Identification of CBL and CIPK gene families and functional characterization of CaCIPK1 under Phytophthora capsici in pepper (Capsicum annuum L.)

AtCIPK20 regulates microtubule stability to mediate stomatal closure under drought stress in Arabidopsis

Drought stress is a common abiotic challenge that profoundly impacts plant growth and development. As sessile organisms, plants rely on various physiological and morphological adaptations to cope with drought conditions. The CIPK (calcineurin B-like protein-interacting protein kinase) family proteins play a pivotal role in mediating plant responses to abiotic stress through modulation of cellular membrane events via the CBL-CIPK complex. However, reports documenting the CIPKs' regulation of non-membrane events are scant. In this study, we discovered a novel subcellular localisation pattern of the AtCIPK20 protein of Arabidopsis, specifically to cortical microtubules (cMT), which is distinct from previously reported localisation patterns of plant CIPKs. AtCIPK20 regulates ABA-induced loss of cMT organisation in guard cells, thereby facilitating stomatal closure, mitigating leaf water loss, and protecting plants from drought stress in Arabidopsis. The C-terminal regulatory domain of AtCIPK20 governs its cMT targeting, whereas the interaction of AtCIPK20 with its CBL partners disrupts this localisation. Notably, the cMT targeting characteristic of AtCIPK20 is not exclusive, as several other CIPK members in Arabidopsis, maize, and rice exhibit similar localisation patterns. These findings broaden our current understanding of the role of plant CIPK members in abiotic stress resistance and suggest that future exploration of CIPK molecular functions should adopt a more comprehensive perspective.

A conserved oomycete effector RxLR23 triggers plant defense responses by targeting ERD15La to release NbNAC68

Oomycete pathogens deliver many effectors to enhance virulence or suppress plant immunity. Plant immune networks are interconnected, in which a few effectors can trigger a strong defense response when recognized by immunity-related proteins. How effectors activate plant defense response remains poorly understood. Here we report Phytophthora capsici effector RxLR23KM can induce plant cell death and plant immunity. RxLR23KM specifically binds to ERD15La, a regulator of abscisic acid and salicylic acid pathway, and the binding intensity depends on the amino acid residues (K93 and M320). NbNAC68, a downstream protein of ERD15La, can stimulate plant immunity that is compromised after binding with ERD15La. Silencing of NbNAC68 substantially prevents the activation of plant defense response. RxLR23KM binds to ERD15La, releasing NbNAC68 to activate plant immunity. These findings highlight a strategy of plant defense response that ERD15La as a central regulator coordinates RxLR23KM to regulate NbNAC68-triggered plant immunity.

Genome-Wide Identification of Members of the Soybean CBL Gene Family and Characterization of the Functional Role of GmCBL1 in Responses to Saline and Alkaline Stress

Calcium ions function as key messengers in the context of intracellular signal transduction. The ability of plants to respond to biotic and abiotic stressors is highly dependent on the calcineurin B-like protein (CBL) and CBL-interacting protein kinase (CIPK) signaling network. Here, a comprehensive effort was made to identify all members of the soybean CBL gene family, leading to the identification of 15 total genes distributed randomly across nine chromosomes, including 13 segmental duplicates. All the GmCBL gene subfamilies presented with similar gene structures and conserved motifs. Analyses of the expression of these genes in different tissues revealed that the majority of these GmCBLs were predominantly expressed in the roots. Significant GmCBL expression and activity increases were also observed in response to a range of stress-related treatments, including salt stress, alkaline stress, osmotic stress, or exposure to salicylic acid, brassinosteroids, or abscisic acid. Striking increases in GmCBL1 expression were observed in response to alkaline and salt stress. Subsequent analyses revealed that GmCBL1 was capable of enhancing soybean salt and alkali tolerance through the regulation of redox reactions. These results offer new insight into the complex mechanisms through which the soybean CBL gene family regulates the responses of these plants to environmental stressors, highlighting promising targets for efforts aimed at enhancing soybean stress tolerance.

The role of CBL-CIPK signaling in plant responses to biotic and abiotic stresses

Plants have a variety of regulatory mechanisms to perceive, transduce, and respond to biotic and abiotic stress. One such mechanism is the calcium-sensing CBL-CIPK system responsible for the sensing of specific stressors, such as drought or pathogens. CBLs perceive and bind Calcium (Ca2+) in response to stress and then interact with CIPKs to form an activated complex. This leads to the phosphorylation of downstream targets, including transporters and ion channels, and modulates transcription factor levels and the consequent levels of stress-associated genes. This review describes the mechanisms underlying the response of the CBL-CIPK pathway to biotic and abiotic stresses, including regulating ion transport channels, coordinating plant hormone signal transduction, and pathways related to ROS signaling. Investigation of the function of the CBL-CIPK pathway is important for understanding plant stress tolerance and provides a promising avenue for molecular breeding.

Molecular Mechanisms of CBL-CIPK Signaling Pathway in Plant Abiotic Stress Tolerance and Hormone Crosstalk

Abiotic stressors, including drought, salt, cold, and heat, profoundly impact plant growth and development, forcing elaborate cellular responses for adaptation and resilience. Among the crucial orchestrators of these responses is the CBL-CIPK pathway, comprising calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs). While CIPKs act as serine/threonine protein kinases, transmitting calcium signals, CBLs function as calcium sensors, influencing the plant's response to abiotic stress. This review explores the intricate interactions between the CBL-CIPK pathway and plant hormones such as ABA, auxin, ethylene, and jasmonic acid (JA). It highlights their role in fine-tuning stress responses for optimal survival and acclimatization. Building on previous studies that demonstrated the enhanced stress tolerance achieved by upregulating CBL and CIPK genes, we explore the regulatory mechanisms involving post-translational modifications and protein-protein interactions. Despite significant contributions from prior research, gaps persist in understanding the nuanced interplay between the CBL-CIPK system and plant hormone signaling under diverse abiotic stress conditions. In contrast to broader perspectives, our review focuses on the interaction of the pathway with crucial plant hormones and its implications for genetic engineering interventions to enhance crop stress resilience. This specialized perspective aims to contribute novel insights to advance our understanding of the potential of the CBL-CIPK pathway to mitigate crops' abiotic stress.

Genome-wide identification, expression analysis, and abiotic stress response of the CBL and CIPK gene families in Artocarpus nanchuanensis

Artocarpus nanchuanensis, the northernmost species in the jackfruit genus, has great economic and horticultural value due to its nutritious fruit and beautiful tree shape. Calcineurin B-like proteins (CBLs) act as plant-specific Ca2+ sensors and participate in regulating plant responses to various abiotic stresses by interacting with CBL-interacting protein kinases (CIPKs). However, the characteristics and functions of the CBL and CIPK genes in A. nanchuanensis are still unclear. Here, we identified 14 CBL and 33 CIPK genes from the A. nanchuanensis genome, and based on phylogenetic analysis, they were divided into 4 and 7 clades, respectively. Gene structure and motif analysis indicated that the AnCBL and AnCIPK genes were relatively conserved. Colinear analysis showed that segmental duplication contributed to the expansion of the AnCBL and AnCIPK gene families. Expression analysis showed that AnCBL and AnCIPK genes were widely expressed in various tissues of A. nanchuanensis and exhibited tissue-specific expression. In addition, three genes (AnCBL6, AnCIPK7/8) may play important roles in response to salt, cold, and drought stresses. In summary, this study lays an important foundation for the improvement of stress resistance in A. nanchuanensis and provides new insight for the functional research on CBL and CIPK gene families.

Unveiling molecular mechanisms of pepper resistance to Phytophthora capsici through grafting using iTRAQ-based proteomic analysis

Phytophthora blight severely threatens global pepper production. Grafting bolsters plant disease resistance, but the underlying molecular mechanisms remain unclear. In this study, we used P. capsici-resistant strain 'ZCM334' and susceptible strain 'Early Calwonder' for grafting. Compared to self-rooted 'Early Calwonder' plants, 'ZCM334' grafts exhibited delayed disease onset, elevated resistance, and reduced leaf cell damage, showcasing the potential of grafting in enhancing pepper resistance to P. capsici. Proteomic analysis via the iTRAQ technology unveiled 478 and 349 differentially expressed proteins (DEPs) in the leaves and roots, respectively, between the grafts and self-rooted plants. These DEPs were linked to metabolism and cellular processes, stimulus responses, and catalytic activity and were significantly enriched in the biosynthesis of secondary metabolites, carbon fixation in photosynthetic organizations, and pyruvate metabolism pathways. Twelve DEPs exhibiting consistent expression trends in both leaves and roots, including seven related to P. capsici resistance, were screened. qRT-PCR analysis confirmed a significant correlation between the protein and transcript levels of DEPs after P. capsici inoculation. This study highlights the molecular mechanisms whereby grafting enhances pepper resistance to Phytophthora blight. Identification of key genes provides a foundation for studying the regulatory network governing the resistance of pepper to P. capsici.

Knockout of SlbZIP68 reduces late blight resistance in tomato

Tomato (Solanum lycopersicum) is one of the most widely cultivated vegetable crop species in the world. Tomato late blight caused by Phytophthora infestans is a severe disease, which can cause serious losses in tomato production. In this study, tomato SlbZIP68 was identified as a transcription factor that can be induced by P. infestans, salicylic acid (SA) and jasmonic acid (JA). Knockout of SlbZIP68 via clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) technology revealed a significant decrease in tomato resistance to P. infestans. Furthermore, knockout of SlbZIP68 reduced the activity of defense enzymes and increased the accumulation of reactive oxygen species (ROS). Our findings also indicated that SlbZIP68 can activate the expression of the PR genes and enhance resistance to P. infestans. In addition, SlbZIP68 can bind to the PR3 and PR5 promoters and induce gene expression, as revealed by yeast one-hybrid (Y1H) and dual-luciferase (LUC) assays. These findings not only elucidate the mechanisms of response to P. infestans but also enable targeted breeding strategies for tomato resistance to P. infestans.

The calcium connection: exploring the intricacies of calcium signaling in plant-microbe interactions

The process of plant immune response is orchestrated by intracellular signaling molecules. Since plants are devoid of a humoral system, they develop extensive mechanism of pathogen recognition, signal perception, and intricate cell signaling for their protection from biotic and abiotic stresses. The pathogenic attack induces calcium ion accumulation in the plant cells, resulting in calcium signatures that regulate the synthesis of proteins of defense system. These calcium signatures induct different calcium dependent proteins such as calmodulins (CaMs), calcineurin B-like proteins (CBLs), calcium-dependent protein kinases (CDPKs) and other signaling molecules to orchestrate the complex defense signaling. Using advanced biotechnological tools, the role of Ca2+ signaling during plant-microbe interactions and the role of CaM/CMLs and CDPKs in plant defense mechanism has been revealed to some extent. The Emerging perspectives on calcium signaling in plant-microbe interactions suggest that this complex interplay could be harnessed to improve plant resistance against pathogenic microbes. We present here an overview of current understanding in calcium signatures during plant-microbe interaction so as to imbibe a future direction of research.

Potato calcineurin B-like protein CBL4, interacting with calcineurin B-like protein-interacting protein kinase CIPK2, positively regulates plant resistance to stem canker caused by Rhizoctonia solani

Introduction

Calcium sensor calcineurin B-like proteins (CBLs) and their interacting partners, CBL-interacting protein kinases (CIPKs), have emerged as a complex network in response to abiotic and biotic stress perception. However, little is known about how CBL-CIPK complexes function in potatoes.

Methods

In this study, we identified the components of one potato signaling complex, StCBL4-StCIPK2, and characterized its function in defense against Rhizoctonia solani causing stem canker in potato.

Results

Expressions of both StCBL4 and StCIPK2 from potato were coordinately induced upon R. solani infection and following exposure to the defense genes. Furthermore, transient overexpression of StCBL4 and StCIPK2 individually and synergistically increased the tolerance of potato plants to R. solani in Nicotiana benthamiana. Additionally, the transgenic potato has also been shown to enhance resistance significantly. In contrast, susceptibility to R. solani was exhibited in N. benthamiana following virus-induced gene silencing of NbCBL and NbCIPK2. Evidence revealed that StCBL4 could interact in yeast and in planta with StCIPK2. StCBL4 and StCIPK2 transcription was induced upon R. solani infection and this expression in response to the pathogen was enhanced in StCBL4- and StCIPK2-transgenic potato. Moreover, accumulated expression of pathogenesis-related (PR) genes and reactive oxygen species (ROS) was significantly upregulated and enhanced in both StCBL4- and StCIPK2- transgenic potato.

Discussion

Accordingly, StCBL4 and StCIPK2 were involved in regulating the immune response to defend the potato plant against R. solani. Together, our data demonstrate that StCBL4 functions in concert with StCIPK2, as positive regulators of immunity, contributing to combating stem canker disease in potato.

Screening of Candidate Genes Associated with Brown Stripe Resistance in Sugarcane via BSR-seq Analysis

Sugarcane brown stripe (SBS), caused by the fungal pathogen Helminthosporium stenospilum, is one of the most serious threats to sugarcane production. However, its outbreaks and epidemics require suitable climatic conditions, resulting in the inefficient improvement of the SBS resistance by phenotype selection. The sugarcane F1 population of SBS-resistant YT93-159 × SBS-susceptible ROC22 was used for constructing the bulks. Bulked segregant RNA-seq (BSR-seq) was then performed on the parents YT93-159 (T01) and ROC22 (T02), and the opposite bulks of 30 SBS-susceptible individuals mixed bulk (T03) and 30 SBS-resistant individuals mixed bulk (T04) collected from 287 F1 individuals. A total of 170.00 Gb of clean data containing 297,921 SNPs and 70,426 genes were obtained. Differentially expressed genes (DEGs) analysis suggested that 7787 and 5911 DEGs were identified in the parents (T01 vs. T02) and two mixed bulks (T03 vs. T04), respectively. In addition, 25,363 high-quality and credible SNPs were obtained using the genome analysis toolkit GATK for SNP calling. Subsequently, six candidate regions with a total length of 8.72 Mb, which were located in the chromosomes 4B and 7C of sugarcane wild species Saccharum spontaneum, were identified, and 279 genes associated with SBS-resistance were annotated by ED algorithm and ΔSNP-index. Furthermore, the expression profiles of candidate genes were verified by quantitative real-time PCR (qRT-PCR) analysis, and the results showed that eight genes (LRR-RLK, DHAR1, WRKY7, RLK1, BLH4, AK3, CRK34, and NDA2) and seven genes (WRKY31, CIPK2, CKA1, CDPK6, PFK4, CBL2, and PR2) of the 20 tested genes were significantly up-regulated in YT93-159 and ROC22, respectively. Finally, a potential molecular mechanism of sugarcane response to H. stenospilum infection is illustrate that the activations of ROS signaling, MAPK cascade signaling, Ca2+ signaling, ABA signaling, and the ASA-GSH cycle jointly promote the SBS resistance in sugarcane. This study provides abundant gene resources for the SBS resistance breeding in sugarcane.

Diverse roles of the CIPK gene family in transcription regulation and various biotic and abiotic stresses: A literature review and bibliometric study

CIPKs are a subclass of serine/threonine (Ser/Thr) protein kinases. CBLs are ubiquitous Ca2+ sensors that interact with CIPK with the aid of secondary Ca2+ messengers for regulation of growth and development and response to stresses faced by plants. The divergent roles of the CIPK-CBL interaction in plants include responding to environmental stresses (salt, cold, drought, pH, ABA signaling, and ion toxicity), ion homeostasis (K+, NH4 +, NO3 -, and microelement homeostasis), biotic stress, and plant development. Each member of this gene family produces distinct proteins that help plants adapt to diverse stresses or stimuli by interacting with calcium ion signals. CIPK consists of two structural domains-an N-terminal domain and a C-terminal domain-connected by a junction domain. The N-terminal domain, the site of phosphorylation, is also called the activation domain and kinase domain. The C-terminal, also known as the regulatory domain of CIPK, further comprises NAF/FISL and PPI. CBL comprises four EF domains and conserved PFPF motifs and is the site of binding with the NAF/FISL domain of CIPK to form a CBL-CIPK complex. In addition, we also performed a bibliometric analysis of the CIPK gene family of data extracted from the WoSCC. A total of 95 documents were retrieved, which had been published by 47 sources. The production over time was zigzagged. The top key terms were gene, CIPK, abiotic stress, and gene expression. Beijing Forestry University was the top affiliation, while The Plant Cell was the top source. The genomics and metabolomics of this gene family require more study.

Genome-wide identification of calcineurin B-like protein-interacting protein kinase gene family reveals members participating in abiotic stress in the ornamental woody plant Lagerstroemia indica

Calcineurin B-like protein-interacting protein kinases (CIPKs) play important roles in plant responses to stress. However, their function in the ornamental woody plant Lagerstroemia indica is remains unclear. In this study, the LiCIPK gene family was analyzed at the whole genome level. A total of 37 LiCIPKs, distributed across 17 chromosomes, were identified. Conserved motif analysis indicated that all LiCIPKs possess a protein kinase motif (S_TKc) and C-terminal regulatory motif (NAF), while seven LiCIPKs lack a protein phosphatase interaction (PPI) motif. 3D structure analysis further revealed that the N-terminal and C-terminal 3D-structure of 27 members are situated near to each other, while 4 members have a looser structure, and 6 members lack intact structures. The intra- and interspecies collinearity analysis, synonymous substitution rate (K _s ) peaks of duplicated LiCIPKs, revealed that ∼80% of LiCIPKs were retained by the two whole genome duplication (WGD) events that occurred approximately 56.12-61.16 million year ago (MYA) and 16.24-26.34 MYA ago. The promoter of each LiCIPK contains a number of auxin, abscisic acid, gibberellic acid, salicylic acid, and drought, anaerobic, defense, stress, and wound responsive cis-elements. Of the 21 members that were successfully amplified by qPCR, 18 LiCIPKs exhibited different expression patterns under NaCl, mannitol, PEG8000, and ABA treatments. Given that LiCIPK30, the AtSOS2 ortholog, responded to all four types of stress it was selected for functional verification. LiCIPK30 complements the atsos2 phenotype in vivo. 35S:LiCIPK-overexpressing lines exhibit increased leaf area increment, chlorophyll a and b content, reactive oxygen species scavenging enzyme activity, and expression of ABF3 and RD22, while the degree of membrane lipid oxidation decreases under NaCl treatment compared to WT. The evolutionary history, and potential mechanism by which LiCIPK30 may regulate plant tolerance to salt stress were also discussed. In summary, we identified LiCIPK members involved in abiotic stress and found that LiCIPK30 transgenic Arabidopsis exhibits more salt and osmotic stress tolerance than WT. This research provides a theoretical foundation for further investigation into the function of LiCIPKs, and for mining gene resources to facilitate the cultivation and breeding of new L. indica varieties in coastal saline-alkali soil.

Identification, expression, and association analysis of calcineurin B-like protein–interacting protein kinase genes in peanut

Plants usually respond to the external environment by initiating a series of signal transduction processes mediated by protein kinases, especially calcineurin B-like protein–interacting protein kinases (CIPKs). In this study, 54 CIPKs were identified in the peanut genome, of which 26 were from cultivated species (named AhCIPKs) and 28 from two diploid progenitors (Arachis duranensis—AdCIPKs and Arachis ipaensis—AiCIPKs). Evolution analysis revealed that the 54 CIPKs were composed of two different evolutionary branches. The CIPK members were unevenly distributed at different chromosomes. Synteny analysis strongly indicated that whole-genome duplication (allopolyploidization) contributed to the expansion of CIPK. Comparative genomics analysis showed that there was only one common collinear CIPK pairs among peanut, Arabidopsis, rice, grape, and soybean. The prediction results of cis-acting elements showed that AhCIPKs, AdCIPKs, and AiCIPKs contained different proportions of transcription factor binding motifs involved in regulating plant growth, abiotic stress, plant hormones, and light response elements. Spatial expression profiles revealed that almost all AhCIPKs had tissue-specific expression patterns. Furthermore, association analysis identified one polymorphic site in AdCIPK12 (AhCIPK11), which was significantly associated with pod length, seed length, hundred seed weight, and shoot root ratio. Our results provide valuable information of CIPKs in peanut and facilitate better understanding of their biological functions.

Evolution, gene expression, and protein‒protein interaction analyses identify candidate CBL-CIPK signalling networks implicated in stress responses to cold and bacterial infection in citrus

BACKGROUND

Cold is a major abiotic stress and Huanglongbing and citrus canker disease are two devastating bacterial diseases for citrus. The Ca²⁺-CBL-CIPK network is known to regulate different types of stress signalling in plants. How do CBL-CIPK signalling networks function in response to cold and infection by CLas or Xcc in citrus?

RESULTS

Eight calcineurin B-like proteins (CBLs) and seventeen CBL-interacting protein kinases (CIPKs) were identified from the cold-tolerant satsuma mandarin 'Guijing2501' (Citrus. unshiu) and CLas/Xcc-sensitive sweet orange (C. sinensis). Phylogenetic analysis revealed that both CBL and CIPK family members in citrus were classified into an ancient and a recent clade according to their conserved domain characteristics and/or intron/exon structures. Genome duplication analysis suggested that both tandem and segmental duplications contributed to the amplification of the CBL and CIPK gene families in citrus under intense purifying selection, and the duplication events only existed in the recent clades. Expression comparison of the duplicated gene pairs indicated that the duplicated CBL and CIPK genes underwent functional differentiation. Further expression analysis identified that CBL1, 5, 6, and 8 and CIPK2, 8, 12, 15, 16, and 17 were significantly regulated by multiple stresses, including cold, Xcc infection and/or CLas infection, in citrus, whereas CBL2/7 and CIPK1/4/5/11/13/14 were independently highly regulated by cold and CIPK3 was uniquely responsive to Xcc infection. The combination analyses of targeted Y2H assay and expression analysis revealed that CBL6-CIPK8 was the common signalling network in response to cold and Xcc infection, while CBL6/CBL8-CIPK14 was uniquely responsive to cold in citrus. Further stable transformation and cold tolerance assay indicated that overexpression of CuCIPK16 enhanced the cold tolerance of transgenic Arabidopsis with higher POD activity and lower MDA content.

CONCLUSIONS

In this study, evolution, gene expression and protein‒protein interaction analyses of citrus CBLs and CIPKs were comprehensively conducted over a genome-wide range. The results will facilitate future functional characterization of individual citrus CBLs and CIPKs under specific stresses and provide clues for the clarification of cold tolerance and disease susceptibility mechanisms in corresponding citrus cultivars.

The bHLH1-DTX35/DFR module regulates pollen fertility by promoting flavonoid biosynthesis in Capsicum annuum L

High pollen fertility can ensure the yield and efficiency of breeding work, but factors that affect the fertility of pepper pollen have not been studied extensively. In this work, we screened the reduced pollen fertility 1 (rpf1) mutant of Capsicum annuum with reduced pollen fertility and yellow anthers from an EMS (ethyl methanesulfonate)-mutagenized pepper population. Through construction of an F ₂ population followed by BSA (bulked segregant analysis) mapping and KASP genotyping, we identified CabHLH1 as a candidate gene for control of this trait. A G → A mutation at a splice acceptor site in CabHLH1 causes a frameshift mutation in the mutant, and the translated protein is terminated prematurely. Previous studies on CabHLH1 have focused on the regulation of flavonoid synthesis. Here, we found that CabHLH1 also has an important effect on pollen fertility. Pollen vigor, anther flavonoid content, and seed number were lower in CabHLH1-silenced pepper plants, whereas anther H₂O₂ and MDA (malondialdehyde) contents were higher. RNA-seq analyses showed that expression of the flavonoid synthesis genes DFR, ANS, and RT was significantly reduced in anthers of CabHLH1-silenced plants and rpf1 plants, as was the expression of DTX35, a gene related to pollen fertility and flavonoid transport. Yeast one-hybrid and dual-luciferase reporter assays showed that CabHLH1 can directly bind to the promoters of DTX35 and DFR and activate their expression. These results indicate that CabHLH1 regulates reactive oxygen species homeostasis by promoting the synthesis of anther flavonoids and acts as a positive regulator of pepper pollen fertility.

GmCIPK21, a CBL-interacting protein kinase confers salt tolerance in soybean (Glycine max. L)

Salt stress severely affects plant development and yield. Calcineurin B-like protein interacting protein kinases (CIPKs) play a crucial role in plant adaptation to environmental challenges. However, the biological functions of CIPKs in soybean remain poorly understood. Here, we identified GmCIPK21, a salt-responsive CIPK gene from soybean. Overexpression of GmCIPK21 in Arabidopsis and soybean hairy roots led to increased salt tolerance. The hairy roots with GmCIPK21 suppression by RNA interference exhibited salt-sensitive phenotypes. Further physiological analysis revealed that GmCIPK21 reduced the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and increased the activity of the antioxidant enzymes under salt stress. Additionally, GmCIPK21 was found to enhance the ABA sensitivity of transgenic plants. GmCIPK21 was also implicated in increasing the activation of antioxidant-, salt-, and ABA-related genes upon salt stress. Interestingly, GmCIPK21 interacted with GmCBL4, promoting the scavenging salt-induced reactive oxygen species (ROS). These results collectively suggested that GmCIPK21 affects ROS homeostasis and ABA response to improve salt tolerance in soybean.

Identification of the CIPK-CBL family gene and functional characterization of CqCIPK14 gene under drought stress in quinoa

Background

Calcineurin-like Protein (CBL) and CBL interacting protein kinase (CIPK) play a key role in plant signal transduction and response to various environmental stimuli. Quinoa, as an important plant with high nutritional value, can meet the basic nutritional needs of human Cash crop, is also susceptible to abiotic stress. However, CBL-CIPK in quinoa have not been reported.

Results

In this study, 16 CBL and 41 CIPK genes were identified in quinoa. CBL-CIPK gene shows different intron-exon gene structure and motif, they participate in different biological processes, and form a complex regulatory network between CBL-CIPK proteins. Many cis-regulatory element associated with ABA and drought have been found. The expression patterns of CBL-CIPK showed different expression patterns in various abiotic stresses and tissues. RT-qPCR showed that most members of these two gene families were involved in drought regulation of quinoa, in particular, the expression levels of CqCIPK11, CqCIPK15, CqCIPK37 and CqCBL13 increased significantly under drought stress.

Conclusions

The structures and functions of the CBL-CIPK family in quinoa were systematically explored. Many CBL-CIPK may play vital roles in the regulation of organ development, growth, and responses to abiotic stresses. This research has great significance for the functional characterisation of the quinoa CBL-CIPK family and our understanding of the CBL-CIPK family in higher plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08683-6.

Mecanismos de defensa en plantas de Capsicum contra Phytophthora capsici

Phytophthora capsici es un oomiceto causante de la pudrición de raíz, tallo, frutos y tizón foliar en varias especies vegetales de importancia agrícola, principalmente en Solanáceas del género Capsicum como ají y pimiento. Este fitopatógeno cosmopolita posee mecanismos de ataque que favorecen la rápida infección, colonización y reproducción en huéspedes susceptibles. Contrariamente, estos procesos son retrasados o evitados fuertemente por genotipos resistentes, debido principalmente a sus mecanismos de defensa. En esas interacciones incompatibles, las plantas resistentes de Capsicum reconocen el oomiceto y rápidamente expresan múltiples genes que posteriormente señalizan moléculas, que permiten la acumulación de compuestos fenólicos, fitoalexinas y especies reactivas de oxígeno, la actividad de diferentes enzimas, que pueden permitir incluso la formación de barreras físicas. Esta revisión aborda, expone y discute los avances y el progreso de las investigaciones a lo largo de los ultimos veinte años, referente a los mecanismos de defensa estructurales, bioquimicos y moleculares que utilizan las plantas resistentes de Capsicum para defenderse de P. capsici. Palabras claves. ají, pimiento, pudrición de raíz y corona, tizón foliar, resistencia vegetal

Insight into the CBL and CIPK gene families in pecan (Carya illinoinensis): identification, evolution and expression patterns in drought response

BACKGROUND

Calcium (Ca²⁺) serves as a ubiquitous second messenger and plays a pivotal role in signal transduction. Calcineurin B-like proteins (CBLs) are plant-specific Ca²⁺ sensors that interact with CBL-interacting protein kinases (CIPKs) to transmit Ca²⁺ signals. CBL-CIPK complexes have been reported to play pivotal roles in plant development and response to drought stress; however, limited information is available about the CBL and CIPK genes in pecan, an important nut crop.

RESULTS

In the present study, a total of 9 CBL and 30 CIPK genes were identified from the pecan genome and divided into four and five clades based on phylogeny, respectively. Gene structure and distribution of conserved sequence motif analysis suggested that family members in the same clade commonly exhibited similar exon-intron structures and motif compositions. The segmental duplication events contributed largely to the expansion of pecan CBL and CIPK gene families, and Ka/Ks values revealed that all of them experienced strong negative selection. Phylogenetic analysis of CIPK proteins from 14 plant species revealed that CIPKs in the intron-poor clade originated in seed plants. Tissue-specific expression profiles of CiCBLs and CiCIPKs were analysed, presenting functional diversity. Expression profiles derived from RNA-Seq revealed distinct expression patterns of CiCBLs and CiCIPKs under drought treatment in pecan. Moreover, coexpression network analysis helped to elucidate the relationships between these genes and identify potential candidates for the regulation of drought response, which were verified by qRT-PCR analysis.

CONCLUSIONS

The characterization and analysis of CBL and CIPK genes in pecan genome could provide a basis for further functional analysis of CiCBLs and CiCIPKs in the drought stress response of pecan.

Calcium Mediated Cold Acclimation in Plants: Underlying Signaling and Molecular Mechanisms

Exposure of plants to low temperatures adversely affects plant growth, development, and productivity. Plant response to cold stress is an intricate process that involves the orchestration of various physiological, signaling, biochemical, and molecular pathways. Calcium (Ca²⁺) signaling plays a crucial role in the acquisition of several stress responses, including cold. Upon perception of cold stress, Ca²⁺ channels and/or Ca²⁺ pumps are activated, which induces the Ca²⁺ signatures in plant cells. The Ca²⁺ signatures spatially and temporally act inside a plant cell and are eventually decoded by specific Ca²⁺ sensors. This series of events results in the molecular regulation of several transcription factors (TFs), leading to downstream gene expression and withdrawal of an appropriate response by the plant. In this context, calmodulin binding transcription activators (CAMTAs) constitute a group of TFs that regulate plant cold stress responses in a Ca²⁺ dependent manner. The present review provides a catalog of the recent progress made in comprehending the Ca²⁺ mediated cold acclimation in plants.

The CBL-interacting protein kinase CaCIPK13 positively regulates defence mechanisms against cold stress in pepper

Cold stress is one of the main factors limiting growth and development in pepper. Calcineurin B-like proteins (CBLs) are specific calcium sensors with non-canonical EF-hands to capture calcium signals, and interact with CBL-interacting protein kinases (CIPKs) in the regulation of various stresses. In this study, we isolated a cold-induced CIPK gene from pepper named CaCIPK13, which encodes a protein of 487 amino acids. In silico analyses indicated that CaCIPK13 is a typical CIPK family member with a conserved NAF motif, which consists of the amino acids asparagine, alanine, and phenylalanine. The CaCIPK13 protein was located in the nucleus and plasma membrane. Knock down of CaCIPK13 resulted in enhanced sensitivity to cold stress in pepper, with increased malondialdehyde content, H2O2 accumulation, and electrolyte leakage, while the catalase, peroxidase, superoxide dismutase activities and anthocyanin content were decreased. The transcript level of cold and anthocyanin-related genes was substantially decreased in CaCIPK13-silenced pepper leaves relative to the empty vector control. On the contrary, overexpression of CaCIPK13 in tomato improved cold tolerance via increasing anthocyanin content and activities of reactive oxygen species scavenging enzymes. Furthermore, the interaction of CaCIPK13 with CaCBL1/6/7/8 was Ca2+-dependent. These results indicate that CaCIPK13 plays a positive role in cold tolerance mechanism via CBL-CIPK signalling.

Genome-wide identification and expression analysis of HAK/KUP/KT potassium transporter provides insights into genes involved in responding to potassium deficiency and salt stress in pepper (Capsicum annuum L.)

In plants, the HAK/KUP/KT family is the largest group of potassium transporters, and it plays an important role in mineral element absorption, plant growth, environmental stress adaptation, and symbiosis. Although these important genes have been investigated in many plant species, limited information is currently available on the HAK/KUP/KT genes for Pepper (Capsicum annuum L.). In the present study, a total of 20 CaHAK genes were identified from the pepper genome and the CaHAK genes were numbered 1 - 20 based on phylogenetic analysis. For the genes and their corresponding proteins, the physicochemical properties, phylogenetic relationship, chromosomal distribution, gene structure, conserved motifs, gene duplication events, and expression patterns were analyzed. Phylogenetic analysis divided CaHAK genes into four cluster (I-IV) based on their structural features and the topology of the phylogenetic tree. Purifying selection played a crucial role in the evolution of CaHAK genes, while whole-genome triplication contributed to the expansion of the CaHAK gene family. The expression patterns showed that CaHAK proteins exhibited functional divergence in terms of plant K⁺ uptake and salt stress response. In particular, transcript abundance of CaHAK3 and CaHAK7 was strongly and specifically up-regulated in pepper roots under low K⁺ or high salinity conditions, suggesting that these genes are candidates for high-affinity K⁺ uptake transporters and may play crucial roles in the maintenance of the Na⁺/K⁺ balance during salt stress in pepper. In summary, the results not only provided the important information on the characteristics and evolutionary relationships of CaHAKs, but also provided potential genes responding to potassium deficiency and salt stress.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03136-z.

New functions of CIPK gene family are continue to emerging

CIPK protein family is a key protein family in Ca²⁺ mediated plant signaling pathway, which plays an indispensable role in plant response to stress and development. Every gene in this family encodes specific proteins. They interact with calcium ion signals, make plants to deal with various stress or stimuli. This article mainly reviews the mechanism, positioning and physiological functions of the CIPK family in different species in recent years. According to our team's research, CIPK8 interacts with CBL5 to improve salt tolerance, and CIPK23 interacts with TGA1 to regulate nitrate uptake negatively in chrysanthemum. In addition, we discussed current limitations and future research directions. The article will enhance the understanding of the functional characteristics of the CIPK gene family under different stresses, provide insights for future breeding and the development of new crop varieties with enhanced stress tolerance.

Deciphering the Host-Pathogen Interactome of the Wheat-Common Bunt System: A Step towards Enhanced Resilience in Next Generation Wheat

Common bunt, caused by two fungal species, Tilletia caries and Tilletia laevis, is one of the most potentially destructive diseases of wheat. Despite the availability of synthetic chemicals against the disease, organic agriculture relies greatly on resistant cultivars. Using two computational approaches—interolog and domain-based methods—a total of approximately 58 M and 56 M probable PPIs were predicted in T. aestivum–T. caries and T. aestivum–T. laevis interactomes, respectively. We also identified 648 and 575 effectors in the interactions from T. caries and T. laevis, respectively. The major host hubs belonged to the serine/threonine protein kinase, hsp70, and mitogen-activated protein kinase families, which are actively involved in plant immune signaling during stress conditions. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the host proteins revealed significant GO terms (O-methyltransferase activity, regulation of response to stimulus, and plastid envelope) and pathways (NF-kappa B signaling and the MAPK signaling pathway) related to plant defense against pathogens. Subcellular localization suggested that most of the pathogen proteins target the host in the plastid. Furthermore, a comparison between unique T. caries and T. laevis proteins was carried out. We also identified novel host candidates that are resistant to disease. Additionally, the host proteins that serve as transcription factors were also predicted.

Identification of Fruit Traits Related QTLs and a Candidate Gene, CaBRX, Controlling Locule Number in Pepper (Capsicum annuum L.)

Fruit traits are important in pepper (Capsicum annuum L.) and affect its quality and yield. These traits are controlled by quantitative trait loci (QTLs). In this study, we identified many major QTLs that control fruit length (Ftl), fruit diameter (Ftd), fruit shape (Fts), fruit weight (Ftw) and locule number (Lcn) in the F2 and F2:3 populations developed from the QTL mapping of GS6 (P1) and Qiemen (P2). A total of 111 simple sequence repeats and insertion/deletion markers were utilized to construct a linkage map with 12 linkage groups over a length of 1320.72 cM. An inclusive composite interval mapping analysis indicated that many QTLs were detected and included ftl2.1, ftd2.1, fts1.1, ftw2.1 and lcn1.1. As a novel QTL, lcn1.1 was located between HM1112 and EPMS709, and the genetic distance was 3.18 cM covering 60 predicted genes. Within the region, we identified Capana01g004285 as a candidate gene by functional annotation and expression analysis and found that it encodes the BREVIS RADIX (BRX) protein. Knockdown of CaBRX through the virus-induced gene silencing approach in GS6 reduced the number of locules and influenced the expressions of genes related to flower and locule development, suggesting that CaBRX plays an important function in the development of locules.

Genome-Wide Identification, Characterization and Expression Analysis of the CIPK Gene Family in Potato (Solanum tuberosum L.) and the Role of StCIPK10 in Response to Drought and Osmotic Stress

The potato (Solanum tuberosum L.), one of the most important food crops worldwide, is sensitive to environmental stresses. Sensor–responder complexes comprising calcineurin B-like (CBL) proteins and CBL-interacting protein kinases (CIPKs) not only modulate plant growth and development but also mediate numerous stress responses. Here, using a Hidden Markov Model and BLAST searches, 27 CIPK genes were identified in potato and divided into five groups by phylogenetic analysis and into two clades (intron-poor and intron-rich) by gene structure analysis. Quantitative reverse-transcription PCR (qRT-PCR) assays revealed that StCIPK genes play important roles in plant growth, development and abiotic stress tolerance. Up-regulated expression of StCIPK10 was significantly induced by drought, PEG6000 and ABA. StCIPK10 enhances both the ability of potato to scavenge reactive oxygen species and the content of corresponding osmoregulation substances, thereby strengthening tolerance to drought and osmotic stress. StCIPK10 is located at the intersection between the abscisic acid and abiotic stress signaling pathways, which control both root growth and stomatal closure in potato. In addition, StCIPK10 interacts with StCBL1, StCBL4, StCBL6, StCBL7, StCBL8, StCBL11 and StCBL12, and is specifically recruited to the plasma membrane by StCBL11.

Genome-Wide Identification of CBL-CIPK Gene Family in Honeysuckle (Lonicera japonica Thunb.) and Their Regulated Expression Under Salt Stress

In plants, calcineurin B-like proteins (CBLs) are a unique group of Ca²⁺ sensors that decode Ca²⁺ signals by activating a family of plant-specific protein kinases known as CBL-interacting protein kinases (CIPKs). CBL-CIPK gene families and their interacting complexes are involved in regulating plant responses to various environmental stimuli. To gain insight into the functional divergence of CBL-CIPK genes in honeysuckle, a total of six LjCBL and 17 LjCIPK genes were identified. The phylogenetic analysis along with the gene structure analysis divided both CBL and CBL-interacting protein kinase genes into four subgroups and validated by the distribution of conserved protein motifs. The 3-D structure prediction of proteins shown that most LjCBLs shared the same Protein Data Bank hit 1uhnA and most LjCIPKs shared the 6c9Da. Analysis of cis-acting elements and gene ontology implied that both LjCBL and LjCIPK genes could be involved in hormone signal responsiveness and stress adaptation. Protein-protein interaction prediction suggested that LjCBL4 is hypothesized to interact with LjCIPK7/9/15/16 and SOS1/NHX1. Gene expression analysis in response to salinity stress revealed that LjCBL2/4, LjCIPK1/15/17 under all treatments gradually increased over time until peak expression at 72 h. These results demonstrated the conservation of salt overly sensitive pathway genes in honeysuckle and a model of Ca²⁺-LjCBL4/LjSOS3-LjCIPK16/LjSOS2 module-mediated salt stress signaling in honeysuckle is proposed. This study provides insight into the characteristics of the CBL-CIPK gene families involved in honeysuckle salt stress responses, which could serve as a foundation for gene transformation technology, to obtain highly salt-tolerant medicinal plants in the context of the global reduction of cultivated land.

Genome-Wide Analysis of the Apple CBL Family Reveals That Mdcbl10.1 Functions Positively in Modulating Apple Salt Tolerance

Abiotic stresses are increasingly harmful to crop yield and quality. Calcium and its signaling pathway play an important role in modulating plant stress tolerance. As specific Ca²⁺ sensors, calcineurin B-like (CBL) proteins play vital roles in plant stress response and calcium signaling. The CBL family has been identified in many plant species; however, the characterization of the CBL family and the functional study of apple MdCBL proteins in salt response have yet to be conducted in apple. In this study, 11 MdCBL genes were identified from the apple genome. The coding sequences of these MdCBL genes were cloned, and the gene structure and conserved motifs were analyzed in detail. The phylogenetic analysis indicated that these MdCBL proteins could be divided into four groups. The functional identification in Na⁺-sensitive yeast mutant showed that the overexpression of seven MdCBL genes could confer enhanced salt stress resistance in transgenic yeast. The function of MdCBL10.1 in regulating salt tolerance was also verified in cisgenic apple calli and apple plants. These results provided valuable insights for future research examining the function and mechanism of CBL proteins in regulating apple salt tolerance.

The CaCIPK3 gene positively regulates drought tolerance in pepper

Drought stress is a major agricultural problem restricting the growth, development, and productivity of plants. Calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs) significantly influence the plant response to different stresses. However, the molecular mechanisms of CBL-CIPK in the drought stress response of pepper are still unknown. Here, the function of CaCIPK3 in the regulation of drought stress in pepper (Capsicum annuum L.) was explored. Transcriptomic data and quantitative real-time PCR (qRT-PCR) analysis revealed that CaCIPK3 participates in the response to multiple stresses. Knockdown of CaCIPK3 in pepper increased the sensitivity to mannitol and methyl jasmonate (MeJA). Transient overexpression of CaCIPK3 improved drought tolerance by enhancing the activities of the antioxidant system and positively regulating jasmonate (JA)-related genes. Ectopic expression of CaCIPK3 in tomato also improved drought and MeJA resistance. As the CaCIPK3-interacting partner, CaCBL2 positively influenced drought resistance. Additionally, CaWRKY1 and CaWRKY41 directly bound the CaCIPK3 promoter to influence its expression. This study shows that CaCIPK3 acts as a positive regulator in drought stress resistance via the CBL-CIPK network to regulate MeJA signaling and the antioxidant defense system.

Overexpression of NtCBL5A Leads to Necrotic Lesions by Enhancing Na+ Sensitivity of Tobacco Leaves Under Salt Stress

Many tobacco (Nicotiana tabacum) cultivars are salt-tolerant and thus are potential model plants to study the mechanisms of salt stress tolerance. The CALCINEURIN B-LIKE PROTEIN (CBL) is a vital family of plant calcium sensor proteins that can transmit Ca²⁺ signals triggered by environmental stimuli including salt stress. Therefore, assessing the potential of NtCBL for genetic improvement of salt stress is valuable. In our studies on NtCBL members, constitutive overexpression of NtCBL5A was found to cause salt supersensitivity with necrotic lesions on leaves. NtCBL5A-overexpressing (OE) leaves tended to curl and accumulated high levels of reactive oxygen species (ROS) under salt stress. The supersensitivity of NtCBL5A-OE leaves was specifically induced by Na⁺, but not by Cl^-, osmotic stress, or drought stress. Ion content measurements indicated that NtCBL5A-OE leaves showed sensitivity to the Na⁺ accumulation levels that wild-type leaves could tolerate. Furthermore, transcriptome profiling showed that many immune response-related genes are significantly upregulated and photosynthetic machinery-related genes are significantly downregulated in salt-stressed NtCBL5A-OE leaves. In addition, the expression of several cation homeostasis-related genes was also affected in salt-stressed NtCBL5A-OE leaves. In conclusion, the constitutive overexpression of NtCBL5A interferes with the normal salt stress response of tobacco plants and leads to Na⁺-dependent leaf necrosis by enhancing the sensitivity of transgenic leaves to Na⁺. This Na⁺ sensitivity of NtCBL5A-OE leaves might result from the abnormal Na⁺ compartmentalization, plant photosynthesis, and plant immune response triggered by the constitutive overexpression of NtCBL5A. Identifying genes and pathways involved in this unusual salt stress response can provide new insights into the salt stress response of tobacco plants.

Regulation of drought-related responses in tomato plants by two classes of calcineurin B-like (SlCBL1/2) proteins

Calcineurin-B-like proteins (CBLs) are essential components of the calcium signaling network and act during plant's response to stress and normal conditions. A combined research strategy of in-silico analysis and gene silencing experiment was employed to investigate the role of different classes of CBLs in tomato (Solanum lycopersicum L.) during the response to drought stress. Two different classes of CBL genes, including SlCBL3-1, and SlCBL3-2, with the minimum and a maximum number of drought-responsive cis-elements, were selected and were targeted for transient gene silencing in tomato followed by the drought treatment. The effect of silencing events was evaluated by determining of further growth and physiological traits in plants under both control and drought stress conditions. The results showed that silencing of SlCBL3-1 significantly reduced shoot and root growth, relative water content (RWC), and the concentration of pigments while increased free radical accumulation, lipid peroxidation, and leakage from the cells. On the other hand, no antioxidant enzyme activity or proline induction was triggered in plants after SlCBL3-1 silencing. Some of these adverse events were more significantly enhanced when the silenced plants were exposed to drought stress. Overall, a significant role for SlCBL3-1 in the life cycle of plant suggested under both normal and stress conditions. The SlCBL3-2 silencing showed more efficient plants recovery from silencing or drought stress conditions. Therefore, SlCBL3-2 gene may act as a negative regulator under stress conditions. The results might provide new theoretical insight and genetic resources for developing resistant crops against environmental stresses.

Isolation and characterization of Salt Overly Sensitive family genes in spinach

The Salt Overly Sensitive (SOS) pathway regulates intracellular sodium ion homeostasis as a salt-stress response in plants. This pathway involves three main genes designated as SOS1, SOS2 and SOS3, which are members of the Na⁺ /H⁺ exchanger (NHX), CBL-interacting protein kinase (CIPK) and Calcineurin B-like (CBL) gene families, respectively. To identify and characterize SOS genes in spinach (Spinacia oleracea), a species of the Amaranthaceae family, we conducted genome-wide identification and phylogenetic analyses of NHX, CIPK and CBL genes from four Amaranthaceae species, Arabidopsis and rice. Most Amaranthaceae genes exhibited orthologous relationships with Arabidopsis and/or rice, except a clade of Vac-type Amaranthaceae NHX genes. Phylogenetic analyses also revealed gene gain/loss events in Amaranthaceae species and the intron-less to intron-rich evolution of CIPK genes. A bacterial protein-rooted CIPK tree allowed naming most of the phylogenetic clades based on their evolutionary history. Single S. oleracea (So) SOS1, SOS2 and SOS3 proteins were identified. Direct protein-protein interaction was observed between SoSOS2 and SoSOS3 but not between SoSOS2 and SoSOS1 based on yeast two-hybrid assay. This may suggest distinct modes of action of spinach SOS proteins compared to Arabidopsis SOS proteins. Unlike SoSOS1 and SoSOS2, which were expressed at similar or higher levels in leaves than roots, SoSOS3 expression was significantly higher in roots than leaves, suggesting its greater importance in roots. The expression of SoSOS3 was upregulated in both roots and leaves under salinity compared to the control; however, SoSOS1 was only upregulated in roots. Thus, this study demonstrated the conservation of SOS pathway genes in spinach and also highlighted the complexity of SOS signaling in Amaranthaceae species.

Genome-Wide Identification and Capsaicinoid Biosynthesis-Related Expression Analysis of the R2R3-MYB Gene Family in Capsicum annuum L

Capsaicinoids are naturally specialized metabolites in pepper and are the main reason that Capsicum fruits have a pungent smell. During the synthesis of capsaicin, MYB transcription factors play key regulatory roles. In particular, R2R3-MYB subfamily genes are the most important members of the MYB family and are critical candidate factors in capsaicinoid biosynthesis. The 108 R2R3-MYB genes in pepper were identified in this study and all are shown to have two highly conserved MYB binding domains. Phylogenetic and structural analyses clustered CaR2R3-MYB genes into seven groups. Interspecies collinearity analysis found that the R2R3-MYB family contains 16 duplicated gene pairs and the highest gene density is on chromosome 00 and 03. The expression levels of CaR2R3-MYB differentially expressed genes (DEGs) and capsaicinoid-biosynthetic genes (CBGs) in fruit development stages were obtained via RNA-seq and quantitative polymerase chain reaction (qRT-PCR). Co-expression analyses reveal that highly expressed CaR2R3-MYB genes are co-expressed with CBGs during early stages of pericarp and placenta development processes. It is speculated that six candidate CaR2R3-MYB genes are involved in regulating the synthesis of capsaicin and dihydrocapsaicin. This study is the first systematic analysis of the CaR2R3-MYB gene family and provided references for studying their molecular functions. At the same time, these results also laid the foundation for further research on the capsaicin characteristics of CaR2R3-MYB genes in pepper.

The CBL-CIPK Pathway in Plant Response to Stress Signals

Plants need to cope with multitudes of stimuli throughout their lifecycles in their complex environments. Calcium acts as a ubiquitous secondary messenger in response to numerous stresses and developmental processes in plants. The major Ca2+ sensors, calcineurin B-like proteins (CBLs), interact with CBL-interacting protein kinases (CIPKs) to form a CBL-CIPK signaling network, which functions as a key component in the regulation of multiple stimuli or signals in plants. In this review, we describe the conserved structure of CBLs and CIPKs, characterize the features of classification and localization, draw conclusions about the currently known mechanisms, with a focus on novel findings in response to multiple stresses, and summarize the physiological functions of the CBL-CIPK network. Moreover, based on the gradually clarified mechanisms of the CBL-CIPK complex, we discuss the present limitations and potential prospects for future research. These aspects may provide a deeper understanding and functional characterization of the CBL-CIPK pathway and other signaling pathways under different stresses, which could promote crop yield improvement via biotechnological intervention.

The CaChiVI2 Gene of Capsicum annuum L. Confers Resistance Against Heat Stress and Infection of Phytophthora capsici

Extreme environmental conditions seriously affect crop growth and development, resulting in substantial reduction in yield and quality. However, chitin-binding proteins (CBP) family member CaChiVI2 plays a crucial role in eliminating the impact of adverse environmental conditions, such as cold and salt stress. Here, for the first time it was discovered that CaChiVI2 (Capana08g001237) gene of pepper (Capsicum annuum L.) had a role in resistance to heat stress and physiological processes. The full-length open-reading frame (ORF) of CaChiVI2 (606-bp, encoding 201-amino acids), was cloned into TRV2:CaChiVI2 vector for silencing. The CaChiVI2 gene carries heat shock elements (HSE, AAAAAATTTC) in the upstream region, and thereby shows sensitivity to heat stress at the transcriptional level. The silencing effect of CaChiVI2 in pepper resulted in increased susceptibility to heat and Phytophthora capsici infection. This was evident from the severe symptoms on leaves, the increase in superoxide (O2 -) and hydrogen peroxide (H2O2) accumulation, higher malondialdehyde (MDA), relative electrolyte leakage (REL) and lower proline contents compared with control plants. Furthermore, the transcript level of other resistance responsive genes was also altered. In addition, the CaChiIV2-overexpression in Arabidopsis thaliana showed mild heat and drought stress symptoms and increased transcript level of a defense-related gene (AtHSA32), indicating its role in the co-regulation network of the plant. The CaChiVI2-overexpressed plants also showed a decrease in MDA contents and an increase in antioxidant enzyme activity and proline accumulation. In conclusion, the results suggest that CaChiVI2 gene plays a decisive role in heat and drought stress tolerance, as well as, provides resistance against P. capsici by reducing the accumulation of reactive oxygen species (ROS) and modulating the expression of defense-related genes. The outcomes obtained here suggest that further studies should be conducted on plants adaptation mechanisms in variable environments.

Chloroplast Calcium Signaling in the Spotlight

Calcium has long been known to regulate the metabolism of chloroplasts, concerning both light and carbon reactions of photosynthesis, as well as additional non photosynthesis-related processes. In addition to undergo Ca²⁺ regulation, chloroplasts can also influence the overall Ca²⁺ signaling pathways of the plant cell. Compelling evidence indicate that chloroplasts can generate specific stromal Ca²⁺ signals and contribute to the fine tuning of cytoplasmic Ca²⁺ signaling in response to different environmental stimuli. The recent set up of a toolkit of genetically encoded Ca²⁺ indicators, targeted to different chloroplast subcompartments (envelope, stroma, thylakoids) has helped to unravel the participation of chloroplasts in intracellular Ca²⁺ handling in resting conditions and during signal transduction. Intra-chloroplast Ca²⁺ signals have been demonstrated to occur in response to specific environmental stimuli, suggesting a role for these plant-unique organelles in transducing Ca²⁺-mediated stress signals. In this mini-review we present current knowledge of stimulus-specific intra-chloroplast Ca²⁺ transients, as well as recent advances in the identification and characterization of Ca²⁺-permeable channels/transporters localized at chloroplast membranes. In particular, the potential role played by cMCU, a chloroplast-localized member of the mitochondrial calcium uniporter (MCU) family, as component of plant environmental sensing is discussed in detail, taking into account some specific structural features of cMCU. In summary, the recent molecular identification of some players of chloroplast Ca²⁺ signaling has opened new avenues in this rapidly developing field and will hopefully allow a deeper understanding of the role of chloroplasts in shaping physiological responses in plants.