysteine-rich proteins, and are often considered as actin bundlers and transcription factors in plants. However, the roles of XLIM proteins in plants (especially in cotton) remain unexplored in detail so far. In this study, we identified a cotton XLIM protein (GhXLIM6) that is preferentially expressed in cotton fiber during whole elongation stage and early secondary cell wall (SCW) synthesis stage. The GhXLIM6-silenced transgenic cotton produces shorter fibers with thinner cell walls, compared with wild-type (WT). GhXLIM6 protein could directly bind F-actin and promote actin polymerization both in vitro and in vivo. It also acts as a transcription factor to suppress GhKNL1 expression through binding the PAL-box element of GhKNL1 promoter, and subsequently regulate the expression of CesA genes related to cellulose biosynthesis and deposition in SCWs of cotton fibers. The cellulose content in fibers of GhXLIM6RNAi cotton is lower than that in WT. Taken together, these data reveal the dual roles of GhXLIM6 in fiber development. On one hand, GhXLIM6 functions in fiber elongation through binding to F-actin to maintain the dynamic F-actin cytoskeleton. On the other hand, GhXLIM6 fine-tunes fiber SCW formation, probably through directly suppressing transcription of GhKNL1 to promote cellulose biosynthesis.

Molecular identification, phylogenomic characterization and expression patterns analysis of the LIM (LIN-11, Isl1 and MEC-3 domains) gene family in pear (Pyrus bretschneideri) reveal its potential role in lignin metabolism

Lignin is the main component of stone cells, which are a key factor in determining pear quality. Therefore, modification of lignin biosynthesis has important implications for regulating stone cell formation. LIMs are involved in plant development, stress response and metabolism. However, there is still a lack of knowledge about the pear LIM family and lignin-related LIMs. To address this problem, we identified 14 LIMs from the pear genome and named them. Phylogenomic and feature domain analysis showed that they were divided into CRP- and DA&DAR-LIM groups and five subclades. LIMs from the genomes of four rosids (Prunus mummer, Prunus persica, Fragaria vesca and Vitis vinifera) were also identified, and microsynteny analysis revealed the most orthologous gene pairs in the cross of pear/grape and pear/mei. The transcript levels of PbLIMs were significantly affected by SA, ABA and MeJA. Spatio-temporal expression analysis showed that PbLIMs of the δLIM2 subfamily were highly expressed in the flowers. Changes in the expression levels of PbWLIM1a and PbWLIM1b during fruit development was consistent with the changes in lignin content. Combining phylogenetic analyses, protein three-dimensional structure determination and sequence alignment analyses, these two genes were suggested as lignin-related PbLIMs. Subcellular localization results showed that PbWLIM1a and PbWLIM1b were located mainly in the chloroplast. This study lays the foundation for revealing the mechanism of LIM-mediated lignin metabolism to regulate stone cell formation.