The universal bundling activity of AtVLN4 in diffusely growing cells

GhVLN4 is involved in multiple stress responses and required for resistance to Verticillium wilt

As structural and signaling platform in plant cell, the actin cytoskeleton is regulated by diverse actin binding proteins (ABPs). Villins are one type of major ABPs responsible for microfilament bundling, which have proved to play important roles in plant growth and development. However, the function of villins in stress tolerance is poorly understood. Here, we report the function of cotton GhVLN4 in Verticillium wilt resistance and abiotic stress tolerance. The expression of GhVLN4 was up-regulated by gibberellin, ethylene, ABA, salicylic acid, jasmonate, NaCl, PEG, and Verticillium dahliae treatment, suggesting the involvement of GhVLN4 in multiple stress and hormone responses and signaling. Virus-induced gene silencing GhVLN4 made cotton more susceptible to V. dahliae characterized by the preferential colonization and rapid growth of the fungus in both phloem and xylem of the infected stems. Arabidopsis overexpressing GhVLN4 exhibited higher resistance to V. dahliae, salt and drought than the wild-type plants. The enhanced resistance to V. dahliae is likely related to the upregulated components in SA signaling pathway; the improved tolerance to salt and drought is characterized by upregulation of the components both in ABA- related and ABA-independent signal pathways, along with altered stomatal aperture under drought. Our findings demonstrate that GhVLN4 may play important roles in regulating plant tolerance to both biotic and abiotic stresses.

Gel-free/label-free proteomic analysis of root tip of soybean over time under flooding and drought stresses

Growth in the early stage of soybean is markedly inhibited under flooding and drought stresses. To explore the responsive mechanisms of soybean, temporal protein profiles of root tip under flooding and drought stresses were analyzed using gel-free/label-free proteomic technique. Root tip was analyzed because it was the most sensitive organ against flooding, and it was beneficial to root penetration under drought. UDP glucose: glycoprotein glucosyltransferase was decreased and increased in soybean root under flooding and drought, respectively. Temporal protein profiles indicated that fermentation and protein synthesis/degradation were essential in root tip under flooding and drought, respectively. In silico protein-protein interaction analysis revealed that the inductive and suppressive interactions between S-adenosylmethionine synthetase family protein and B-S glucosidase 44 under flooding and drought, respectively, which are related to carbohydrate metabolism. Furthermore, biotin/lipoyl attachment domain containing protein and Class II aminoacyl tRNA/biotin synthetases superfamily protein were repressed in the root tip during time-course stresses. These results suggest that biotin and biotinylation might be involved in energy management to cope with flooding and drought in early stage of soybean-root tip.

Plant villins: versatile actin regulatory proteins

Regulation of actin dynamics is a central theme in cell biology that is important for different aspects of cell physiology. Villin, a member of the villin/gelsolin/fragmin superfamily of proteins, is an important regulator of actin. Villins contain six gelsolin homology domains (G1-G6) and an extra headpiece domain. In contrast to their mammalian counterparts, plant villins are expressed widely, implying that plant villins play a more general role in regulating actin dynamics. Some plant villins have a defined role in modifying actin dynamics in the pollen tube; most of their in vivo activities remain to be ascertained. Recently, our understanding of the functions and mechanisms of action for plant villins has progressed rapidly, primarily due to the advent of Arabidopsis thaliana genetic approaches and imaging capabilities that can visualize actin dynamics at the single filament level in vitro and in living plant cells. In this review, we focus on discussing the biochemical activities and modes of regulation of plant villins. Here, we present current understanding of the functions of plant villins. Finally, we highlight some of the key unanswered questions regarding the functions and regulation of plant villins for future research.

Control of the actin cytoskeleton in root hair development

The development of root hair includes four stages: bulge site selection, bulge formation, tip growth, and maturation. The actin cytoskeleton is involved in all of these stages and is organized into distinct arrangements in the different stages. In addition to the actin configuration, actin isoforms also play distinct roles in the different stages. The actin cytoskeleton is regulated by actin-binding proteins, such as formin, Arp2/3 complex, profilin, actin depolymerizing factor, and villin. Some upstream signals, i.e. calcium, phospholipids, and small GTPase regulate the activity of these actin-binding proteins to produce the proper actin configuration. We constructed a working model on how the actin cytoskeleton is controlled by actin-binding proteins and upstream signaling in root hair development based on the current literature: at the tip of hairs, actin polymerization appears to be facilitated by Arp2/3 complex that is activated by small GTPase, and profilin that is regulated by phosphatidylinositol 4,5-bisphosphate. Meanwhile, actin depolymerization and turnover are likely mediated by villin and actin depolymerizing factor, which are stimulated by calcium. At the shank, actin cables are produced by formin and villin. Under the complicated interaction, the actin cytoskeleton is controlled spatially and temporally during root hair development.