Comprehensive analyses of the annexin (ANN) gene family in Brassica rapa, Brassica oleracea and Brassica napus reveals their roles in stress response

Calcium-binding protein OsANN1 regulates rice blast disease resistance by inactivating jasmonic acid signaling

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases in rice (Oryza sativa L.). Plant annexins are calcium- and lipid-binding proteins that have multiple functions; however, the biological roles of annexins in plant disease resistance remain unknown. Here, we report a rice annexin gene, OsANN1 (Rice annexin 1), that was induced by M. oryzae infection and negatively regulated blast disease resistance in rice. By yeast 2-hybrid screening, we found that OsANN1 interacted with a cytochrome P450 monooxygenase, HAN1 ("HAN" termed "chilling" in Chinese), which has been reported to catalyze the conversion of biologically active jasmonoyl-L-isoleucine (JA-Ile) to the inactive form 12-hydroxy-JA-Ile. Pathogen inoculation assays revealed that HAN1 was also a negative regulator in rice blast resistance. Genetic evidence showed that OsANN1 acts upstream of HAN1. OsANN1 stabilizes HAN1 in planta, resulting in the inactivation of the endogenous biologically active JA-Ile. Taken together, our study unravels a mechanism where an OsANN1-HAN1 module impairs blast disease resistance via inactivating biologically active JA-Ile and JA signaling in rice.

Transcriptome studies on cadmium tolerance and biochar mitigating cadmium stress in muskmelon

Cadmium pollution in agricultural soil is a great threat to crop growth and human health. In this research, with 1%, 3% and 5% biochar applied to control soil cadmium pollution, melon was selected to be the experimental object for physiological detection and transcriptome analysis, through which we explored the mechanism of cadmium tolerance and biochar mitigating cadmium stress in muskmelon. Three set concentrations of biochar have a mitigative effect on muskmelon cadmium stress, and 5% biochar and 3% biochar respectively have the best and the worst alleviative effect. The alleviation of biochar to cadmium stress on muskmelon is primarily in the manner of inhibiting cadmium transfer, while the resistance of muskmelon to cadmium stress is through activating phenylpropanoid pathway and overexpressing stress related genes. Under cadmium treatment, 11 genes of the phenylpropane pathway and 19 stress-related genes including cytochrome P450 family protein genes and WRKY transcription factor genes were up-regulated, while 1%, 3%, 5% biochar addition significantly downregulated 3, 0, 7 phenylpropane pathway genes and 17, 5, 16 stress-related genes, respectively. Genes such as cytochrome P450 protein family genes, WRKY transcription factor genes, and annexin genes may play a key role in muskmelon's resistance to cadmium stress. The results show the key pathways and genes of cadmium stress resistance and the effect of different concentrations of biochar in alleviating cadmium stress, which provide a reference for the research of cadmium stress resistance in crops and the application of biochar in cadmium pollution in agricultural soil.

Grapevine bZIP transcription factor bZIP45 regulates VvANN1 and confers drought tolerance in Arabidopsis

Drought is a severe environmental condition that restricts the vegetative growth and reduces the yield of grapevine (Vitis vinifera L.). However, the mechanisms underlying grapevine response and adaptation to drought stress remain unclear. In the present study, we characterized an ANNEXIN gene, VvANN1, which plays a positive role in the drought stress response. The results indicated that VvANN1 was significantly induced by osmotic stress. Expression of VvANN1 in Arabidopsis thaliana enhanced osmotic and drought tolerance through modulating the level of MDA, H₂O₂, and O₂ ^·- at the seedling stage, implying that VvANN1 might be involved in the process of ROS homeostasis under drought or osmotic stress conditions. Moreover, we used yeast one-hybridization and chromatin immunoprecipitation assays to show that VvbZIP45 could regulate VvANN1 expression by directly binding to the promoter region of VvANN1 in response to drought stress. We also generated transgenic Arabidopsis that constitutively expressed the VvbZIP45 gene (35S::VvbZIP45) and further produced VvANN1Pro::GUS/35S::VvbZIP45 Arabidopsis plants via crossing. The genetic analysis results subsequently indicated that VvbZIP45 could enhance GUS expression in vivo under drought stress. Our findings suggest that VvbZIP45 may modulate VvANN1 expression in response to drought stress and reduce the impact of drought on fruit quality and yield.

Genome-wide analysis of annexin gene family in Schrenkiella parvula and Eutrema salsugineum suggests their roles in salt stress response

Annexins (Anns) play an important role in plant development, growth and responses to various stresses. Although Ann genes have been characterized in some plants, their role in adaptation mechanisms and tolerance to environmental stresses have not been studied in extremophile plants. In this study, Ann genes in Schrenkiella parvula and Eutrema salsugineum were identified using a genome-wide method and phylogenetic relationships, subcellular distribution, gene structures, conserved residues and motifs and also promoter prediction have been studied through bioinformatics analysis. We identified ten and eight encoding putative Ann genes in S. parvula and E. salsugineum genome respectively, which were divided into six subfamilies according to phylogenetic relationships. By observing conservation in gene structures and protein motifs we found that the majority of Ann members in two extremophile plants are similar. Furthermore, promoter analysis revealed a greater number of GATA, Dof, bHLH and NAC transcription factor binding sites, as well as ABRE, ABRE3a, ABRE4, MYB and Myc cis-acting elements in compare to Arabidopsis thaliana. To gain additional insight into the putative roles of candidate Ann genes, the expression of SpAnn1, SpAnn2 and SpAnn6 in S. parvula was studied in response to salt stress, which indicated that their expression level in shoot increased. Similarly, salt stress induced expression of EsAnn1, 5 and 7, in roots and EsAnn1, 2 and 5 in leaves of E. salsugineum. Our comparative analysis implies that both halophytes have different regulatory mechanisms compared to A. thaliana and suggest SpAnn2 gene play important roles in mediating salt stress.

Comprehensive Analyses of the Histone Deacetylases Tuin (HDT) Gene Family in Brassicaceae Reveals Their Roles in Stress Response

Histone deacetylases tuin (HDT) is a plant-specific protein subfamily of histone deacetylation enzymes (HDAC) which has a variety of functions in plant development, hormone signaling and stress response. Although the HDT family's genes have been studied in many plant species, they have not been characterized in Brassicaceae. In this study, 14, 8 and 10 HDT genes were identified in Brassica napus, Brassica rapa and Brassica oleracea, respectively. According to phylogenetic analysis, the HDTs were divided into four groups: HDT1(HD2A), HDT2(HD2B), HDT3(HD2C) and HDT4(HD2D). There was an expansion of HDT2 orthologous genes in Brassicaceae. Most of the HDT genes were intron-rich and conserved in gene structure, and they coded for proteins with a nucleoplasmin-like (NPL) domain. Expression analysis showed that B. napus, B. rapa, and B. oleracea HDT genes were expressed in different organs at different developmental stages, while different HDT subgroups were specifically expressed in specific organs and tissues. Interestingly, most of the Bna/Br/BoHDT2 members were expressed in flowers, buds and siliques, suggesting they have an important role in the development of reproductive organs in Brassicaceae. Expression of BnaHDT was induced by various hormones, such as ABA and ethylene treatment, and some subgroups of genes were responsive to heat treatment. The expression of most HDT members was strongly induced by cold stress and freezing stress after non-cold acclimation, while it was slightly induced after cold acclimation. In this study, the HDT gene family of Brassicaceae was analyzed for the first time, which helps in understanding the function of BnaHDT in regulating plant responses to abiotic stresses, especially freezing stresses.

The Role of ABA in the Interaction between Citrus Fruit and Penicillium digitatum

Abscisic acid (ABA) protects citrus fruit against Penicillium digitatum infection. The global mechanisms involved in the role of ABA in the P. digitatum-citrus fruit interaction are unknown. Here, we determine the transcriptome differences between the Navelate (Citrus sinensis (L.) Osbeck) orange and its ABA-deficient mutant Pinalate, which is less resistant to infection. Low ABA levels may affect both the constitutive mechanisms that protect citrus fruit against P. digitatum and early responses to infection. The repression of terpenoid, phenylpropanoid and glutation metabolism; of oxidation-reduction processes; and of processes related to the defense response to fungus and plant hormone signal transduction may be one part of the constitutive defense reduced in the mutant against P. digitatum. Our results also provide potential targets for developing P. digitatum-citrus fruit-resistant varieties. Of those up-regulated by ABA, a thaumatin protein and a bifunctional inhibitor/LTP, which are relevant in plant immunity, were particularly remarkable. It is also worth highlighting chlorophyllase 1 (CLH1), induced by infection in Pinalate, and the OXS3 gene, which was down-regulated by ABA, because the absence of OXS3 activates ABA-responsive genes in plants.

Genomic Characteristics of Elite Maize Inbred Line 18-599 and Its Transcriptional Response to Drought and Low-Temperature Stresses

Elite inbred line 18-599 was developed via triple test cross from introduced hybrid P78599 and used as parents of dozens of maize hybrids adapting to the diverse ecological conditions of the maize ecological region in Southwest China. In this study, its genomic DNA was resequenced and aligned with the B73 genome sequence to identify single nucleotide polymorphism (SNP), and insertion (In) and deletion (Del) loci. These loci were aligned with those between B73 and 1020 inbred lines in the HapMap database to identify specific variation loci of 18-599. The results showed that there were 930,439 specific SNPs and 358,750 InDels between 18-599 and the 1020 lines. In total, 21,961 of them showed significant impacts on the functions of 12,297 genes, such as frameshift, change of splicing site, stop gain, change of start site, and stop loss. Phylogenetic analysis showed that 18-599 was closely related to inbred lines ZEAxujRAUDIAAPE and 2005-4, but far from some inbred lines directly isolated from P78599. This result indicated that 18-599 not only pyramided the elite genes of P78599, but also acquired genetic divergence during the repetitive backcrosses of triple test cross to confer its elite agronomic characteristics. Subsequently, the RNA of 18-599 was sequenced. The aligned 9713 and 37,528 of the 165,098 unigenes were screened and aligned with annotated transcripts of the B73 genome differentially expressed under drought and low-temperature stress, respectively, and their functions were involved in the responses to these stresses. The quantitative PCR results of fourteen random genes verified the RNA sequencing results. These findings suggest that the transcriptional responses of many resistance-related genes were an important mechanism for 18-599 to adapt to diverse ecological conditions.

A critical review on plant annexin: Structure, function, and mechanism

Plant annexins are evolutionary conserved protein family widely exist in almost all plant species, characterized by a shorter N-terminal region and four conservative annexin repeats. Plant annexins have Ca²⁺ channel-regulating activity and peroxidase as well as ATPase/GTPase activities, which give annexins functional specificity. They are widely involved in regulating diverse aspects of biochemical and cellular processes, plant growth and development, and responses to biotic and abiotic environmental stresses. Though many studies have reviewed the function of annexins, great progress have been made in the study of plant annexins recently. In this review, we outline the current understanding of basic properties of plant annexins and summarize the emerging advances in understanding the functional roles of annexins in plants and highlight the regulation mechanisms of annexin protein in response to stress especially to salt and cold stress. The interesting questions related to plant annexin that remain to be further elucidated are also discussed.

Morphological, physiological and molecular assessment of cotton for drought tolerance under field conditions

Climate change could be an existential threat to many crops. Drought and heat stress are becoming harder for cultivated crops. Cotton in Pakistan is grown under natural high temperature and low moisture, could be used as a source of heat and drought tolerance. Therefore, the study was conducted to morphological, physiological and molecular characterization of cotton genotypes under field conditions. A total of 25 cotton genotypes were selected from the gene pool of Pakistan based on tolerance to heat and drought stress. In field trail, the stress related traits like boll retention percentage, plant height, number of nodes and inter-nodal distance were recorded. In physiological assessment, traits such as photosynthesis rate, stomatal conductance, transpiration rate, leaf temperature, relative water content and excised leaf water loss were observed. At molecular level, a set of 19 important transcription factors, controlling drought/heat stress tolerance (HSPCB, GHSP26, HSFA2, HSP101, HSP3, DREB1A, DREB2A, TPS, GhNAC2, GbMYB5, GhWRKY41, GhMKK3, GhMPK17, GhMKK1, GhMPK2, APX1, HSC70, ANNAT8, and GhPP2A1) were analyzed from all genotypes. Data analyses depicted that boll retention percentage, photosynthesis, stomatal conductance, relative water content under the stress conditions were associated with the presence of important drought & heat TF/genes which depicts high genetic potential of Pakistani cotton varieties against abiotic stress. The variety MNH-886 appeared in medium plant height, high boll retention percentage, high relative water content, photosynthesis rate, stomatal conductance, transpiration rate and with maximum number transcription factors under study. The variety may be used as source material for heat and drought tolerant cotton breeding. The results of this study may be useful for the cotton breeders to develop genotype adoptable to environmental stresses under climate change scenario.

Arabidopsis annexin 5 is involved in maintenance of pollen membrane integrity and permeability

In Arabidopsis, a dry stigma surface enables a gradual hydration of pollen grains by a controlled release of water. Occasionally the grains may be exposed to extreme precipitations that cause rapid water influx and swelling, eventually leading to pollen membrane rupture. In metazoans, calcium- and phospholipid-binding proteins, referred to as annexins, participate in the repair of plasma membrane damages. It remains unclear, however, how this process is conducted in plants. Here, we examined whether plant annexin 5 (ANN5), the most abundant member of the annexin family in pollen, is involved in the restoration of pollen membrane integrity. We analyzed the cellular dynamics of ANN5 in pollen grains undergoing hydration in favorable or stress conditions. We observed a transient association of ANN5 with the pollen membrane during in vitro hydration that did not occur in the pollen grains being hydrated on the stigma. To simulate a rainfall, we performed spraying of the pollinated stigma with deionized water that induced ANN5 accumulation at the pollen membrane. Interestingly, calcium or magnesium application affected pollen membrane properties differently, causing rupture or shrinkage of pollen membrane, respectively. Both treatments, however, induced ANN5 recruitment to the pollen membrane. Our data suggest a model in which ANN5 is involved in the maintenance of membrane integrity in pollen grains exposed to osmotic or ionic imbalances.

Identification of WRKY transcription factors responding to abiotic stresses in Brassica napus L

A total of 278 BnWRKYs were identified and analyzed. Ectopic expression of BnWRKY149 and BnWRKY217 suggests that they function in the ABA signaling pathway. WRKY transcription factors play an important role in plant development, however, their function in Brassica napus L. abiotic stress response is still unclear. In this study, a total of 278 BnWRKY transcription factors were identified from the B. napus genome data, and they were subsequently distributed in three main groups. The protein motifs and classification of BnWRKY transcription factors were analyzed, and the locations of their corresponding encoding genes were mapped on the chromosomes of B. napus. Transcriptome analysis of rapeseed seedlings exposed to drought, salt, heat, cold and abscisic acid treatment revealed that 99 BnWRKYs responded to at least one of these stresses. The expression profiles of 12 BnWRKYs were examined with qPCR and the result coincided with RNA-seq analysis. Two genes of interest, BnWRKY149 and BnWRKY217 (homologs of AtWRKY40), were overexpressed in Arabidopsis, and the corresponding proteins were located to the nucleus. Transgene plants of BnWRKY149 and BnWRKY217 were less sensitive to ABA than Arabidopsis Col-0 plants, suggesting they might play important roles in the responses of rapeseed to abiotic stress.

The evolution of the expansin gene family in Brassica species

Expansin gene (EXP) family plays important roles in plant growth and crop improvement. However, it has not been well studied in the Brassica genus that includes several important agricultural and horticultural crops. To get insight to the evolution and expansion of EXP family in Brassica, Brassica EXPs which are homologues of 35 known AtEXPs of Arabidopsis were comprehensively and systematically analyzed in the present study. In total, 340 Brassica EXPs were clustered into four groups that corresponded multiple alignment to four subfamilies of AtEXPs, with divergent conserved motifs and cis-acting elements among groups. To understand the expansion of EXP family, an integrated genomic block system was constructed among Arabidopsis and Brassica species based on 24 known ancestral karyotype blocks. Obvious gene loss, segmental duplication, tandem duplication and DNA sequence repeat events were found during the expansion of Brassica EXPs, of which the segmental duplication was possibly the major driving force. The divergence time was estimated in 1109 orthologs pairs of EXPs, revealing the divergence of Brassica EXPs from AtEXPs during ~30 MYA, and the divergence of EXPs among Brassica species during 13.50-17.94 MYA. Selective mode analysis revealed that the purifying selection was the major contributor to expansion of Brassica EXPs. This study provides new insights into the evolution and expansion of the EXP family in Brassica genus.

The Same against Many: AtCML8, a Ca2+ Sensor Acting as a Positive Regulator of Defense Responses against Several Plant Pathogens

Calcium signals are crucial for the activation and coordination of signaling cascades leading to the establishment of plant defense mechanisms. Here, we studied the contribution of CML8, an Arabidopsis calmodulin-like protein in response to Ralstonia solanacearum and to pathogens with different lifestyles, such as Xanthomonas campestris pv. campestris and Phytophtora capsici. We used pathogenic infection assays, gene expression, RNA-seq approaches, and comparative analysis of public data on CML8 knockdown and overexpressing Arabidopsis lines to demonstrate that CML8 contributes to defense mechanisms against pathogenic bacteria and oomycetes. CML8 gene expression is finely regulated at the root level and manipulated during infection with Ralstonia, and CML8 overexpression confers better plant tolerance. To understand the processes controlled by CML8, genes differentially expressed at the root level in the first hours of infection have been identified. Overexpression of CML8 also confers better tolerance against Xanthomonas and Phytophtora, and most of the genes differentially expressed in response to Ralstonia are differentially expressed in these different pathosystems. Collectively, CML8 acts as a positive regulator against Ralstonia solanaceraum and against other vascular or root pathogens, suggesting that CML8 is a multifunctional protein that regulates common downstream processes involved in the defense response of plants to several pathogens.

Characterization of Annexin gene family and functional analysis of RsANN1a involved in heat tolerance in radish (Raphanus sativus L.)

Plant annexins are a kind of conserved Ca²⁺-dependent phospholipid-binding proteins which are involved in plant growth, development and stress tolerance. Radish is an economically important annual or biennial root vegetable crop worldwide. However, the genome-wide characterization of annexin (RsANN) gene family remain largely unexplored in radish. In this study, a comprehensive identification of annexin gene family was performed at the whole genome level in radish. In total, ten RsANN genes were identified, and these putative RsANN proteins shared typical characteristics of the annexin family proteins. Phylogenetic analysis showed that the RsANNs together with annexin from Arabidopsis and rice were clustered into five groups with shared similar motif patterns. Chromosomal localization showed that these ten RsANN genes were distributed on six chromosomes (R3-R8) of radish. Several cis-elements involved in abiotic stress response were identified in the promoter regions of RsANN genes. Expression profile analysis indicated that the RsANN genes exhibited tissue-specific patterns at different growth stages and tissues. The Real-time quantitative PCR (RT-qPCR) revealed that the expression of most RsANN genes was induced under various abiotic stresses including heat, drought, salinity, oxidization and ABA stress. In addition, stress assays showed that overexpression of RsANN1a improved plant's growth and heat tolerance, while artificial microRNAs (amiRNA)-mediated knockdown of RsANN1a caused dramatically decreased survival ratio of Arabidopsis plants. These findings not only demonstrate that RsANN1a might play a critical role in the heat stress response of radish, but also facilitate clarifying the molecular mechanism of RsANN genes in regulating the biological process governing plant growth and development.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01056-5.

Genome-Wide Identification and Transcriptional Expression Analysis of Annexin Genes in Capsicum annuum and Characterization of CaAnn9 in Salt Tolerance

Annexin (Ann) is a polygenic, evolutionarily conserved, calcium-dependent and phospholipid-binding protein family, which plays key roles in plant growth, development, and stress response. However, a comprehensive understanding of CaAnn genes of pepper (Capsicum annuum) at the genome-wide level is limited. Based on the available pepper genomic information, we identified 15 members of the CaAnn gene family. Phylogenetic analysis showed that CaAnn proteins could be categorized into four different orthologous groups. Real time quantitative RT-PCR analysis showed that the CaAnn genes were tissue-specific and were widely expressed in pepper leaves after treatments with cold, salt, and drought, as well as exogenously applied MeJA and ABA. In addition, the function of CaAnn9 was further explored using the virus-induced gene silencing (VIGS) technique. CaAnn9-silenced pepper seedlings were more sensitive to salt stress, reflected by the degradation of chlorophyll, the accumulation of reactive oxygen species (ROS), and the decrease of antioxidant defense capacity. This study provides important information for further study of the role of pepper CaAnn genes and their coding proteins in growth, development, and environmental responses.

Genome-wide identification and expression pattern analysis of lipoxygenase gene family in banana

The LOX genes have been identified and characterized in many plant species, but studies on the banana LOX genes are very limited. In this study, we respectively identified 18 MaLOX, 11 MbLOX, and 12 MiLOX genes from the Musa acuminata, M. balbisiana and M. itinerans genome data, investigated their gene structures and characterized the physicochemical properties of their encoded proteins. Banana LOXs showed a preference for using and ending with G/C and their encoded proteins can be classified into 9-LOX, Type I 13-LOX and Type II 13-LOX subfamilies. The expansion of the MaLOXs might result from the combined actions of genome-wide, tandem, and segmental duplications. However, tandem and segmental duplications contribute to the expansion of MbLOXs. Transcriptome data based gene expression analysis showed that MaLOX1, 4, and 7 were highly expressed in fruit and their expression levels were significantly regulated by ethylene. And 11, 12 and 7 MaLOXs were found to be low temperature-, high temperature-, and Fusarium oxysporum f. sp. Cubense tropical race 4 (FocTR4)-responsive, respectively. MaLOX8, 9 and 13 are responsive to all the three stresses, MaLOX4 and MaLOX12 are high temperature- and FocTR4-responsive; MaLOX6 and MaLOX17 are significantly induced by low temperature and FocTR4; and the expression of MaLOX7 and MaLOX16 are only affected by high temperature. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression levels of several MaLOXs are regulated by MeJA and FocTR4, indicating that they can increase the resistance of banana by regulating the JA pathway. Additionally, the weighted gene co-expression network analysis (WGCNA) of MaLOXs revealed 3 models respectively for 5 (MaLOX7-11), 3 (MaLOX6, 13, and 17), and 1 (MaLOX12) MaLOX genes. Our findings can provide valuable information for the characterization, evolution, diversity and functionality of MaLOX, MbLOX and MiLOX genes and are helpful for understanding the roles of LOXs in banana growth and development and adaptations to different stresses.

Mechanisms of specific systemic response in wheat plants under different locally acting heat stimuli

Mechanisms of the specific systemic response of plant to different adverse factors are poorly understood. We studied the mechanisms acting in wheat (Triticum aestivum L.) under the action of local burn and gradual heating. Both stimuli induce a variation potential (VP) propagation and a biphasic (fast and long-term phases) photosynthetic response in non-stimulated zones of plant with stimulus-specific parameters of the latter: the fast phase or long-term phase predominance in responses induced by burn or heating, respectively. The burn-induced VP and photosynthetic response attenuate with distance, while the heating-induced VP and photosynthetic response were of more stable amplitude in distant part of the stimulated plant. VP propagation in both cases induced apoplast alkalization with dynamics well corresponding to such of VP and of the fast phase of photosynthetic response. Gradual heating induced a significant rise in jasmonate production along with a decrease in stomatal conductance with characteristic times well corresponding to the long-term phase of the photosynthetic response. We suppose that the VP-induced pH shift is responsible for in the induction of the fast phase, while jasmonate production for the long-term phase of the photosynthetic response. The revealed differences in the systemic response to stressors studied, apparently, reflect two distinct plant adaptation strategies to fast and slow-growing stimuli. The immediate response in the tissue nearest to the damage zone is the most important under a fast-growing stimulus. The fundamentally different situation is under a slowly-growing stimulus which provokes long-term changes in the plant that ensure the preparation of the whole organism for impending environmental changes.

Targeting salt stress coping mechanisms for stress tolerance in Brassica: A research perspective

Brassica genus comprises numerous cultivated brassica species with various economic importance. Salt stress is an overwhelming problem causing serious losses in Brassica species (e.g. B. napus, B. rapa, B. oleracea, B. juncea) growth and grain yield production by inducing ionic and ROS toxicity. Given that a significant variation exists in salt tolerance level in Brassica genus, Brassica species exhibited numerous salt tolerance mechanisms which were either overlooked or given less importance to improve and understand innate salt stress tolerance mechanism in Brassica species. In this review, we tried to highlight the importance and recent findings relating to some overlooked and potential mechanisms such as role of neurotransmitters, and role of cytosolic Ca²⁺ and ROS as signaling elements to enhance salt stress tolerance. Studies revealed that salt tolerant brassica species retained more K⁺ in leaf mesophyll which confers overall salinity tolerance in salt tolerance brassica species. Neurotransmitter such as melatonin, dopamiane and eATP regulates K⁺ and Ca²⁺ permeable ion channels and plays a very crucial role in ionic homeostasis under salinity stress in brassica. At the end, the numerous possible salt stress agronomic strategies were also discussed to mitigate the severity of the salt stress in Brassica species.

Genome-wide identification and expression analysis of CaM/CML genes in Brassica napus under abiotic stress

Calmodulin (CaM) and calmodulin-like (CML) proteins are primary calcium (Ca²⁺) sensors and are involved in the regulation of plant development and stress responses by converting calcium signals into transcriptional responses, protein phosphorylation, or metabolic changes. However, the characterization and expression profiling of CaM/CML genes in Brassica napus remain limited. The present study reports that 25 BnaCaM and 168 BnaCML genes were identified in B. napus. The phylogenetics, gene structures, gene motifs, gene chromosomal locations, syntenic and Ka/Ks analysis, promoter cis-acting elements, and expression characteristics in various organs and under abiotic stress were evaluated. The phylogenetic results revealed a total of 11 subgroups, including one unique clade of CaMs distinct from CMLs. Most of group I (CaM), II, III, and X members are intron rich, while members from the other seven groups are intron-less. The majority of CaM/CML proteins have four EF-hands. Syntenic analysis showed that 91.3 % orthologous CaM/CML gene pairs between B. rapa and B. oleracea were retained as homologous gene pairs in B. napus. Ka/Ks analysis indicated that the majority of BnaCaM/CML experienced purifying selection. Expression analysis showed that BnaCaMs genes are highly and ubiquitously expressed in all of the organs and tissues examined, while distinct BnaCMLs are expressed specifically in particular organs and tissues. In total, 129 BnaCaM/CML were induced by abiotic stress and phytohormones. BnaCMLs from group IV, VI, VIII, and X were strongly induced by freezing treatment, but were not or just slightly induced by chilling treatment. The present study is the first to analyze the CaM/CML gene family in B. napus, which is useful for understanding the functions of the BnaCaM/CML in modulating plant responses to abiotic stress, especially freezing stress.

Advanced Microscopy Reveals Complex Developmental and Subcellular Localization Patterns of ANNEXIN 1 in Arabidopsis

Annexin 1 (ANN1) is the most abundant member of the evolutionary conserved multigene protein superfamily of annexins in plants. Generally, annexins participate in diverse cellular processes, such as cell growth, differentiation, vesicle trafficking, and stress responses. The expression of annexins is developmentally regulated, and it is sensitive to the external environment. ANN1 is expressed in almost all Arabidopsis tissues, while the most abundant is in the root, root hairs, and in the hypocotyl epidermal cells. Annexins were also occasionally proposed to associate with cytoskeleton and vesicles, but they were never developmentally localized at the subcellular level in diverse plant tissues and organs. Using advanced light-sheet fluorescence microscopy (LSFM), we followed the developmental and subcellular localization of GFP-tagged ANN1 in post-embryonic Arabidopsis organs. By contrast to conventional microscopy, LSFM allowed long-term imaging of ANN1-GFP in Arabidopsis plants at near-environmental conditions without affecting plant viability. We studied developmental regulation of ANN1-GFP expression and localization in growing Arabidopsis roots: strong accumulation was found in the root cap and epidermal cells (preferentially in elongating trichoblasts), but it was depleted in dividing cells localized in deeper layers of the root meristem. During root hair development, ANN1-GFP accumulated at the tips of emerging and growing root hairs, which was accompanied by decreased abundance in the trichoblasts. In aerial plant parts, ANN1-GFP was localized mainly in the cortical cytoplasm of trichomes and epidermal cells of hypocotyls, cotyledons, true leaves, and their petioles. At the subcellular level, ANN1-GFP was enriched at the plasma membrane (PM) and vesicles of non-dividing cells and in mitotic and cytokinetic microtubular arrays of dividing cells. Additionally, an independent immunolocalization method confirmed ANN1-GFP association with mitotic and cytokinetic microtubules (PPBs and phragmoplasts) in dividing cells of the lateral root cap. Lattice LSFM revealed subcellular accumulation of ANN1-GFP around the nuclear envelope of elongating trichoblasts. Massive relocation and accumulation of ANN1-GFP at the PM and in Hechtian strands and reticulum in plasmolyzed cells suggest a possible osmoprotective role of ANN1-GFP during plasmolysis/deplasmolysis cycle. This study shows complex developmental and subcellular localization patterns of ANN1 in living Arabidopsis plants.