Plasma membrane protein OsMCA1 is involved in regulation of hypo-osmotic shock-induced Ca2+ influx and modulates generation of reactive oxygen species in cultured rice cells

A DUF966 gene family member OsDSR3 positively regulates alkali stress tolerance in rice

Rice growth and production are severely constrained by alkali stress. However, the mechanism underlying the rice tolerance to alkali stress is unclear. OsDSR3, a novel gene from the domains of unknown function 966 (DUF966) family, was identified and characterized for its function in the response of rice to alkali stress. The result of this study clearly showed that alkali stress significantly induced OsDSR3 expression level. Moreover, the expression of OsDSR3 was up-regulated by drought, salt, cold, H2O2 and abscisic acid (ABA), and down-regulated by gibberellic acid (GA3), and 2,4-Dichlorophenoxyacetic acid (2,4-D) treatments. Subcellular localization exhibited that OsDSR3 was detected in the nucleus and membrane. OsDSR3-overexpressing (OsDSR3-OE) plants showed higher tolerance to alkali stress than the wild-type (WT). In contrast, OsDSR3 knockout (OsDSR3-KO) mutants were more vulnerable to alkali stress. The differentially expressed genes (DEGs) among OsDSR3-OE and WT seedlings were mainly enriched in porphyrin and chlorophyll, starch and sucrose, and carotenoid metabolic pathways. Among these DEGs, 26 were identified as potential alkali stress-responsive genes, including several up-regulated genes like OsHAK5, OsGRX23 and OsNIR2. Consistent with the expression profiles of metabolic pathways-related genes, most of the metabolite contents and metabolite synthases activities were improved in OsDSR3-OE lines and decreased in OsDSR3-KO lines compared to WT. This may explain the higher tolerance of OE lines and lower tolerance of KO lines to alkali stress. These findings suggested that OsDSR3 positively regulates rice tolerance to alkali stress, which will help to elucidate the molecular mechanism underlying rice alkali tolerance.

RsRbohD1 Plays a Significant Role in ROS Production during Radish Pithiness Development

Pithiness is one of the physiological diseases of radishes, which is accompanied by the accumulation of reactive oxygen species (ROS) during the sponging of parenchyma tissue in the fleshy roots. A respiratory burst oxidase homolog (Rboh, also known as NADPH oxidase) is a key enzyme that catalyzes the production of ROS in plants. To understand the role of Rboh genes in radish pithiness, herein, 10 RsRboh gene families were identified in the genome of Raphanus sativus using Blastp and Hmmer searching methods and were subjected to basic functional analyses such as phylogenetic tree construction, chromosomal localization, conserved structural domain analysis, and promoter element prediction. The expression profiles of RsRbohs in five stages (Pithiness grade = 0, 1, 2, 3, 4, respectively) of radish pithiness were analyzed. The results showed that 10 RsRbohs expressed different levels during the development of radish pithiness. Except for RsRbohB and RsRbohE, the expression of other members increased and reached the peak at the P2 (Pithiness grade = 2) stage, among which RsRbohD1 showed the highest transcripts. Then, the expression of 40 genes related to RsRbohD1 and pithiness were analyzed. These results can provide a theoretical basis for improving pithiness tolerance in radishes.

iJAZ-based approach to engineer lepidopteran pest resistance in multiple crop species

The fall armyworm (FAW) poses a significant threat to global crop production. Here we showed that overexpression of jasmonate ZIM-domain (JAZ) protein GhJAZ24 confers resistance to cotton bollworm and FAW, while also causing sterility in transgenic cotton by recruiting TOPLESS and histone deacetylase 6. We identified the NGR motif of GhJAZ24 that recognizes and binds the aminopeptidase N receptor, enabling GhJAZ24 to enter cells and disrupt histone deacetylase 3, leading to cell death. To overcome plant sterility associated with GhJAZ24 overexpression, we developed iJAZ (i, induced), an approach involving damage-induced expression and a switch from intracellular to extracellular localization of GhJAZ24. iJAZ transgenic cotton maintained fertility and showed insecticidal activity against cotton bollworm and FAW. In addition, iJAZ transgenic rice, maize and tobacco plants showed insecticidal activity against their lepidopteran pests, resulting in an iJAZ-based approach for generating alternative insecticidal proteins with distinctive mechanisms of action, thus holding immense potential for future crop engineering.

Designing salt stress-resilient crops: Current progress and future challenges

Excess soil salinity affects large regions of land and is a major hindrance to crop production worldwide. Therefore, understanding the molecular mechanisms of plant salt tolerance has scientific importance and practical significance. In recent decades, studies have characterized hundreds of genes associated with plant responses to salt stress in different plant species. These studies have substantially advanced our molecular and genetic understanding of salt tolerance in plants and have introduced an era of molecular design breeding of salt-tolerant crops. This review summarizes our current knowledge of plant salt tolerance, emphasizing advances in elucidating the molecular mechanisms of osmotic stress tolerance, salt-ion transport and compartmentalization, oxidative stress tolerance, alkaline stress tolerance, and the trade-off between growth and salt tolerance. We also examine recent advances in understanding natural variation in the salt tolerance of crops and discuss possible strategies and challenges for designing salt stress-resilient crops. We focus on the model plant Arabidopsis (Arabidopsis thaliana) and the four most-studied crops: rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and soybean (Glycine max).

PHB3 interacts with BRI1 and BAK1 to mediate brassinosteroid signal transduction in Arabidopsis and tomato

Brassinosteroids (BRs) are plant hormones that are essential in plant growth and development. BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and BRI1 ASSOCIATED RECEPTOR KINASE 1 (BAK1), which are located on the plasma membrane, function as co-receptors that accept and transmit BR signals. PROHIBITIN 3 (PHB3) was identified in both BRI1 and BAK1 complexes by affinity purification and LC-MS/MS analysis. Biochemical data showed that BRI1/BAK1 interacted with PHB3 in vitro and in vivo. BRI1/BAK1 phosphorylated PHB3 in vitro. When the Thr-80 amino acid in PHB3 was mutated to Ala, the mutant protein was not phosphorylated by BRI1 and the mutant protein interaction with BRI1 was abolished in the yeast two-hybrid assay. BAK1 did not phosphorylate the mutant protein PHB3T54A . The loss-of-function phb3 mutant showed a weaker BR signal than the wild-type. Genetic analyses revealed that PHB3 is a BRI1/BAK1 downstream substrate that participates in BR signalling. PHB3 has five homozygous in tomato, and we named the closest to AtPHB3 as SlPHB3.1. Biochemical data showed that SlBRI1/SlSERK3A/SlSERK3B interacted with SlPHB3.1 and SlPHB3.3. The CRISPR-Cas9 method generated slphb3.1 mutant led to a BR signal stunted relatively in tomatoes. PHB3 is a new component of the BR signal pathway in both Arabidopsis and tomato.

Knockout of a rice K5.2 gene increases Ca accumulation in the grain

Rice is a staple food for half of the world's population, but it is a poor dietary source of calcium (Ca) due to the low concentration. It is an important issue to boost Ca concentration in this grain to improve Ca deficiency risk, but the mechanisms underlying Ca accumulation are poorly understood. Here, we obtained a rice (Oryza sativa) mutant with high shoot Ca accumulation. The mutant exhibited 26%-53% higher Ca in shoots than did wild-type rice (WT) at different Ca supplies. Ca concentration in the xylem sap was 36% higher in the mutant than in the WT. There was no difference in agronomic traits between the WT and mutant, but the mutant showed 25% higher Ca in the polished grain compared with the WT. Map-based cloning combined with a complementation test revealed that the mutant phenotype was caused by an 18-bp deletion of a gene, OsK5.2, belonging to the Shaker-like K+ channel family. OsK5.2 was highly expressed in the mature region of the roots and its expression in the roots was not affected by Ca levels, but upregulated by low K. Immunostaining showed that OsK5.2 was mainly expressed in the pericycle of the roots. Taken together, our results revealed a novel role for OsK5.2 in Ca translocation in rice, and will be a good target for Ca biofortification in rice.

Understanding the mechanobiology of phytoacoustics through molecular Lens: Mechanisms and future perspectives

BACKGROUND

How plants emit, perceive, and respond to sound vibrations (SVs) is a long-standing question in the field of plant sensory biology. In recent years, there have been numerous studies on how SVs affect plant morphological, physiological, and biochemical traits related to growth and adaptive responses. For instance, under drought SVs navigate plant roots towards water, activate their defence responses against stressors, and increase nectar sugar in response to pollinator SVs. Also, plants emit SVs during stresses which are informative in terms of ecological and adaptive perspective. However, the molecular mechanisms underlying the SV perception and emission in plants remain largely unknown. Therefore, deciphering the complexity of plant-SV interactions and identifying bonafide receptors and signaling players will be game changers overcoming the roadblocks in phytoacoustics.

AIM OF REVIEW

The aim of this review is to provide an overview of recent developments in phytoacoustics. We primarily focuss on SV signal perception and transduction with current challenges and future perspectives.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Timeline breakthroughs in phytoacoustics have constantly shaped our understanding and belief that plants may emit and respond to SVs like other species. However, unlike other plant mechanostimuli, little is known about SV perception and signal transduction. Here, we provide an update on phytoacoustics and its ecological importance. Next, we discuss the role of cell wall receptor-like kinases, mechanosensitive channels, intracellular organelle signaling, and other key players involved in plant-SV receptive pathways that connect them. We also highlight the role of calcium (Ca2+), reactive oxygen species (ROS), hormones, and other emerging signaling molecules in SV signal transduction. Further, we discuss the importance of molecular, biophysical, computational, and live cell imaging tools for decoding the molecular complexity of acoustic signaling in plants. Finally, we summarised the role of SV priming in plants and discuss how SVs could modulate plant defense and growth trade-offs during other stresses.

Calcium signaling-mediated transcriptional reprogramming during abiotic stress response in plants

Calcium (Ca2+) is a second messenger in plants growth and development, as well as in stress responses. The transient elevation in cytosolic Ca2+ concentration have been reported to be involved in plants response to abiotic and biotic stresses. In plants, Ca2+-induced transcriptional changes trigger molecular mechanisms by which plants adapt and respond to environment stresses. The mechanism for transcription regulation by Ca2+ could be either rapid in which Ca2+ signals directly cause the related response through the gene transcript and protein activities, or involved amplification of Ca2+ signals by up-regulation the expression of Ca2+ responsive genes, and then increase the transmission of Ca2+ signals. Ca2+ regulates the expression of genes by directly binding to the transcription factors (TFs), or indirectly through its sensors like calmodulin, calcium-dependent protein kinases (CDPK) and calcineurin B-like protein (CBL). In recent years, significant progress has been made in understanding the role of Ca2+-mediated transcriptional regulation in different processes in plants. In this review, we have provided a comprehensive overview of Ca2+-mediated transcriptional regulation in plants in response to abiotic stresses including nutrition deficiency, temperature stresses (like heat and cold), dehydration stress, osmotic stress, hypoxic, salt stress, acid rain, and heavy metal stress.

Pavement cells distinguish touch from letting go

A micro-cantilever technique applied to individual leaf epidermis cells of intact Arabidopsis thaliana and Nicotiana tabacum synthesizing genetically encoded calcium indicators (R-GECO1 and GCaMP3) revealed that compressive forces induced local calcium peaks that preceded delayed, slowly moving calcium waves. Releasing the force evoked significantly faster calcium waves. Slow waves were also triggered by increased turgor and fast waves by turgor drops in pressure probe tests. The distinct characteristics of the wave types suggest different underlying mechanisms and an ability of plants to distinguish touch from letting go.

ZmCIPK32 positively regulates germination of stressed seeds via gibberellin signal

Calcineurin B-like proteins (CBLs) as specific calcium sensors that interact with CBL-interacting protein kinases (CIPKs) play a key role in the regulation of plant development and abiotic stress tolerance. In this study, we isolated and characterized the CIPK32 gene from Zea mays. ZmCIPK32 showed that it comprised 440 amino acids and a conserved NAF motif responsible for the interaction with CBLs localized in the cytoplasm and cell membrane. The interaction of ZmCIPK32 with ZmCBL1 and ZmCBL9 demonstrated using yeast two-hybrid system and bimolecular fluorescence complementation assay required the presence of the NAF domain. Overexpression of ZmCIPK32 promoted early germination in transgenic Arabidopsis seeds relative to that observed in wild-type (WT) plants under mannitol treatment. In addition, ZmCIPK32-overexpressing plants were insensitive to treatments with exogenous abscisic acid and paclobutrazol (PBZ) at seed germination and early seedling stages. Expression levels of the key genes GA20ox and GA3ox involved in the synthesis of gibberellin (GA) were increased, whereas expression levels of genes involved in the conversion of active GA to inactive forms and GA signaling were reduced in ZmCIPK32-overexpressing plants relative to those in WT plants under mannitol and PBZ treatments. Furthermore, overexpression of ZmCIPK32 increased GA level but decreased abscisic acid level in transgenic lines compared to the respective levels in WT plants under PBZ or mannitol treatments. Our results suggest that ZmCIPK32 positively regulates seed germination under stressed conditions by modulating GA signals.

A receptor-like kinase controls the amplitude of secondary cell wall synthesis in rice

Cell wall expansion is a key element in determining plant morphology and growth, and cell wall integrity changes are relayed to the cell to fine-tune growth responses. Here, we show that variations in the ectodomain of a cell wall-associated receptor-like kinase, WAK10, in temperate Oryza japonica accessions differentially amplify fluctuations in cell wall integrity to control rice stem height. Mutation in the WAK10 gene exhibited increased cell wall thickening in stem sclerenchyma and reduced cell expansion in the stem. Two WAK10 ectodomain variants bound pectic oligosaccharides with different affinities. The pectic oligosaccharide binding regulated WAK10 phosphorylation activity, the amplitude of secondary wall deposition, and ultimately, stem height. Rice population analyses revealed active enrichment of the short-stem WAK10 ectodomain alleles in japonica subspecies during domestication. Our study outlines not only a mechanism for how variations in ligand affinities of a receptor kinase control cell wall biosynthesis and plant growth, but it also provides breeding targets for new semi-dwarf rice cultivars.

Calcium signaling in plant immunity: a spatiotemporally controlled symphony

Calcium ions (Ca²⁺) are prominent intracellular messengers in all eukaryotic cells. Recent studies have emphasized the crucial roles of Ca²⁺ in plant immunity. Here, we review the latest progress on the spatiotemporal control of Ca²⁺ function in plant immunity. We discuss discoveries of how Ca²⁺ influx is triggered upon the activation of immune receptors, how Ca²⁺-permeable channels are activated, how Ca²⁺ signals are decoded inside plant cells, and how these signals are switched off. Despite recent advances, many open questions remain and we highlight the existing toolkit and the new technologies to address the outstanding questions of Ca²⁺ signaling in plant immunity.

Characterization of phosphate transporter genes and the function of SgPT1 involved in phosphate uptake in Stylosanthes guianensis

Phosphorus (P) is one of the principal macronutrients for plant growth and productivity. Although the phosphate (Pi) transporter (PT) of the PHT1 family has been functionally characterized as participating in Pi uptake and transport in plants, information about PT genes in stylo (Stylosanthes guianensis), an important tropical forage legume that exhibits good adaptability to low-P acid soils, is limited. In this study, stylo root growth was found to be stimulated under P deficiency. The responses of PT genes to nutrient deficiencies and their roles in Pi uptake were further investigated in stylo. Four novel PT genes were identified in stylo and designated SgPT2 to SgPT5. Like SgPT1, which had been previously identified, all five SgPT proteins harboured the major facilitator superfamily (MFS) domain. Variations in tissue-specific expression were observed among the SgPT genes, which displayed diverse responses to deficiencies in nitrogen (N), P and potassium (K) in stylo roots. Four of the five SgPTs exhibited high levels of transcriptional responsiveness to P deficiency in roots. Furthermore, SgPT1, a Pi-starvation-induced gene closely related to legume PT homologues that participate in Pi transport, was selected for functional analysis. SgPT1 was localized to the plasma membrane. Analysis of transgenic Arabidopsis showed that overexpression of SgPT1 led to increased Pi accumulation and promoted root growth in Arabidopsis plants. Taken together, the results of this study suggest the involvement of SgPTs in the stylo response to nutrient deprivation. SgPT1 might mediate Pi uptake in stylo, which is beneficial for root growth during P deficiency.

Structure, Function, and Applications of Soybean Calcium Transporters

Glycine max is a calcium-loving crop. The external application of calcium fertilizer is beneficial to the increase of soybean yield. Indeed, calcium is a vital nutrient in plant growth and development. As a core metal ion in signaling transduction, calcium content is maintained in dynamic balance under normal circumstances. Now, eight transporters were found to control the uptake and efflux of calcium. Though these calcium transporters have been identified through genome-wide analysis, only a few of them were functionally verified. Therefore, in this study, we summarized the current knowledge of soybean calcium transporters in structural features, expression characteristics, roles in stress response, and prospects. The above results will be helpful in understanding the function of cellular calcium transport and provide a theoretical basis for elevating soybean yield.

SgNramp1, a plasma membrane-localized transporter, involves in manganese uptake in Stylosanthes guianensis

Transporters belonging to the natural resistance-associated macrophage protein (Nramp) family play important roles in metal uptake and homeostasis. Although Nramp members have been functionally characterized in plants, the role of Nramp in the important tropical forage legume Stylosanthes guianensis (stylo) is largely unknown. This study aimed to determine the responses of Nramp genes to metal stresses and investigate its metal transport activity in stylo. Five SgNramp genes were identified from stylo. Expression analysis showed that SgNramp genes exhibited tissue preferential expressions and diverse responses to metal stresses, especially for manganese (Mn), suggesting the involvement of SgNramps in the response of stylo to metal stresses. Of the five SgNramps, SgNramp1 displayed the highest expression in stylo roots. A close correlation between SgNramp1 expression and root Mn concentration was observed among nine stylo cultivars under Mn limited condition. The higher expression of SgNramp1 was correlated with a high Mn uptake in stylo. Subsequent subcellular localization analysis showed that SgNramp1 was localized to the plasma membrane. Furthermore, heterologous expression of SgNramp1 complemented the phenotype of the Mn uptake-defective yeast (Saccharomyces cerevisiae) mutant Δsmf1. Mn concentration in the yeast cells expressing SgNramp1 was higher than that of the empty vector control, suggesting the transport activity of SgNramp1 for Mn in yeast. Taken together, this study reveals that SgNramp1 is a plasma membrane-localized transporter responsible for Mn uptake in stylo.

Amino acid transporter gene TaATLa1 from Triticum aestivum L. improves growth under nitrogen sufficiency and is down regulated under nitrogen deficiency

TaATLa1 was identified to respond to nitrogen deprivation through transcriptome analysis of wheat seedlings. TaATLa1 specifically transports Gln, Glu, and Asp, and affects the biomass of Arabidopsis and wheat. Nitrogen is an essential macronutrient and plays a crucial role in wheat production. Amino acids, the major form of organic nitrogen, are remobilized by amino acid transporters (AATs) in plants. AATs are commonly described as central components of essential developmental processes and yield formation via taking up and transporting amino acids in plants. However, few studies have reported the detailed biochemical properties and biological functions of these AATs in wheat. In this study, key genes encoding AATs were screened from transcriptome analysis of wheat seedlings treated with normal nitrogen (NN) and nitrogen deprivation (ND). Among them, 21 AATs were down-regulated and eight AATs were up-regulated under ND treatment. Among the homoeologs, TaATLa1.1-3A, TaATLa1.1-3B, and TaATLa1.1-3D (TaATLa1.1-3A, -3B, and -3D), belonging to amino acid transporter-like a (ATLa) subfamily, were significantly down-regulated in response to ND in wheat, and accordingly were selected for functional analyses. The results demonstrated that TaATLa1.1-3A, -3B, and -3D effectively transported glutamine (Gln), glutamate (Glu), and aspartate (Asp) in yeast. Overexpression of TaAILa1.1-3A, -3B, and -3D in Arabidopsis thaliana L. significantly increased amino acid content in leaves, storage protein content in seeds and the plant biomass under NN. Knockdown of TaATLa1.1-3A, -3B, and -3D in wheat seedlings resulted in a significant block of amino acid remobilization and growth inhibition. Taken together, TaATLa1.1-3A, -3B, and -3D contribute substantially to Arabidopsis and wheat growth. We propose that TaATLa1.1-3A, -3B, and -3D may participate in the source-sink translocation of amino acid, and they may have profound implications for wheat yield improvement.

Fluorescent Auxin Analogs Report Two Auxin Binding Sites with Different Subcellular Distribution and Affinities: A Cue for Non-Transcriptional Auxin Signaling

The complexity of auxin signaling is partially due to multiple auxin receptors that trigger differential signaling. To obtain insight into the subcellular localization of auxin-binding sites, we used fluorescent auxin analogs that can undergo transport but do not deploy auxin signaling. Using fluorescent probes for different subcellular compartments, we can show that the fluorescent analog of 1-naphthaleneacetic acid (NAA) associates with the endoplasmic reticulum (ER) and tonoplast, while the fluorescent analog of indole acetic acid (IAA) binds to the ER. The binding of the fluorescent NAA analog to the ER can be outcompeted by unlabeled NAA, which allows us to estimate the affinity of NAA for this binding site to be around 1 μM. The non-transportable auxin 2,4-dichlorophenoxyacetic acid (2,4-D) interferes with the binding site for the fluorescent NAA analog at the tonoplast but not with the binding site for the fluorescent IAA analog at the ER. We integrate these data into a working model, where the tonoplast hosts a binding site with a high affinity for 2,4-D, while the ER hosts a binding site with high affinity for NAA. Thus, the differential subcellular localization of binding sites reflects the differential signaling in response to these artificial auxins.

Mechanotransduction in the spotlight of mechano-sensitive channels

The study of mechanosensitive channels (MS) in living organisms has progressed considerably over the past two decades. The understanding of their roles in mechanosensation and mechanotransduction was consecrated by the awarding of the Nobel Prize in 2021 to A. Patapoutian for his discoveries on the role of MS channels in mechanoperception in humans. In this review, we first summarize the fundamental properties of MS channels and their mode of operation. Then in a second step, we provide an update on the knowledge on the families of MS channels identified in plants and the roles and functions that have been attributed to them.

Molecular Mechanisms of Plant Responses to Salt Stress

Saline-alkali soils pose an increasingly serious global threat to plant growth and productivity. Much progress has been made in elucidating how plants adapt to salt stress by modulating ion homeostasis. Understanding the molecular mechanisms that affect salt tolerance and devising strategies to develop/breed salt-resilient crops have been the primary goals of plant salt stress signaling research over the past few decades. In this review, we reflect on recent major advances in our understanding of the cellular and physiological mechanisms underlying plant responses to salt stress, especially those involving temporally and spatially defined changes in signal perception, decoding, and transduction in specific organelles or cells.

A sorbitol transporter gene plays specific role in the occurrence of watercore by modulating the level of intercellular sorbitol in pear

Watercore is a physiological disorder which often occurs on the fruits of pear and closely related to the influence of environment factors, such as high temperature. The excessive accumulation of sorbitol in fruit intercellular space is considered to be an important cause of watercore. Sorbitol transporter (SOT) is the key translocation protein of sorbitol and our previous study found the PpSOT3 expression was significantly decreased in high temperature induced-watercore pear fruit by transcriptome method. How PpSOT3 regulates the occurrence of watercore in pear remains unclear. The present study found that PpSOT3 had different expression pattern in watercore-susceptible (Akibae and Hosui) and watercore-resistant (Aikansui) pear cultivars of young fruit and mature fruit. Moreover, the accumulation of intercellular sorbitol in watercore fruit was significantly higher than that in healthy fruit, and the expression of PpSOT3 was significantly inhibited. After the treatment of sugar transport inhibitor (para-chloromercuribenzenesulphonic acid, PCMBS), the fruit pulp occurred water-soaking and the expression of PpSOT3 and the intercellular sorbitol content was significantly decreased and increased, respectively. Subcellular localization showed that PpSOT3 was located in plasma membrane. Both transient overexpression and RNAi assays suggested PpSOT3 had the function of sorbitol uptake. Taken together, these results demonstrate that PpSOT3 was a PCMBS-sensitive sorbitol transporter and played an important role in the occurrence of watercore by modulating the level of intercellular sorbitol content.

Plant cell mechanobiology: Greater than the sum of its parts

The ability to sense and respond to physical forces is critical for the proper function of cells, tissues, and organisms across the evolutionary tree. Plants sense gravity, osmotic conditions, pathogen invasion, wind, and the presence of barriers in the soil, and dynamically integrate internal and external stimuli during every stage of growth and development. While the field of plant mechanobiology is growing, much is still poorly understood-including the interplay between mechanical and biochemical information at the single-cell level. In this review, we provide an overview of the mechanical properties of three main components of the plant cell and the mechanoperceptive pathways that link them, with an emphasis on areas of complexity and interaction. We discuss the concept of mechanical homeostasis, or "mechanostasis," and examine the ways in which cellular structures and pathways serve to maintain it. We argue that viewing mechanics and mechanotransduction as emergent properties of the plant cell can be a useful conceptual framework for synthesizing current knowledge and driving future research.

Sensing Mechanisms: Calcium Signaling Mediated Abiotic Stress in Plants

Plants are exposed to various environmental stresses. The sensing of environmental cues and the transduction of stress signals into intracellular signaling are initial events in the cellular signaling network. As a second messenger, Ca²⁺ links environmental stimuli to different biological processes, such as growth, physiology, and sensing of and response to stress. An increase in intracellular calcium concentrations ([Ca²⁺]_i) is a common event in most stress-induced signal transduction pathways. In recent years, significant progress has been made in research related to the early events of stress signaling in plants, particularly in the identification of primary stress sensors. This review highlights current advances that are beginning to elucidate the mechanisms by which abiotic environmental cues are sensed via Ca²⁺ signals. Additionally, this review discusses important questions about the integration of the sensing of multiple stress conditions and subsequent signaling responses that need to be addressed in the future.

Physiological and photochemical evaluation of pepper methionine sulfoxide reductase B2 (CaMsrB2) expressing transgenic rice in saline habitat

Two pepper methionine sulfoxide reductase B2 (CaMsrB2) gene expressing transgenic rice lines (L-8 and L-23) were interrogated with respect to their physiological and photochemical attributes along with control (WT, Ilmi) as a standard against varying levels of salt concentration which are 75 mM, 150 mM and 225 mM. Against various levels of salt (NaCl) concentration, recurring detrimental effects of extreme salt stress was observed and more pronounced in the wild type plants as compared to our transgenic lines. As the exacerbated effects of salinity is responsible for pushing the plants to their ecological tolerance, our transgenic lines performed well uplifted in different realms of physiology and photochemistry such as relative water content (RWC = 60-75%), stomatal conductance (g_s = 70-190 mmolm^-2s^-1), performance index (PI_ABS = 1.0-4.5), maximal photochemical yield of PSII (F_V/F_M = 0.48-0.72) and chlorophyll content index (CCI = 5-7.2 au) in comparison to the control. Relative gene expression, ion analysis and antioxidants activity were analyzed in all treatments to ensure the hypothesis obtained from data of physiology and photochemistry. Photosynthetic apparatus is known to lose energy in various forms such as NPQ, DI_O/CS, damages of reaction center (F_V/F_O) which are the markers of poor health were clearly decreased in the L-23 line as compared to L-8 and WT. Present study revealed the protruding tolerance of L-23 and L-8 transgenic lines with L-23 line in the lead in comparison to control and L-8 transgenic lines.

Comparative phylogenetic analysis of CBL reveals the gene family evolution and functional divergence in Saccharum spontaneum

BACKGROUND

The identification and functional analysis of genes that improve tolerance to low potassium stress in S. spontaneum is crucial for breeding sugarcane cultivars with efficient potassium utilization. Calcineurin B-like (CBL) protein is a calcium sensor that interacts with specific CBL-interacting protein kinases (CIPKs) upon plants' exposure to various abiotic stresses.

RESULTS

In this study, nine CBL genes were identified from S. spontaneum. Phylogenetic analysis of 113 CBLs from 13 representative plants showed gene expansion and strong purifying selection in the CBL family. Analysis of CBL expression patterns revealed that SsCBL01 was the most commonly expressed gene in various tissues at different developmental stages. Expression analysis of SsCBLs under low K⁺ stress indicated that potassium deficiency moderately altered the transcription of SsCBLs. Subcellular localization showed that SsCBL01 is a plasma membrane protein and heterologous expression in yeast suggested that, while SsCBL01 alone could not absorb K⁺, it positively regulated K⁺ absorption mediated by the potassium transporter SsHAK1.

CONCLUSIONS

This study provided insights into the evolution of the CBL gene family and preliminarily demonstrated that the plasma membrane protein SsCBL01 was involved in the response to low K⁺ stress in S. spontaneum.

Multiomics reveal pivotal roles of sodium translocation and compartmentation in regulating salinity resistance in allotetraploid rapeseed

The large size and complexity of the allotetraploid rapeseed (Brassica napus) genome present huge challenges for understanding salinity resistance in this important crop. In this study, we identified two rapeseed genotypes with significantly different degrees of salinity resistance and examined the underlying mechanisms using an integrated analysis of phenomics, ionomics, genomics, and transcriptomics. Under salinity, a higher accumulation of osmoregulation substances and better root-system architecture was observed in the resistant genotype, H159, than in the sensitive one, L339. A lower shoot Na+ concentration and a higher root vacuolar Na+ concentration indicated lower root-to-shoot translocation and higher compartmentation in H159 than in L339. Whole-genome re-sequencing (WGRS) and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in abiotic stress responses and ion transport. Combining ionomics with transcriptomics identified plasma membrane-localized BnaC2.HKT1;1 and tonoplast-localized BnaC5.NHX2 as the central factors regulating differential root xylem unloading and vacuolar sequestration of Na+ between the two genotypes. Identification of polymorphisms by WGRS and PCR revealed two polymorphic MYB-binding sites in the promoter regions that might determine the differential gene expression of BnaC2.HKT1;1 and BnaC5.NHX2. Our multiomics approach thus identified core transporters involved in Na+ translocation and compartmentation that regulate salinity resistance in rapeseed. Our results may provide elite gene resources for the improvement of salinity resistance in this crop, and our multiomics approach can be applied to other similar studies.

Plant electrical signals: A multidisciplinary challenge

Plant electrical signals, an early event in the plant-stimulus interaction, rapidly transmit information generated by the stimulus to other organs, and even the whole plant, to promote the corresponding response and trigger a regulatory cascade. In recent years, many promising state-of-the-art technologies applicable to study plant electrophysiology have emerged. Research focused on expression of genes associated with electrical signals has also proliferated. We propose that it is appropriate for plant electrical signals to be considered in the form of a "plant electrophysiological phenotype". This review synthesizes research on plant electrical signals from a novel, interdisciplinary perspective, which is needed to improve the efficient aggregation and use of plant electrical signal data and to expedite interpretation of plant electrical signals.

Mix and match: Patchwork domain evolution of the land plant-specific Ca2+-permeable mechanosensitive channel MCA

Multidomain proteins can have a complex evolutionary history that may involve de novo domain evolution, recruitment and / or recombination of existing domains and domain losses. Here, the domain evolution of the plant-specific Ca²⁺-permeable mechanosensitive channel protein, MID1-COMPLEMENTING ACTIVITY (MCA), was investigated. MCA, a multidomain protein, possesses a Ca²⁺-influx-MCA^func domain and a PLAC8 domain. Profile Hidden Markov Models (HMMs) of domains were assessed in 25 viridiplantae proteomes. While PLAC8 was detected in plants, animals, and fungi, MCA^func was found in streptophytes but not in chlorophytes. Full MCA proteins were only found in embryophytes. We identified the MCA^func domain in all streptophytes including charophytes where it appeared in E3 ubiquitin ligase-like proteins. Our Maximum Likelihood (ML) analyses suggested that the MCA^func domain evolved early in the history of streptophytes. The PLAC8 domain showed similarity to Plant Cadmium Resistance (PCR) genes, and the coupling of MCA^func and PLAC8 seemed to represent a single evolutionary event. This combination is unique in MCA, and does not exist in other plant mechanosensitive channels. Within angiosperms, gene duplications increased the number of MCAs. Considering their role in mechanosensing in roots, MCA might be instrumental for the rise of land plants. This study provides a textbook example of de novo domain emergence, recombination, duplication, and losses, leading to the convergence of function of proteins in plants.

The calcium-dependent protein kinase ZmCDPK7 functions in heat-stress tolerance in maize

Global warming poses a serious threat to crops. Calcium-dependent protein kinases (CDPKs)/CPKs play vital roles in plant stress responses, but their exact roles in plant thermotolerance remains elusive. Here, we explored the roles of heat-induced ZmCDPK7 in thermotolerance in maize. ZmCDPK7-overexpressing maize plants displayed higher thermotolerance, photosynthetic rates, and antioxidant enzyme activity but lower H₂ O₂ and malondialdehyde (MDA) contents than wild-type plants under heat stress. ZmCDPK7-knockdown plants displayed the opposite patterns. ZmCDPK7 is attached to the plasma membrane but can translocate to the cytosol under heat stress. ZmCDPK7 interacts with the small heat shock protein sHSP17.4, phosphorylates sHSP17.4 at Ser-44 and the respiratory burst oxidase homolog RBOHB at Ser-99, and upregulates their expression. Site-directed mutagenesis of sHSP17.4 to generate a Ser-44-Ala substitution reduced ZmCDPK7's enhancement of catalase activity but enhanced ZmCDPK7's suppression of MDA accumulation in heat-stressed maize protoplasts. sHSP17.4, ZmCDPK7, and RBOHB were less strongly upregulated in response to heat stress in the abscisic acid-deficient mutant vp5 versus the wild type. Pretreatment with an RBOH inhibitor suppressed sHSP17.4 and ZmCDPK7 expression. Therefore, abscisic acid-induced ZmCDPK7 functions both upstream and downstream of RBOH and participates in thermotolerance in maize by mediating the phosphorylation of sHSP17.4, which might be essential for its chaperone function.

A new adenylyl cyclase, putative disease-resistance RPP13-like protein 3, participates in abscisic acid-mediated resistance to heat stress in maize

In plants, 3´,5´-cyclic adenosine monophosphate (cAMP) is an important second messenger with varied functions; however, only a few adenylyl cyclases (ACs) that synthesize cAMP have been identified. Moreover, the biological roles of ACs/cAMP in response to stress remain largely unclear. In this study, we used quantitative proteomics techniques to identify a maize heat-induced putative disease-resistance RPP13-like protein 3 (ZmRPP13-LK3), which has three conserved catalytic AC centres. The AC activity of ZmRPP13-LK3 was confirmed by in vitro enzyme activity analysis, in vivo RNAi experiments, and functional complementation in the E. coli cyaA mutant. ZmRPP13-LK3 is located in the mitochondria. The results of in vitro and in vivo experiments indicated that ZmRPP13-LK3 interacts with ZmABC2, a possible cAMP exporter. Under heat stress, the concentrations of ZmRPP13-LK3 and cAMP in the ABA-deficient mutant vp5 were significantly less than those in the wild-type, and treatment with ABA and an ABA inhibitor affected ZmRPP13-LK3 expression in the wild-type. Application of 8-Br-cAMP, a cAMP analogue, increased heat-induced expression of heat-shock proteins in wild-type plants and alleviated heat-activated oxidative stress. Taken together, our results indicate that ZmRPP13-LK3, a new AC, can catalyse ATP for the production of cAMP and may be involved in ABA-regulated heat resistance.

Programmed cell death (PCD) control in plants: New insights from the Arabidopsis thaliana deathosome

Programmed cell death (PCD) is a genetically controlled process that leads to cell suicide in both eukaryotic and prokaryotic organisms. In plants PCD occurs during development, defence response and when exposed to adverse conditions. PCD acts controlling the number of cells by eliminating damaged, old, or unnecessary cells to maintain cellular homeostasis. Unlike in animals, the knowledge about PCD in plants is limited. The molecular network that controls plant PCD is poorly understood. Here we present a review of the current mechanisms involved with the genetic control of PCD in plants. We also present an updated version of the AtLSD1 deathosome, which was previously proposed as a network controlling HR-mediated cell death in Arabidopsis thaliana. Finally, we discuss the unclear points and open questions related to the AtLSD1 deathosome.

A high activity zinc transporter OsZIP9 mediates zinc uptake in rice

Zinc (Zn) is an essential micronutrient for most organisms including humans, and Zn deficiency is widespread in human populations, particularly in underdeveloped regions. Cereals such as rice (Oryza sativa) are the major dietary source of Zn for most people. However, the molecular mechanism underlying Zn uptake in rice is still not fully understood. Here, we report that a member of the ZIP (ZRT, IRT-like protein) family, OsZIP9, contributes to Zn uptake in rice. It was expressed in the epidermal and exodermal cells of lateral roots, localized in the plasma membrane and induced during Zn deficiency. Yeast-expressed OsZIP9 showed much higher Zn influx transport activity than other rice ZIP proteins in a wide range of Zn concentrations. OsZIP9 knockout rice plants showed a significant reduction in growth at low Zn concentrations, but could be rescued by a high Zn supply. Compared with the wild type, accumulation of Zn in root, shoot and grain was much lower in knockout lines, particularly with a low supply of Zn under both hydroponic and paddy soil conditions. OsZIP9 also showed Co uptake activity. Natural variation of OsZIP9 expression level is highly associated with Zn content in milled grain among rice varieties in the germplasm collection. Taken together, these results show that OsZIP9 is an important influx transporter responsible for the take up of Zn and Co from external media into root cells.

CsSWEET1a and CsSWEET17 Mediate Growth and Freezing Tolerance by Promoting Sugar Transport across the Plasma Membrane

Sugars Will Eventually be Exported Transporters (SWEETs) are important in plant biological processes. Expression levels of CsSWEET1a and CsSWEET17 are induced by cold acclimation (CA) and cold stress in Camellia sinensis. Here, we found that CsSWEET17 was alternatively spliced, and its exclusion (Ex) transcript was associated with the CA process. Both plasma membrane-localized CsSWEET1a and CsSWEET17 transport hexoses, but cytoplasm-localized CsSWEET17-Ex does not. These results indicate that alternative splicing may be involved in regulating the function of SWEET transporters in response to low temperature in plants. The extra C-terminal of CsSWEET17, which is not found in the tonoplast fructose transporter AtSWEET17, did not affect its plasma membrane localization but promoted its sugar transport activities. The overexpression (OE) of CsSWEET1a and CsSWEET17 genes resulted in an increased sugar uptake in Arabidopsis, affecting plant germination and growth. The leaf and seed sizes of the CsSWEET17-OE lines were significantly larger than those of the wild type. Moreover, the OE of CsSWEET1a and CsSWEET17 significantly reduced the relative electrolyte leakage levels under freezing stress. Compared with the wild type, the expression of AtCWINV genes was suppressed in both CsSWEET1a-OE and CsSWEET17-OE lines, indicating the alteration in sugar contents in the cell walls of the OE lines. Furthermore, the interaction between CsSWEET1a and CsSWEET17 was confirmed using yeast two-hybrid and bimolecular fluorescence complementation assays. We showed that CsSWEET1a and CsSWEET17 form homo-/heterodimers in the plasma membrane and mediate the partitioning of sugars between the cytoplasm and the apoplast, thereby regulating plant growth and freezing tolerance.

The Mechanosensitive Ion Channel MSL10 Potentiates Responses to Cell Swelling in Arabidopsis Seedlings

The ability to respond to unanticipated increases in volume is a fundamental property of cells, essential for cellular integrity in the face of osmotic challenges. Plants must manage cell swelling during flooding, rehydration, and pathogen invasion-but little is known about the mechanisms by which this occurs. It has been proposed that plant cells could sense and respond to cell swelling through the action of mechanosensitive ion channels. Here, we characterize a new assay to study the effects of cell swelling on Arabidopsis thaliana seedlings and to test the contributions of the mechanosensitive ion channel MscS-like10 (MSL10). The assay incorporates both cell wall softening and hypo-osmotic treatment to induce cell swelling. We show that MSL10 is required for several previously demonstrated responses to hypo-osmotic shock, including a cytoplasmic calcium transient within the first few seconds, accumulation of ROS within the first 30 min, and increased transcript levels of mechano-inducible genes within 60 min. We also show that cell swelling induces programmed cell death within 3 h in a MSL10-dependent manner. Finally, we show that MSL10 is unable to potentiate cell swelling-induced death when phosphomimetic residues are introduced into its soluble N terminus. Thus, MSL10 functions as a phospho-regulated membrane-based sensor that connects the perception of cell swelling to a downstream signaling cascade and programmed cell death.

Analyzing plant mechanosensitive ion channels expressed in giant E. coli spheroplasts by single-channel patch-clamp electrophysiology

Plants possess numerous ion channels that respond to a range of stimuli, including small molecules, transmembrane voltage, and mechanical force. Many in the latter category, known as mechanosensitive (MS) ion channels, open directly in response to increases in lateral membrane tension. One of the most effective techniques for characterizing ion channel properties is patch-clamp electrophysiology, in which the current through a section of membrane containing ion channels is measured. For MS channels, this technique enables the measurement of key channel properties such as tension sensitivity, conductance, and ion selectivity. These characteristics, along with the phenotypes of genetic mutants, can help reveal the physiological roles of a particular MS channel. In this protocol, we provide detailed instructions on how to study MS ion channels using single-channel patch-clamp electrophysiology in giant E. coli spheroplasts. We first present an optimized method for preparing giant spheroplasts, then describe how to measure MS channel activity using patch-clamp electrophysiology and analyze the resulting data. We also provide recommended equipment lists, setup schematics, and useful conventions.

Plasma Membrane Ca2+ Permeable Mechanosensitive Channel OsDMT1 Is Involved in Regulation of Plant Architecture and Ion Homeostasis in Rice

Plant architecture is an important factor for crop production. Plant height, tiller pattern, and panicle morphology are decisive factors for high grain yield in rice. Here, we isolated and characterized a T-DNA insertion rice mutant Osdmt1 (Oryza sativa dwarf and multi-tillering1) that exhibited a severe dwarf phenotype and multi-tillering. Molecular cloning revealed that DMT1 encodes a plasma membrane protein that was identified as a putative Ca²⁺ permeable mechanosensitive channel. The transcript expression level was significantly higher in the dmt1 mutant compared to wild type (WT). Additionally, the dmt1 homozygous mutant displayed a stronger phenotype than that of the WT and heterozygous seedlings after gibberellic acid (GA) treatment. RNA-seq and iTRAQ-based proteome analyses were performed between the dmt1 mutant and WT. The transcriptome profile revealed that several genes involved in GA and strigolactone (SL) biosyntheses were altered in the dmt1 mutant. Ca²⁺ and other ion concentrations were significantly enhanced in the dmt1 mutant, suggesting that DMT1 contributes to the accumulation of several ions in rice. Moreover, several EF-hand Ca²⁺ sensors, including CMLs (CaM-like proteins) and CDPKs (calcium-dependent protein kinases), displayed markedly altered transcript expression and protein levels in the dmt1 mutant. Overall, these findings aid in the elucidation of the multiply regulatory roles of OsDMT1/OsMCA1 in rice.

Targeted Mutagenesis of the Rice FW 2.2-Like Gene Family Using the CRISPR/Cas9 System Reveals OsFWL4 as a Regulator of Tiller Number and Plant Yield in Rice

The FW2.2-like (FWL) genes encode cysteine-rich proteins with a placenta-specific 8 domain. They play roles in cell division and organ size control, response to rhizobium infection, and metal ion homeostasis in plants. Here, we target eight rice FWL genes using the CRISPR/Cas9 system delivered by Agrobacterium-mediated transformation. We successfully generate transgenic T₀ lines for 15 of the 16 targets. The targeted mutations are detected in the T₀ lines of all 15 targets and the average mutation rate is found to be 81.6%. Transfer DNA (T-DNA) truncation is a major reason for the failure of mutagenesis in T₀ plants. T-DNA segregation analysis reveals that the T-DNA inserts in transgenic plants can be easily eliminated in the T₁ generation. Of the 30 putative off-target sites examined, unintended mutations are detected in 13 sites. Phenotypic analysis reveals that tiller number and plant yield of OsFWL4 gene mutants are significantly greater than those of the wild type. Flag leaves of OsFWL4 gene mutants are wider than those of the wild type. The increase in leaf width of the mutants is caused by an increase in cell number. Additionally, grain length of OsFWL1 gene mutants is higher than that of the wild type. Our results suggest that transgene-free rice plants with targeted mutations can be produced in the T₁ generation using the Agrobacterium-mediated CRISPR/Cas9 system and that the OsFWL4 gene is a negative regulator of tiller number and plant yield.

Prolonged oxygen depletion in microwounded cells of Chara corallina detected with novel oxygen nanosensors

Primary physicochemical steps in microwounding of plants were investigated using electrochemical nano- and microprobes, with a focus on the role of oxygen in the wounding responses of individual plant cells. Electrochemical measurements of cell oxygen content were made with carbon-filled quartz micropipettes with platinum-coated tips (oxygen nanosensors). These novel platinum nanoelectrodes are useful for understanding cell oxygen metabolism and can be employed to study the redox biochemistry and biology of cells, tissues and organisms. We show here that microinjury of Chara corallina internodal cells with the tip of a glass micropipette is associated with a drastic decrease in oxygen concentration at the vicinity of the stimulation site. This decrease is reversible and lasts for up to 40 minutes. Membrane stretching, calcium influx, and cytoskeleton rearrangements were found to be essential for the localized oxygen depletion induced by cell wall microwounding. Inhibition of electron transport in chloroplasts or mitochondria did not affect the magnitude or timing of the observed response. In contrast, the inhibition of NADPH oxidase activity caused a significant reduction in the amplitude of the decrease in oxygen concentration. We suggest that the observed creation of localized anoxic conditions in response to cell wall puncture might be mediated by NADPH oxidase.

Identification of the magnesium transport (MGT) family in Poncirus trifoliata and functional characterization of PtrMGT5 in magnesium deficiency stress

At least eight MGT genes were identified in citrus and PtrMGT5 plays important role in maintaining Mg homeostasis in citrus by getting involved in the Mg absorption and transport. Magnesium (Mg) is an essential macronutrient for plant growth and development, and the magnesium transporter (MGT) genes participate in mediate Mg²⁺ uptake, translocation and sequestration into cellular storage compartments. Although several MGT genes have been characterized in various plant species, a comprehensive analysis of the MGT gene family in citrus is still uncharacterized. In this study, eight PtrMGT genes were identified through genome-wide analyses. Phylogenetic analyses revealed that PtrMGT genes were classified into five distinct subfamilies. A quantitative RT-PCR analysis showed that eight PtrMGT genes were expressed in all of the detected tissues and they mainly expressed in the vegetative organs. Expression analyses revealed the PtrMGT genes responded to various Mg deficiency stresses, including absolute Mg deficiency and antagonistic Mg deficiency which caused by low pH or Al toxicity. PtrMGT5, which localizes to the plasma membrane and was transcriptionally active, was functionally characterized. PtrMGT5 overexpression considerably enhanced absolute Mg deficiency and antagonistic Mg deficiency tolerance in transgenic Arabidopsis plants, which was accompanied by increased fresh weight and Mg content, whereas opposite changes were observed when PtrMGT5 homolog in Valencia Orange callus was knocked down. Taken together, PtrMGT5 plays important role in maintaining Mg homeostasis in citrus by getting involved in the Mg absorption and transport.

Analysis of the role of geranylgeranyl diphosphate synthase 8 from Tripterygium wilfordii in diterpenoids biosynthesis

Tripterygium wilfordii is known to contain various types of bioactive diterpenoids that exhibit many remarkable activities. Many studies have recently been targeted toward the elucidation of the diterpenoids biosynthetic pathways in attempts to obtain these compounds with a view to solving the dilemma of low yield in plants. However, the short-chain prenyltransferases (SC-PTSs) responsible for the formation of geranylgeranyl diphosphate (GGPP), a crucial precursor for synthesizing the skeleton structures of diterpenoids, have not been characterized in depth. Here, T. wilfordii transcriptome data were used to identify eight putative GGPPSs, including two small subunits of geranyl diphosphate synthase (GPPS.SSU). Of them, GGPPS1, GGPPS7, GGPPS8, GPPS.SSU II and GPPS.SSU were translocated mainly into chloroplasts, and GGPPS8 exhibited the optimal catalytic efficiency with respect to catalyzing the formation of GGPP. In addition, the expression pattern of GGPPS8 was similar to that of downstream terpene synthase genes that are directly correlated with triptolide production in roots, indicating that GGPPS8 was most likely to participate in triptolide biosynthesis in roots among the studied enzymes. GPPS.SSU was inactive alone but interacted with GGPPS1, GGPPS7 and GGPPS8 to change the product from GGPP to GPP. These findings implicate that these candidate genes can be regulated to shift the metabolic flux toward diterpenoid formation, increasing the yields of bioactive diterpenoids in plants.

The Amino Acid Permease 5 (OsAAP5) Regulates Tiller Number and Grain Yield in Rice

As fundamental nutrients, amino acids are important for rice (Oryza sativa) growth and development. Here, we identified the amino acid permease 5 (OsAAP5), that regulates tiller number and grain yield in rice. The OsAAP5 promoter sequence differed between indica and japonica rice varieties. Lower expression of OsAAP5 in the young leaf blade in indica varieties than in japonica varieties was associated with more tillers in indica than in japonica Down-regulation of OsAAP5 expression in japonica using RNA interference (RNAi) and clustered regularly interspaced short palindromic repeats led to increases in tiller number and grain yield, whereas OsAAP5 overexpression (OE) had the opposite effect. Both a protoplast amino acid uptake assay and HPLC analysis indicated that more basic (Lys, Arg) and neutral (Val, Ala) amino acids were transported and accumulated in the OE lines than in the wild type, but the opposite was observed in the RNAi lines. Furthermore, exogenous application of Lys, Arg, Val, and Ala in the OE lines substantially inhibited tiller bud elongation, but the effect was lost in the RNAi lines. Notably, concentrations of the cytokinins cis-zeatin and dihydrozeatin were much lower in the OE lines than in the wild type, whereas concentrations in the RNAi lines were higher. Thus, OsAAP5 could regulate tiller bud outgrowth by affecting cytokinin levels, and knockout of OsAAP5 could be valuable for japonica breeding programs seeking high yield and grain quality.

Increased Autophagy of Rice Can Increase Yield and Nitrogen Use Efficiency (NUE)

Autophagy (self-eating), a conserved pathway in eukaryotes, which is designed to handle cytoplasmic material in bulk and plays an important role in the remobilization of nutrient, such as nitrogen (N) under suboptimal nutrient conditions. Here, we identified a core component of an autophagy gene in rice (Oryza sativa), OsATG8a, with increased expression levels under N starvation conditions. Overexpression of OsATG8a significantly enhanced the level of autophagy and the number of effective tillers in the transgenic rice. In addition, the transgenic lines accumulated more N in grains than in the dry remains and the yield was significantly increased under normal N conditions. Further N allocation studies revealed that the nitrogen uptake efficiency (NUpE) and nitrogen use efficiency (NUE) significantly increased. Otherwise, under suboptimal N conditions, overexpression of OsATG8a did not seem to have any effect on yield and NUE, but NUpE was still improved significantly. Based on our findings, we consider OsATG8a to be a great candidate gene to increase NUE and yield.

Enhanced elevations of hypo-osmotic shock-induced cytosolic and nucleic calcium concentrations in tobacco cells by pretreatment with dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is a dipolar aprotic solvent widely used in biological assays. Here, we observed that DMSO enhanced the hypo-osmotically induced increases in the concentration of Ca2+ in cytosolic and nucleic compartments in the transgenic cell-lines of tobacco (BY-2) expressing aequorin.

Overexpression of rice aquaporin OsPIP1;2 improves yield by enhancing mesophyll CO2 conductance and phloem sucrose transport

Aquaporins are involved in CO2 transport from the leaf intercellular air space to the chloroplast, which contributes to CO2 assimilation. However, the mechanism of CO2 transport by rice (Oryza sativa L.) aquaporins is unknown. Here, we investigated the function of the aquaporin OsPIP1;2 in CO2 diffusion-associated photosynthesis and phloem sucrose transport. Moreover, the grain yield of rice lines overexpressing OsPIP1;2 was determined. OsPIP1;2 was localized to the plasma membrane and the relative expression of OsPIP1;2 was approximately 5-fold higher in leaves in the presence of an elevated CO2 concentration. Overexpression of OsPIP1;2 increased mesophyll conductance by approximately 150% compared with wild-type (WT) rice. The OsPIP1;2-overexpressing lines had higher biomass than the WT, possibly due to increased phloem sucrose transport. In addition, the grain yield of OsPIP1;2-overexpressing lines was approximately 25% higher than that of the WT in three-season field experiments, due to the increased numbers of effective tillers and spikelets per panicle. Our results suggest that OsPIP1;2 modulates rice growth and grain yield by facilitating leaf CO2 diffusion, which increases both the net CO2 assimilation rate and sucrose transport.

Revising the PLAC8 gene family: from a central role in differentiation, proliferation, and apoptosis in mammals to a multifunctional role in plants

PLAC8 is a cysteine-rich protein described as a central mediator of tumor evolution in mammals; as such, it represents a promising candidate for diagnostic and therapeutic targeting. The human PLAC8 gene is also involved in contact hypersensitivity response and presents a role in psoriatic skin. In plants, PLAC8 motif-containing proteins are involved in the determination of organ size and growth, response to infection, Ca2+ influx, Cd resistance, and zinc detoxification. In general, PLAC8 motif-containing proteins present the conserved CCXXXXCPC or CLXXXXCPC region. However, there is no devised nomenclature for the PLAC8 motif-containing proteins. Here, through the analysis of 445 sequences, we show that PLAC8 motif-containing proteins constitute a unique gene family, and we propose a unified nomenclature. This is the first report indicating the existence of different groups of PLAC8 proteins, which we have called types I, II, and III. Type I genes are found in mammals, fungi, plants, and algae, and types II and III are exclusive to plants. Our study describes for the first time PLAC8 type III proteins. Whether these sequences maintain their known functional role or possess distinct functions of types I and II genes remains unclear.

Structure of the hyperosmolality-gated calcium-permeable channel OSCA1.2

In plants, hyperosmolality stimuli triggers opening of the osmosensitive channels, leading to a rapid downstream signaling cascade initiated by cytosolic calcium concentration elevation. Members of the OSCA family in Arabidopsis thaliana, identified as the hyperosmolality-gated calcium-permeable channels, have been suggested to play a key role during the initial phase of hyperosmotic stress response. Here, we report the atomic structure of Arabidopsis OSCA1.2 determined by single-particle cryo-electron microscopy. It contains 11 transmembrane helices and forms a homodimer. It is in an inactivated state, and the pore-lining residues are clearly identified. Its cytosolic domain contains a RNA recognition motif and two unique long helices. The linker between these two helices forms an anchor in the lipid bilayer and may be essential to osmosensing. The structure of AtOSCA1.2 serves as a platform for the study of the mechanism underlying osmotic stress responses and mechanosensing.

In plants, hyperosmolality stimuli triggers opening of the osmosensitive channels, leading to a rapid downstream signaling cascade. Here, the authors solve the cryo-EM structure of an osmosensitive channel from Arabidopsis OSCA1.2 in its inactivated state.

Hitting the Wall-Sensing and Signaling Pathways Involved in Plant Cell Wall Remodeling in Response to Abiotic Stress

Plant cells are surrounded by highly dynamic cell walls that play important roles regulating aspects of plant development. Recent advances in visualization and measurement of cell wall properties have enabled accumulation of new data about wall architecture and biomechanics. This has resulted in greater understanding of the dynamics of cell wall deposition and remodeling. The cell wall is the first line of defense against different adverse abiotic and biotic environmental influences. Different abiotic stress conditions such as salinity, drought, and frost trigger production of Reactive Oxygen Species (ROS) which act as important signaling molecules in stress activated cellular responses. Detection of ROS by still-elusive receptors triggers numerous signaling events that result in production of different protective compounds or even cell death, but most notably in stress-induced cell wall remodeling. This is mediated by different plant hormones, of which the most studied are jasmonic acid and brassinosteroids. In this review we highlight key factors involved in sensing, signal transduction, and response(s) to abiotic stress and how these mechanisms are related to cell wall-associated stress acclimatization. ROS, plant hormones, cell wall remodeling enzymes and different wall mechanosensors act coordinately during abiotic stress, resulting in abiotic stress wall acclimatization, enabling plants to survive adverse environmental conditions.

Calcium transport across plant membranes: mechanisms and functions

Contents Summary 49 I. Introduction 49 II. Physiological and structural characteristics of plant Ca²⁺ -permeable ion channels 50 III. Ca²⁺ extrusion systems 61 IV. Concluding remarks 64 Acknowledgements 64 References 64 SUMMARY: Calcium is an essential structural, metabolic and signalling element. The physiological functions of Ca²⁺ are enabled by its orchestrated transport across cell membranes, mediated by Ca²⁺ -permeable ion channels, Ca²⁺ -ATPases and Ca²⁺ /H⁺ exchangers. Bioinformatics analysis has not determined any Ca²⁺ -selective filters in plant ion channels, but electrophysiological tests do reveal Ca²⁺ conductances in plant membranes. The biophysical characteristics of plant Ca²⁺ conductances have been studied in detail and were recently complemented by molecular genetic approaches. Plant Ca²⁺ conductances are mediated by several families of ion channels, including cyclic nucleotide-gated channels (CNGCs), ionotropic glutamate receptors, two-pore channel 1 (TPC1), annexins and several types of mechanosensitive channels. Key Ca²⁺ -mediated reactions (e.g. sensing of temperature, gravity, touch and hormones, and cell elongation and guard cell closure) have now been associated with the activities of specific subunits from these families. Structural studies have demonstrated a unique selectivity filter in TPC1, which is passable for hydrated divalent cations. The hypothesis of a ROS-Ca²⁺ hub is discussed, linking Ca²⁺ transport to ROS generation. CNGC inactivation by cytosolic Ca²⁺ , leading to the termination of Ca²⁺ signals, is now mechanistically explained. The structure-function relationships of Ca²⁺ -ATPases and Ca²⁺ /H⁺ exchangers, and their regulation and physiological roles are analysed.

Whole Genome Analysis of Cyclin Dependent Kinase (CDK) Gene Family in Cotton and Functional Evaluation of the Role of CDKF4 Gene in Drought and Salt Stress Tolerance in Plants

Cotton (Gossypium spp.) is the number one crop cultivated for fiber production and the cornerstone of the textile industry. Drought and salt stress are the major abiotic stresses, which can have a huge economic impact on cotton production; this has been aggravated with continued climate change, and compounded by pollution. Various survival strategies evolved by plants include the induction of various stress responsive genes, such as cyclin dependent kinases (CDKs). In this study, we performed a whole-genome identification and analysis of the CDK gene family in cotton. We identified 31, 12, and 15 CDK genes in G. hirsutum, G. arboreum, and G. raimondii respectively, and they were classified into 6 groups. CDK genes were distributed in 15, 10, and 9 linkage groups of AD, D, and A genomes, respectively. Evolutionary analysis revealed that segmental types of gene duplication were the primary force underlying CDK genes expansion. RNA sequence and RT-qPCR validation revealed that Gh_D12G2017 (CDKF4) was strongly induced by drought and salt stresses. The transient expression of Gh_D12G2017-GFP fusion protein in the protoplast showed that Gh_D12G2017 was localized in the nucleus. The transgenic Arabidopsis lines exhibited higher concentration levels of the antioxidant enzymes measured, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) concentrations under drought and salt stress conditions with very low levels of oxidants. Moreover, cell membrane stability (CMS), excised leaf water loss (ELWL), saturated leaf weight (SLW), and chlorophyll content measurements showed that the transgenic Arabidopsis lines were highly tolerant to either of the stress factors compared to their wild types. Moreover, the expression of the stress-related genes was also significantly up-regulated in Gh_D12G2017(CDKF4) transgenic Arabidopsis plants under drought and salt conditions. We infer that CDKF-4s and CDKG-2s might be the primary regulators of salt and drought responses in cotton.

The involvement of calmodulin and protein kinases in the upstream of cytosolic and nucleic calcium signaling induced by hypoosmotic shock in tobacco cells

Changes in Ca2+ concentrations in cytosol ([Ca2+]C) or nucleus ([Ca2+]N) may play some vital roles in plants under hypoosmotic shock (Hypo-OS). Here, we observed that Hypo-OS induces biphasic increases in [Ca2+]C and [Ca2+]N in two tobacco cell lines (BY-2) expressing apoaequorin either in the cytosol or in the nucleus. Both [Ca2+]C and [Ca2+]N were sensitively modulated by the inhibitors of calmodulin and protein kinases, supporting the view that calmodulin suppresses the 1st peaks and and protein kinases enhance 2nd peaks in [Ca2+]C and [Ca2+]N. Data also suggested that the 1st and 2nd events depend on the internal and extracellular Ca2+ sources, respectively.