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Summary: Grain notching is a common deformation that decreases rice (Oryza sativa) quality; however, the underlying molecular basis causing grain notching remains unclear.We report mechanisms underlying grain notching in Small and notched grain (Sng) mutants, which contained an arginine to histidine substitution at amino acid position 422 (R422H) of the α‐tubulin protein OsTUBA3. The R422H mutation decreased cell length and increased cell width/height of glumes and caryopses, but led to elongated caryopses compressed within shortened glumes, thus giving rise to notched and small grains. Glume and caryopsis cells had different dimensional orientations relative to the directions of organ elongation. Thus, the abnormal cell expansion induced in glumes and caryopses by the R422H mutation had different effects on elongation of these organs.The R422H mutation in OsTUBA3 compromised β‐tubulin binding and led to formation of defective heterodimers. This in turn affected tubulin incorporation and microtubule (MT) nucleation and regrowth, consequently leading to MT instability and reducing the transverse orientation. The defective MT dynamics affected cell expansion and shape, causing different alterations in glume and caryopsis dimensions and resulting in grain notching.These data indicate that Arg422 in OsTUBA3 is crucial for MT dynamics and that substitution with His causes grain notching, reducing grain quality and yield. These findings offer valuable insights into the molecular regulation underlying grain development in rice. [ABSTRACT FROM AUTHOR]

As the stimulus-responsive mediator of actin dynamics, actin-depolymerizing factor (ADF)/cofilin is subject to tight regulation. It is well known that kinase-mediated phosphorylation inactivates ADF/cofilin. Here, however, we found that the activity of Arabidopsis ADF7 is enhanced by CDPK16-mediated phosphorylation. We found that CDPK16 interacts with ADF7 both in vitro and in vivo, and it enhances ADF7-mediated actin depolymerization and severing in vitro in a calcium-dependent manner. Accordingly, the rate of actin turnover is reduced in cdpk16 pollen and the amount of actin filaments increases significantly at the tip of cdpk16 pollen tubes. CDPK16 phosphorylates ADF7 at Serine128 both in vitro and in vivo, and the phospho-mimetic mutant ADF7S128D has enhanced actin-depolymerizing activity compared to ADF7. Strikingly, we found that failure in the phosphorylation of ADF7 at Ser128 impairs its function in promoting actin turnover in vivo, which suggests that this phospho-regulation mechanism is biologically significant. Thus, we reveal that CDPK16-mediated phosphorylation up-regulates ADF7 to promote actin turnover in pollen. As the stimulus-responsive mediator of actin dynamics, ADF/cofilin is tightly regulated. This study shows that the actin depolymerization and severing activity of Arabidopsis ADF7 is enhanced by CDPK16-mediated phosphorylation at Ser128 to promote actin turnover in pollen. [ABSTRACT FROM AUTHOR]

SUMMARY: ADF/cofilin is a central regulator of actin dynamics. We previously demonstrated that two closely related Arabidopsis class IIa ADF isovariants, ADF7 and ADF10, are involved in the enhancement of actin turnover in pollen, but whether they have distinct functions remains unknown. Here, we further demonstrate that they exhibit distinct functions in regulating actin turnover both in vitro and in vivo. We found that ADF7 binds to ADP‐G‐actin with lower affinity, and severs and depolymerizes actin filaments less efficiently in vitro than ADF10. Accordingly, in pollen grains, ADF7 more extensively decorates actin filaments and is less freely distributed in the cytoplasm compared to ADF10. We further demonstrate that ADF7 and ADF10 show distinct intracellular localizations during pollen germination, and they have non‐equivalent functions in promoting actin turnover in pollen. We thus propose that cooperation and labor division of ADF7 and ADF10 enable pollen cells to achieve exquisite control of the turnover of different actin structures to meet different cellular needs. Significance Statement: ADF/cofilin is a central regulator of actin dynamics. We here demonstrate that two closely related Arabidopsis ADF isovariants play non‐equivalent roles in enhancing actin turnover in pollen, which provides insights into functional specification of ADF gene family in plants. Our findings also provide insights into the mechanism regulating actin turnover in pollen. [ABSTRACT FROM AUTHOR]

Self-incompatibility (SI) prevents inbreeding through specific recognition and rejection of incompatible pollen. In incompatible Papaver rhoeas pollen, SI triggers a [Ca.sup.2+] signaling cascade, resulting in the inhibition of tip growth, actin depolymerization, and programmed cell death (PCD). We investigated whether actin dynamics were implicated in regulating PCD. Using the actin-stabilizing and depolymerizing drugs jasplakinolide (Jasp) and latrunculin B, we demonstrate that changes in actin filament levels or dynamics play a functional role in initiating PCD in P. rhoeas pollen, triggering a caspase-3--like activity. Significantly, SI-induced PCD in incompatible pollen was alleviated by pretreatment with Jasp. This represents the first account of a specific causal link between actin polymerization status and initiation of PCD in a plant cell and significantly advances our understanding of the mechanisms involved in SI.

Cell-to-cell communication in plants is mediated by plasmodesmata (PD) whose permeability is tightly regulated during plant growth and development. The actin cytoskeleton has been implicated in regulating the permeability of PD, but the underlying mechanism remains largely unknown. Recent characterization of PD-localized formin proteins has shed light on the role and mechanism of action of actin in regulating PD-mediated intercellular trafficking. In this mini-review article, we will describe the progress in this area. [ABSTRACT FROM AUTHOR]

Tight regulation of gene transcription and mRNA splicing is essential for plant growth and development. Here we demonstrate that a plant-specific protein, EMBRYO DEFECTIVE 1579 (EMB1579), controls multiple growth and developmental processes in Arabidopsis. We demonstrate that EMB1579 forms liquid-like condensates both in vitro and in vivo, and the formation of normal-sized EMB1579 condensates is crucial for its cellular functions. We found that some chromosomal and RNA-related proteins interact with EMB1579 compartments, and loss of function of EMB1579 affects global gene transcription and mRNA splicing. Using floral transition as a physiological process, we demonstrate that EMB1579 is involved in FLOWERING LOCUS C (FLC)-mediated repression of flowering. Interestingly, we found that EMB1579 physically interacts with a homologue of Drosophila nucleosome remodeling factor 55-kDa (p55) called MULTIPLE SUPPRESSOR OF IRA 4 (MSI4), which has been implicated in repressing the expression of FLC by forming a complex with DNA Damage Binding Protein 1 (DDB1) and Cullin 4 (CUL4). This complex, named CUL4-DDB1MSI4, physically associates with a CURLY LEAF (CLF)-containing Polycomb Repressive Complex 2 (CLF-PRC2). We further demonstrate that EMB1579 interacts with CUL4 and DDB1, and EMB1579 condensates can recruit and condense MSI4 and DDB1. Furthermore, emb1579 phenocopies msi4 in terms of the level of H3K27 trimethylation on FLC. This allows us to propose that EMB1579 condensates recruit and condense CUL4-DDB1MSI4 complex, which facilitates the interaction of CUL4-DDB1MSI4 with CLF-PRC2 and promotes the role of CLF-PRC2 in establishing and/or maintaining the level of H3K27 trimethylation on FLC. Thus, we report a new mechanism for regulating plant gene transcription, mRNA splicing, and growth and development. This study reveals that a plant-specific protein, EMB1579, controls multiple growth and developmental processes in Arabidopsis thaliana by regulating gene transcription and mRNA splicing through the formation of liquid-like droplets via liquid-liquid phase separation. [ABSTRACT FROM AUTHOR]

Actin filament, also known as microfilament, is one of two major cytoskeletal elements in plants and plays important roles in various biological processes. Like in animal cells, actin filaments have been thought to participate in autophagy in plants. However, surprisingly, in this study we found that actin filaments are dispensable for the occurrence of autophagy in plants. Disruption of actin filaments by short term treatment with actin polymerization inhibitors, cytochalasin D and latrunculin B, or transient overexpression of Profilin 3 in Nicotiana benthamiana had no effect on basal autophagy as well as the upregulation of nocturnal autophagy and salt stress-induced autophagy. Furthermore, anti-microfilament drug treatment affected neither basal nor salt stress-induced autophagy in Arabidopsis. In addition, prolonged perturbation of actin filaments by silencing Actin7 or 24-h treatment with microfilament-disrupting agents in N. benthamiana caused endoplasmic reticulum (ER) disorganization and subsequent degradation via autophagy involving ATG2, 3, 5, 6 and 7. Our findings reveal that, unlike mammalian cells, actin filaments are unnecessary for bulk autophagy in plants. Abbreviations: ATG: autophagy-related; CD: cytochalasin D; Cvt pathway: cytoplasm to vacuole targeting pathway; DMSO: dimethyl sulfoxide; ER: endoplasmic reticulum; LatB: latrunculin B; Nb: Nicotiana benthamiana; PAS: phagophore assembly site; PRF3: Profilin 3; RER: rough ER; SER: smooth ER; TEM: transmission electron microscopy; TRV: Tobacco rattle virus; VIGS: virus-induced gene silencing; wpi: weeks post-agroinfiltration [ABSTRACT FROM AUTHOR]

The luminescence properties of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with different quantum-well (QW) thicknesses were investigated. It is found that with decreasing the QW thicknesses, the integrated intensities of the photoluminescence (PL) and electroluminescence (EL) peaks demonstrate a contrary changing trend. The PL results show that the luminescence efficiency is improved by using thinner QWs. However, in the EL process, such a positive effect is counteracted by the low carrier injection efficiency in the thin QW LEDs, and consequently leads to a lower light output. Based on our experimental results, it is inferred that the tunneling leakage current associated with dislocations should be responsible for the low carrier-injection efficiency and the observed weaker EL integrated intensity of the LEDs with thin QWs. [ABSTRACT FROM AUTHOR]

An advanced three-dimensional electrothermal-coupled simulation model basing on finite-element method numerical simulation is developed to study the electrical and thermal properties of chip-level high-power GaN-based light-emitting diodes (LEDs). The current spreading, heat generation, and transfer in the device are comprehensively considered in this model. The current-spreading effect of the transparent current-spreading layer and the thermal performance of LEDs with interdigitated-electrodes are investigated. The simulation results prove that the temperature distribution in the active layer is strongly affected by the electrode pattern. The obvious heat accumulation in LEDs with conventional interdigitated-electrode patterns can be seen both in the simulated results and the infrared measured results. The heat transfer efficiency can be improved by using a symmetry electrode pattern design. The thermal management of the bump configurations in flip-chip LEDs is also studied. A more reasonable and thermal effective bump configuration is presented, and the simulated results show that a lower average temperature and more uniform heat distribution in the chips can be obtained. [ABSTRACT FROM AUTHOR]