CRK5 Protein Kinase Contributes to the Progression of Embryogenesis of Arabidopsis thaliana

Agrobacterium Transformation of Tea Plants (Camellia sinensis (L.) KUNTZE): A Small Experiment with Great Prospects

Tea has historically been one of the most popular beverages, and it is currently an economically significant crop cultivated in over 50 countries. The Northwestern Caucasus is one of the northernmost regions for industrial tea cultivation worldwide. The domestication of the tea plant in this region took approximately 150 years, during which plantations spreading from the Ozurgeti region in northern Georgia to the southern city of Maykop in Russia. Consequently, tea plantations in the Northern Caucasus can serve as a source of unique genotypes with exceptional cold tolerance. Tea plants are known to be recalcitrant to Agrobacterium-mediated transfection. Research into optimal transfection and regeneration methodologies, as well as the identification of tea varieties with enhanced transformation efficiency, is an advanced strategy for improving tea plant culture. The aim of this study was to search for the optimal Agrobacterium tumefaciens-mediated transfection protocol for the Kolkhida tea variety. As a result of optimizing the transfection medium with potassium phosphate buffer at the stages of pre-inoculation, inoculation and co-cultivation, the restoration of normal morphology and improvement in the attachment of Agrobacterium cells to the surface of tea explants were observed by scanning electron microscopy. And an effective method of high-efficiency Agrobacteria tumefaciens-mediated transfection of the best local tea cultivar, Kolkhida, was demonstrated for the first time.

Protein phosphorylation: A molecular switch in plant signaling

Protein phosphorylation modification is crucial for signaling transduction in plant development and environmental adaptation. By precisely phosphorylating crucial components in signaling cascades, plants can switch on and off the specific signaling pathways needed for growth or defense. Here, we have summarized recent findings of key phosphorylation events in typical hormone signaling and stress responses. More interestingly, distinct phosphorylation patterns on proteins result in diverse biological functions of these proteins. Thus, we have also highlighted latest findings that show how the different phosphosites of a protein, also named phosphocodes, determine the specificity of downstream signaling in both plant development and stress responses.

Characterization of the PIN Auxin Efflux Carrier Gene Family and Its Expression during Zygotic Embryogenesis in Persea americana

Auxins are responsible for a large part of the plant development process. To exert their action, they must move throughout the plant and from cell to cell, which is why plants have developed complex transport systems for indole-3-acetic acid (IAA). These transporters involve proteins that transport IAA into cells, transporters that move IAA to or from different organelles, mainly the endoplasmic reticulum, and transporters that move IAA out of the cell. This research determined that Persea americana has 12 PIN transporters in its genome. The twelve transporters are expressed during different stages of development in P. americana zygotic embryos. Using different bioinformatics tools, we determined the type of transporter of each of the P. americana PIN proteins and their structure and possible location in the cell. We also predict the potential phosphorylation sites for each of the twelve-PIN proteins. The data show the presence of highly conserved sites for phosphorylation and those sites involved in the interaction with the IAA.

Dynamic GOLVEN-ROOT GROWTH FACTOR 1 INSENSITIVE signaling in the root cap mediates root gravitropism

Throughout the exploration of the soil, roots interact with their environment and adapt to different conditions. Directional root growth is guided by asymmetric molecular patterns but how these become established or are dynamically regulated is poorly understood. Asymmetric gradients of the phytohormone auxin are established during root gravitropism, mainly through directional transport mediated by polarized auxin transporters. Upon gravistimulation, PIN-FORMED2 (PIN2) is differentially distributed and accumulates at the lower root side to facilitate asymmetric auxin transport up to the elongation zone where it inhibits cell elongation. GOLVEN (GLV) peptides function in gravitropism by affecting PIN2 abundance in epidermal cells. In addition, GLV signaling through ROOT GROWTH FACTOR 1 INSENSITIVE (RGI) receptors regulates root apical meristem maintenance. Here, we show that GLV-RGI signaling in these 2 processes in Arabidopsis (Arabidopsis thaliana) can be mapped to different cells in the root tip and that, in the case of gravitropism, it operates mainly in the lateral root cap (LRC) to maintain PIN2 levels at the plasma membrane (PM). Furthermore, we found that GLV signaling upregulates the phosphorylation level of PIN2 in an RGI-dependent manner. In addition, we demonstrated that the RGI5 receptor is asymmetrically distributed in the LRC and accumulates in the lower side of the LRC after gravistimulation. Asymmetric GLV-RGI signaling in the root cap likely accounts for differential PIN2 abundance at the PM to temporarily support auxin transport up to the elongation zone, thereby representing an additional level of control on the asymmetrical auxin flux to mediate differential growth of the root.

Phylogeny, transcriptional profile, and auxin-induced phosphorylation modification characteristics of conserved PIN proteins in Moso bamboo (Phyllostachys edulis)

Auxin polar transport is an important way for auxin to exercise its function, and auxin plays an irreplaceable role in the rapid growth of Moso bamboo. We identified and performed the structural analysis of PIN-FORMED auxin efflux carriers in Moso bamboo and obtained a total of 23 PhePIN genes from five gene subfamilies. We also performed chromosome localization and intra- and inter-species synthesis analysis. Phylogenetic analyses of 216 PIN genes showed that PIN genes are relatively conserved in the evolution of the Bambusoideae and have undergone intra-family segment replication in Moso bamboo. The PIN genes' transcriptional patterns showed that the PIN1 subfamily plays a major regulatory role. PIN genes and auxin biosynthesis maintain a high degree of consistency in spatial and temporal distribution. Phosphoproteomics analysis identified many phosphorylated protein kinases that respond to auxin regulation through autophosphorylation and phosphorylation of PIN proteins. The protein interaction network showed that there is a plant hormone interaction regulatory network with PIN protein as the core. We provide a comprehensive PIN protein analysis that complements the auxin regulatory pathway in Moso bamboo and paves the way for further auxin regulatory studies in bamboo.

Plants in Microgravity: Molecular and Technological Perspectives

Plants are vital components of our ecosystem for a balanced life here on Earth, as a source of both food and oxygen for survival. Recent space exploration has extended the field of plant biology, allowing for future studies on life support farming on distant planets. This exploration will utilize life support technologies for long-term human space flights and settlements. Such longer space missions will depend on the supply of clean air, food, and proper waste management. The ubiquitous force of gravity is known to impact plant growth and development. Despite this, we still have limited knowledge about how plants can sense and adapt to microgravity in space. Thus, the ability of plants to survive in microgravity in space settings becomes an intriguing topic to be investigated in detail. The new knowledge could be applied to provide food for astronaut missions to space and could also teach us more about how plants can adapt to unique environments. Here, we briefly review and discuss the current knowledge about plant gravity-sensing mechanisms and the experimental possibilities to research microgravity-effects on plants either on the Earth or in orbit.

The gibberellic acid derived from the plastidial MEP pathway is involved in the accumulation of Bamboo mosaic virus

A gene upregulated in Nicotiana benthamiana after Bamboo mosaic virus (BaMV) infection was revealed as 1-deoxy-d-xylulose-5-phosphate reductoisomerase (NbDXR). DXR is the key enzyme in the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway that catalyzes the conversion of 1-deoxy-d-xylulose 5-phosphate to 2-C-methyl-d-erythritol-4-phosphate. Knockdown and overexpression of NbDXR followed by BaMV inoculation revealed that NbDXR is involved in BaMV accumulation. Treating leaves with fosmidomycin, an inhibitor of DXR function, reduced BaMV accumulation. Subcellular localization confirmed that DXR is a chloroplast-localized protein by confocal microscopy. Furthermore, knockdown of 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase, one of the enzymes in the MEP pathway, also reduced BaMV accumulation. The accumulation of BaMV increased significantly in protoplasts treated with isopentenyl pyrophosphate. Thus, the metabolites of the MEP pathway could be involved in BaMV infection. To identify the critical components involved in BaMV accumulation, we knocked down the crucial enzyme of isoprenoid synthesis, NbGGPPS11 or NbGGPPS2. Only NbGGPPS2 was involved in BaMV infection. The geranylgeranyl pyrophosphate (GGPP) synthesized by NbGGPPS2 is known for gibberellin synthesis. We confirmed this result by supplying gibberellic acid exogenously on leaves, which increased BaMV accumulation. The de novo synthesis of gibberellic acid could assist BaMV accumulation.

Subcellular trafficking and post-translational modification regulate PIN polarity in plants

Auxin regulates plant growth and tropism responses. As a phytohormone, auxin is transported between its synthesis sites and action sites. Most natural auxin moves between cells via a polar transport system that is mediated by PIN-FORMED (PIN) auxin exporters. The asymmetrically localized PINs usually determine the directionality of intercellular auxin flow. Different internal cues and external stimuli modulate PIN polar distribution and activity at multiple levels, including transcription, protein stability, subcellular trafficking, and post-translational modification, and thereby regulate auxin-distribution-dependent development. Thus, the different regulation levels of PIN polarity constitute a complex network. For example, the post-translational modification of PINs can affect the subcellular trafficking of PINs. In this review, we focus on subcellular trafficking and post-translational modification of PINs to summarize recent progress in understanding PIN polarity.

BABY BOOM regulates early embryo and endosperm development

The zygote is a totipotent structure that develops into an embryo with all of the cells needed to produce an entire plant. The BABY BOOM (BBM) transcription factor induces spontaneous asexual embryo development on plant organs when ectopically expressed. Although BBM is at the top of a transcriptional network that promotes asexual embryo development, little is known about its expression and role during zygotic embryogenesis. Here we show in Arabidopsis that BBM regulates the progression of zygotic embryo development and embryo patterning, and division and cellularization of the filial endosperm. In line with its role as a totipotency factor, ectopic BBM expression in the egg cell is also sufficient to induce haploid embryo development in Arabidopsis and dicot crops.

The BABY BOOM (BBM) AINTEGUMENTA-LIKE (AIL) AP2/ERF domain transcription factor is a major regulator of plant cell totipotency, as it induces asexual embryo formation when ectopically expressed. Surprisingly, only limited information is available on the role of BBM during zygotic embryogenesis. Here we reexamined BBM expression and function in the model plant Arabidopsis thaliana (Arabidopsis) using reporter analysis and newly developed CRISPR mutants. BBM was expressed in the embryo from the zygote stage and also in the maternal (nucellus) and filial (endosperm) seed tissues. Analysis of CRISPR mutant alleles for BBM (bbm-cr) and the redundantly acting AIL gene PLETHORA2 (PLT2) (plt2-cr) uncovered individual roles for these genes in the timing of embryo progression. We also identified redundant roles for BBM and PLT2 in endosperm proliferation and cellularization and the maintenance of zygotic embryo development. Finally, we show that ectopic BBM expression in the egg cell of Arabidopsis and the dicot crops Brassica napus and Solanum lycopersicon is sufficient to bypass the fertilization requirement for embryo development. Together these results highlight roles for BBM and PLT2 in seed development and demonstrate the utility of BBM genes for engineering asexual embryo development in dicot species.

Phosphorylation control of PIN auxin transporters

The directional transport of the phytohormone auxin is required for proper plant development and tropic growth. Auxin cell-to-cell transport gains directionality through the polar distribution of 'canonical' long PIN-FORMED (PIN) auxin efflux carriers. In recent years, AGC kinases, MAP kinases, Ca²⁺/CALMODULIN-DEPENDENT PROTEIN KINASE-RELATED KINASEs and receptor kinases have been implicated in the control of PIN activity, polarity and trafficking. In this review, we summarize the current knowledge in understanding the posttranslational regulation of PINs by these different protein kinase families. The proposed regulation of PINs by AGC kinases after salt stress and by the stress-activated MAP kinases suggest that abiotic and biotic stress factors may modulate auxin transport and thereby plant growth.

Auxin Transporters-A Biochemical View

From embryogenesis to fruit formation, almost every aspect of plant development and differentiation is controlled by the cellular accumulation or depletion of auxin from cells and tissues. The respective auxin maxima and minima are generated by cell-to-cell auxin transport via transporter proteins. Differential auxin accumulation as a result of such transport processes dynamically regulates auxin distribution during differentiation. In this review, we introduce all auxin transporter (families) identified to date and discuss the knowledge on prominent family members, namely, the PIN-FORMED exporters, ATP-binding cassette B (ABCB)-type transporters, and AUX1/LAX importers. We then concentrate on the biochemical features of these transporters and their regulation by posttranslational modifications and interactors.

Reactive Oxygen Species in Plants: From Source to Sink

Reactive oxygen species (ROS, partial reduction or derivatives of free radicals) are highly reactive, dangerous and can cause oxidative cell death. In addition to their role as toxic by-products of aerobic metabolism, ROS play a role in the control and regulation of biological processes such as growth, the cell cycle, programmed cell death, hormone signaling, biotic and abiotic stress reactions and development. ROS always arise in plants as a by-product of several metabolic processes that are located in different cell compartments, or as a result of the inevitable escape of electrons to oxygen from the electron transport activities of chloroplasts, mitochondria and plasma membranes. These reactive species are formed in chloroplasts, mitochondria, plasma membranes, peroxisomes, apoplasts, the endoplasmic reticulum and cell walls. The action of many non-enzymatic and enzymatic antioxidants present in tissues is required for efficient scavenging of ROS generated during various environmental stressors. The current review provides an in-depth look at the fate of ROS in plants, a beneficial role in managing stress and other irregularities. The production sites are also explained with their negative effects. In addition, the biochemical properties and sources of ROS generation, capture systems, the influence of ROS on cell biochemistry and the crosstalk of ROS with other signaling molecules/pathways are discussed.

Molecular Evolution of Calcium Signaling and Transport in Plant Adaptation to Abiotic Stress

Adaptation to unfavorable abiotic stresses is one of the key processes in the evolution of plants. Calcium (Ca2+) signaling is characterized by the spatiotemporal pattern of Ca2+ distribution and the activities of multi-domain proteins in integrating environmental stimuli and cellular responses, which are crucial early events in abiotic stress responses in plants. However, a comprehensive summary and explanation for evolutionary and functional synergies in Ca2+ signaling remains elusive in green plants. We review mechanisms of Ca2+ membrane transporters and intracellular Ca2+ sensors with evolutionary imprinting and structural clues. These may provide molecular and bioinformatics insights for the functional analysis of some non-model species in the evolutionarily important green plant lineages. We summarize the chronological order, spatial location, and characteristics of Ca2+ functional proteins. Furthermore, we highlight the integral functions of calcium-signaling components in various nodes of the Ca2+ signaling pathway through conserved or variant evolutionary processes. These ultimately bridge the Ca2+ cascade reactions into regulatory networks, particularly in the hormonal signaling pathways. In summary, this review provides new perspectives towards a better understanding of the evolution, interaction and integration of Ca2+ signaling components in green plants, which is likely to benefit future research in agriculture, evolutionary biology, ecology and the environment.

HSP90 affects root growth in Arabidopsis by regulating the polar distribution of PIN1

Auxin homeostasis and signaling affect a broad range of developmental processes in plants. The interplay between HSP90 and auxin signaling is channeled through the chaperoning capacity of the HSP90 on the TIR1 auxin receptor. The sophisticated buffering capacity of the HSP90 system through the interaction with diverse signaling protein components drastically shapes genetic circuitries regulating various developmental aspects. However, the elegant networking capacity of HSP90 in the global regulation of auxin response and homeostasis has not been appreciated. Arabidopsis hsp90 mutants were screened for gravity response. Phenotypic analysis of root meristems and cotyledon veins was performed. PIN1 localization in hsp90 mutants was determined. Our results showed that HSP90 affected the asymmetrical distribution of PIN1 in plasma membranes and influenced its expression in prompt cell niches. Depletion of HSP90 distorted polar distribution of auxin, as the acropetal auxin transport was highly affected, leading to impaired root gravitropism and lateral root formation. The essential role of the HSP90 in auxin homeostasis was profoundly evident from early development, as HSP90 depletion affected embryo development and the pattern formation of veins in cotyledons. Our data suggest that the HSP90-mediated distribution of PIN1 modulates auxin distribution and thereby auxin signaling to properly promote plant development.

Temporal Control of Seed Development in Dicots: Molecular Bases, Ecological Impact and Possible Evolutionary Ramifications

In flowering plants, seeds serve as organs of both propagation and dispersal. The developing seed passes through several consecutive stages, following a conserved general outline. The overall time needed for a seed to develop, however, may vary both within and between plant species, and these temporal developmental properties remain poorly understood. In the present paper, we summarize the existing data for seed development alterations in dicot plants. For genetic mutations, the reported cases were grouped in respect of the key processes distorted in the mutant specimens. Similar phenotypes arising from the environmental influence, either biotic or abiotic, were also considered. Based on these data, we suggest several general trends of timing alterations and how respective mechanisms might add to the ecological plasticity of the families considered. We also propose that the developmental timing alterations may be perceived as an evolutionary substrate for heterochronic events. Given the current lack of plausible models describing timing control in plant seeds, the presented suggestions might provide certain insights for future studies in this field.

The AtCRK5 Protein Kinase Is Required to Maintain the ROS NO Balance Affecting the PIN2-Mediated Root Gravitropic Response in Arabidopsis

The Arabidopsis AtCRK5 protein kinase is involved in the establishment of the proper auxin gradient in many developmental processes. Among others, the Atcrk5-1 mutant was reported to exhibit a delayed gravitropic response via compromised PIN2-mediated auxin transport at the root tip. Here, we report that this phenotype correlates with lower superoxide anion (O2•-) and hydrogen peroxide (H2O2) levels but a higher nitric oxide (NO) content in the mutant root tips in comparison to the wild type (AtCol-0). The oxidative stress inducer paraquat (PQ) triggering formation of O2•- (and consequently, H2O2) was able to rescue the gravitropic response of Atcrk5-1 roots. The direct application of H2O2 had the same effect. Under gravistimulation, correct auxin distribution was restored (at least partially) by PQ or H2O2 treatment in the mutant root tips. In agreement, the redistribution of the PIN2 auxin efflux carrier was similar in the gravistimulated PQ-treated mutant and untreated wild type roots. It was also found that PQ-treatment decreased the endogenous NO level at the root tip to normal levels. Furthermore, the mutant phenotype could be reverted by direct manipulation of the endogenous NO level using an NO scavenger (cPTIO). The potential involvement of AtCRK5 protein kinase in the control of auxin-ROS-NO-PIN2-auxin regulatory loop is discussed.

Do Plasmodesmata Play a Prominent Role in Regulation of Auxin-Dependent Genes at Early Stages of Embryogenesis?

Plasmodesmata form intercellular channels which ensure the transport of various molecules during embryogenesis and postembryonic growth. However, high permeability of plasmodesmata may interfere with the establishment of auxin maxima, which are required for cellular patterning and the development of distinct tissues. Therefore, diffusion through plasmodesmata is not always desirable and the symplastic continuum must be broken up to induce or accomplish some developmental processes. Many data show the role of auxin maxima in the regulation of auxin-responsive genes and the establishment of various cellular patterns. However, still little is known whether and how these maxima are formed in the embryo proper before 16-cell stage, that is, when there is still a nonpolar distribution of auxin efflux carriers. In this work, we focused on auxin-dependent regulation of plasmodesmata function, which may provide rapid and transient changes of their permeability, and thus take part in the regulation of gene expression.

Pho-view of Auxin: Reversible Protein Phosphorylation in Auxin Biosynthesis, Transport and Signaling

The phytohormone auxin plays a central role in shaping plant growth and development. With decades of genetic and biochemical studies, numerous core molecular components and their networks, underlying auxin biosynthesis, transport, and signaling, have been identified. Notably, protein phosphorylation, catalyzed by kinases and oppositely hydrolyzed by phosphatases, has been emerging to be a crucial type of post-translational modification, regulating physiological and developmental auxin output at all levels. In this review, we comprehensively discuss earlier and recent advances in our understanding of genetics, biochemistry, and cell biology of the kinases and phosphatases participating in auxin action. We provide insights into the mechanisms by which reversible protein phosphorylation defines developmental auxin responses, discuss current challenges, and provide our perspectives on future directions involving the integration of the control of protein phosphorylation into the molecular auxin network.

Tissue-specific expression pattern of calcium-dependent protein kinases-related kinases (CRKs) in rice

Calcium-dependent protein kinases-related kinases (CDPK-related kinases; CRKs) are Ser/Thr kinases that bind with Ca²⁺/Calmodulin and play crucial roles in signal transduction pathways during plant growth, development, and responses to multiple stresses. In this study, we have studied detailed organ and tissue-specific expression patterns of rice CRK genes. Our organ-specific RT-PCR analyzes show the differential expression pattern of these genes in various organs of rice. Moreover, our RNA-RNA in situ hybridization study in rice stem base containing developing crown root primordia demonstrates that the expression of CRK genes is spatially restricted to the developing crown root primordia, suggesting their putative role in protein phosphorylation-dependent cellular signaling during rice crown root development. Furthermore, organ-specific differentially expression pattern of CRK genes during floral organogenesis further support for the organ-specific cell signaling during organogenesis. Thus, our study provides a developmentally regulated expression pattern of rice CRK genes, though they are broadly expressed and a basic foundation for functional characterizations of CRK gene members to unravel their specific functions during plant growth and development.

The Arabidopsis RLCK VI_A2 Kinase Controls Seedling and Plant Growth in Parallel with Gibberellin

The plant-specific receptor-like cytoplasmic kinases (RLCKs) form a large, poorly characterized family. Members of the RLCK VI_A class of dicots have a unique characteristic: their activity is regulated by Rho-of-plants (ROP) GTPases. The biological function of one of these kinases was investigated using a T-DNA insertion mutant and RNA interference. Loss of RLCK VI_A2 function resulted in restricted cell expansion and seedling growth. Although these phenotypes could be rescued by exogenous gibberellin, the mutant did not exhibit lower levels of active gibberellins nor decreased gibberellin sensitivity. Transcriptome analysis confirmed that gibberellin is not the direct target of the kinase; its absence rather affected the metabolism and signalling of other hormones such as auxin. It is hypothesized that gibberellins and the RLCK VI_A2 kinase act in parallel to regulate cell expansion and plant growth. Gene expression studies also indicated that the kinase might have an overlapping role with the transcription factor circuit (PIF4-BZR1-ARF6) controlling skotomorphogenesis-related hypocotyl/cotyledon elongation. Furthermore, the transcriptomic changes revealed that the loss of RLCK VI_A2 function alters cellular processes that are associated with cell membranes, take place at the cell periphery or in the apoplast, and are related to cellular transport and/or cell wall reorganisation.

Plant Cell and Organism Development

Plants represent a unique and fascinating group of living organisms [...].