The ankyrin repeat gene family in rice: genome-wide identification, classification and expression profiling

Genome-wide identification of Ankyrin (ANK) repeat gene families in three Dendrobium species and the expression of ANK genes in D. officinale under gibberellin and abscisic acid treatments

BACKGROUND

Dendrobium Sw. represents one of the most expansive genera within the Orchidaceae family, renowned for its species' high medicinal and ornamental value. In higher plants, the ankyrin (ANK) repeat protein family is characterized by a unique ANK repeat domain, integral to a plethora of biological functions and biochemical activities. The ANK gene family plays a pivotal role in various plant physiological processes, including stress responses, hormone signaling, and growth. Hence, investigating the ANK gene family and identifying disease-resistance genes in Dendrobium is of paramount importance.

RESULTS

This research identified 78 ANK genes in Dendrobium officinale Kimura et Migo, 77 in Dendrobium nobile Lindl., and 58 in Dendrobium chrysotoxum Lindl. Subsequently, we conducted comprehensive bioinformatics analyses on these ANK gene families, encompassing gene classification, chromosomal localization, phylogenetic relationships, gene structure and motif characterization, cis-acting regulatory element identification, collinearity assessment, protein-protein interaction network construction, and gene expression profiling. Concurrently, three DoANK genes (DoANK14, DoANK19, and DoANK47) in D. officinale were discerned to indirectly activate the NPR1 transcription factor in the ETI system via SA, thereby modulating the expression of the antibacterial PR gene. Hormonal treatments with GA3 and ABA revealed that 17 and 8 genes were significantly up-regulated, while 4 and 8 genes were significantly down-regulated, respectively. DoANK32 was found to localize to the ArfGAP gene in the endocytosis pathway, impacting vesicle transport and the polar movement of auxin.

CONCLUSION

Our findings provide a robust framework for the taxonomic classification, evolutionary analysis, and functional prediction of Dendrobium ANK genes. The three highlighted ANK genes (DoANK14, DoANK19, and DoANK47) from D. officinale may prove valuable in disease resistance and stress response research. DoANK32 is implicated in the morphogenesis and development of D. officinale through its role in vesicular transport and auxin polarity, with subcellular localization studies confirming its presence in the nucleus and cell membrane. ANK genes displaying significant expression changes in response to hormonal treatments could play a crucial role in the hormonal response of D. officinale, potentially inhibiting its growth and development through the modulation of plant hormones such as GA3 and ABA.

Tiller Number1 encodes an ankyrin repeat protein that controls tillering in bread wheat

Wheat (Triticum aestivum L.) is a major staple food for more than one-third of the world's population. Tiller number is an important agronomic trait in wheat, but only few related genes have been cloned. Here, we isolate a wheat mutant, tiller number1 (tn1), with much fewer tillers. We clone the TN1 gene via map-based cloning: TN1 encodes an ankyrin repeat protein with a transmembrane domain (ANK-TM). We show that a single amino acid substitution in the third conserved ankyrin repeat domain causes the decreased tiller number of tn1 mutant plants. Resequencing and haplotype analysis indicate that TN1 is conserved in wheat landraces and modern cultivars. Further, we reveal that the expression level of the abscisic acid (ABA) biosynthetic gene TaNCED3 and ABA content are significantly increased in the shoot base and tiller bud of the tn1 mutants; TN1 but not tn1 could inhibit the binding of TaPYL to TaPP2C via direct interaction with TaPYL. Taken together, we clone a key wheat tiller number regulatory gene TN1, which promotes tiller bud outgrowth probably through inhibiting ABA biosynthesis and signaling.

Bioinformatics Analysis of WRKY Family Genes in Erianthus fulvus Ness

One of the most prominent transcription factors in higher plants, the WRKY gene family, is crucial for secondary metabolism, phytohormone signaling, plant defense responses, and plant responses to abiotic stresses. It can control the expression of a wide range of target genes by coordinating with other DNA-binding or non-DNA-binding interacting proteins. In this study, we performed a genome-wide analysis of the EfWRKY genes and initially identified 89 members of the EfWRKY transcription factor family. Using some members of the OsWRKY transcription factor family, an evolutionary tree was built using the neighbor-joining (NJ) method to classify the 89 members of the EfWRKY transcription factor family into three major taxa and one unclassified group. Molecular weights ranged from 22,614.82 to 303,622.06 Da; hydrophilicity ranged from (−0.983)–(0.159); instability coefficients ranged from 40.97–81.30; lipid coefficients ranged from 38.54–91.89; amino acid numbers ranged from 213–2738 bp; isoelectric points ranged from 4.85–10.06. A signal peptide was present in EfWRKY41 but not in the other proteins, and EfWRK85 was subcellularly localized to the cell membrane. Chromosome localization revealed that the WRKY gene was present on each chromosome, proving that the conserved pattern WRKYGQK is the family’s central conserved motif. Conserved motif analysis showed that practically all members have this motif. Analysis of the cis-acting elements indicated that, in addition to the fundamental TATA-box, CAAT-box, and light-responsive features (GT1-box), there are response elements implicated in numerous hormones, growth regulation, secondary metabolism, and abiotic stressors. These results inform further studies on the function of EfWRKY genes and will lead to the improvement of sugarcane.

Genomic and transcriptomic analyses provide insights into valuable fatty acid biosynthesis and environmental adaptation of yellowhorn

Yellowhorn (Xanthoceras sorbifolium) is an oil-bearing tree species growing naturally in poor soil. The kernel of yellowhorn contains valuable fatty acids like nervonic acid. However, the genetic basis underlying the biosynthesis of valued fatty acids and adaptation to harsh environments is mainly unexplored in yellowhorn. Here, we presented a haplotype-resolved chromosome-scale genome assembly of yellowhorn with the size of 490.44 Mb containing scaffold N50 of 34.27 Mb. Comparative genomics, in combination with transcriptome profiling analyses, showed that expansion of gene families like long-chain acyl-CoA synthetase and ankyrins contribute to yellowhorn fatty acid biosynthesis and defense against abiotic stresses, respectively. By integrating genomic and transcriptomic data of yellowhorn, we found that the transcription of 3-ketoacyl-CoA synthase gene XS04G00959 was consistent with the accumulation of nervonic and erucic acid biosynthesis, suggesting its critical regulatory roles in their biosynthesis. Collectively, these results enhance our understanding of the genetic basis underlying the biosynthesis of valuable fatty acids and adaptation to harsh environments in yellowhorn and provide foundations for its genetic improvement.

Genome-Wide Association Mapping Reveals Novel Putative Gene Candidates Governing Reproductive Stage Heat Stress Tolerance in Rice

Temperature rise predicted for the future will severely affect rice productivity because the crop is highly sensitive to heat stress at the reproductive stage. Breeding tolerant varieties is an economically viable option to combat heat stress, for which the knowledge of target genomic regions associated with the reproductive stage heat stress tolerance (RSHT) is essential. A set of 192 rice genotypes of diverse origins were evaluated under natural field conditions through staggered sowings for RSHT using two surrogate traits, spikelet fertility and grain yield, which showed significant reduction under heat stress. These genotypes were genotyped using a 50 k SNP array, and the association analysis identified 10 quantitative trait nucleotides (QTNs) for grain yield, of which one QTN (qHTGY8.1) was consistent across the different models used. Only two out of 10 MTAs coincided with the previously reported QTLs, making the remaing eight novel. A total of 22 QTNs were observed for spikelet fertility, among which qHTSF5.1 was consistently found across three models. Of the QTNs identified, seven coincided with previous reports, while the remaining QTNs were new. The genes near the QTNs were found associated with the protein–protein interaction, protein ubiquitination, stress signal transduction, and so forth, qualifying them to be putative for RSHT. An in silico expression analysis revealed the predominant expression of genes identified for spikelet fertility in reproductive organs. Further validation of the biological relevance of QTNs in conferring heat stress tolerance will enable their utilization in improving the reproductive stage heat stress tolerance in rice.

Genetic Mapping to Detect Stringent QTLs Using 1k-RiCA SNP Genotyping Platform from the New Landrace Associated with Salt Tolerance at the Seedling Stage in Rice

Rice is the world’s most important food crop, providing the daily calorie intake for more than half of the world’s population. Rice breeding has always been preoccupied with maximizing yield potential. However, numerous abiotic factors, such as salt, cold, drought, and heat, significantly reduce rice productivity. Salinity, one of the major abiotic stresses, reduces rice yield worldwide. This study was conducted to determine new quantitative trait loci (QTLs) that regulate salt tolerance in rice seedlings. One F_2:3 mapping population was derived from a cross between BRRI dhan49 (a popular but sensitive rainfed rice variety) and Akundi (a salt-tolerant rice landrace in Bangladesh used as a donor parent). The 1k-Rice Custom Amplicon (1k-RiCA) single-nucleotide polymorphism (SNP) markers were used to genotype this mapping population. After removing segregation distortion and monomorphic markers, 884 SNPs generated a 1526.8 cM-long genetic linkage map with a mean marker density of 1.7 cM for the 12 linkage groups. By exploiting QGene and ICIM-ADD, a sum of 15 QTLs for nine traits was identified in salt stress on seven chromosomes. Four important genomic loci were identified (qSES1, qSL1, qSUR1 and qRL1) on chromosome 1. Out of these 15 QTLs, 14 QTLs are unique, as no other study has mapped in the same chromosomal location. We also detected 15 putative candidate genes and their functions. The ICIM-EPI approach identified 43 significant pairwise epistasis interactions between regions associated with and unassociated with QTLs. Apart from more well-known donors, Akundi serves as an important new donor source for global salt tolerance breeding initiatives, including Bangladesh. The introgression of the novel QTLs identified in this study will accelerate the development of new salt-tolerant varieties that are highly resistant to salt stress using marker-enabled breeding.

Capturing acyltransferase(s) transforming final step in the biosynthesis of a major Iridoid Glycoside, (Picroside-II) in a Himalayan Medicinal Herb, Picrorhiza kurroa

BACKGROUND

Picrorhiza kurroa has been reported as an age-old ayurvedic hepato-protection to treat hepatic disorders due to the presence of iridoids such as picroside-II (P-II), picroside-I, and kutkoside. The acylation of catalpol and vanilloyl coenzyme A by acyltransferases (ATs) is critical step in P-II biosynthesis. Since accumulation of P-II occurs only in roots, rhizomes and stolons in comparison to leaves uprooting of this critically endangered herb has been the only source of this compound. Recently, we reported that P-II acylation likely happen in roots, while stolons serve as the vital P-II storage compartment. Therefore, developing an alternate engineered platform for P-II biosynthesis require identification of P-II specific AT/s.

METHODS AND RESULTS

In that direction, egg-NOG function annotated 815 ATs from de novo RNA sequencing of tissue culture based 'shoots-only' system and nursery grown shoots, roots, and stolons varying in P-II content, were cross-compared in silico to arrive at ATs sequences unique and/or common to stolons and roots. Verification for organ and accession-wise upregulation in gene expression of these ATs by qRT-PCR has shortlisted six putative 'P-II-forming' ATs. Further, six-frame translation, ab initio protein structure modelling and protein-ligand molecular docking of these ATs signified one MBOAT domain containing AT with preferential binding to the vanillic acid CoA thiol ester as well as with P-II, implying that this could be potential AT decorating final structure of P-II.

CONCLUSIONS

Organ-wise comparative transcriptome mining coupled with reverse transcription real time qRT-PCR and protein-ligand docking led to the identification of an acyltransferases, contributing to the final structure of P-II.

A cluster of Ankyrin and Ankyrin-TPR repeat genes is associated with panicle branching diversity in rice

The number of grains per panicle is an important yield-related trait in cereals which depends in part on panicle branching complexity. One component of this complexity is the number of secondary branches per panicle. Previously, a GWAS site associated with secondary branch and spikelet numbers per panicle in rice was identified. Here we combined gene capture, bi-parental genetic population analysis, expression profiling and transgenic approaches in order to investigate the functional significance of a cluster of 6 ANK and ANK-TPR genes within the QTL. Four of the ANK and ANK-TPR genes present a differential expression associated with panicle secondary branch number in contrasted accessions. These differential expression patterns correlate in the different alleles of these genes with specific deletions of potential cis-regulatory sequences in their promoters. Two of these genes were confirmed through functional analysis as playing a role in the control of panicle architecture. Our findings indicate that secondary branching diversity in the rice panicle is governed in part by differentially expressed genes within this cluster encoding ANK and ANK-TPR domain proteins that may act as positive or negative regulators of panicle meristem’s identity transition from indeterminate to determinate state.

Grain yield is one of the most important indexes in rice breeding, which is controlled in part by panicle branching complexity. A new QTL with co-location of spikelet number (SpN) and secondary branch number (SBN) traits was identified by genome-wide association study in a Vietnamese rice landrace panel. A set of four Ankyrin and Tetratricopeptide repeat domain-encoding genes was identified from this QTL based on their difference of expression levels between two contrasted haplotypes for the SpN and SBN traits. The differential expression is correlated with deletions in the promoter regions of these genes. Two of the genes act as negative regulators of the panicle meristem’s identity transition from indeterminate to determinate state while the other two act as positive regulators of this meristem fate transition. Based on the different phenotypes between overexpressed and mutant plants, two of these genes were confirmed as playing a role in the control of panicle architecture. These findings can be directly used to assist selection for grain yield improvement.

Genomics, expression, and function analyses of XB3 family genes in cotton

XANTHOMONAS RESISTANCE 21-binding protein3 (XB3) is the first characterized XA21 interacting protein required for plant immunity. We isolated GhXB32A that is similar to XBAT32 and was induced during inoculation of Verticillium dahliae in cotton. 32 putative XB3 family genes were identified in G. hirsutum, G. arboreum, and G. raimondii. Cis-Acting elements related to growth, stresses, and phytohormone were detected in the promoter regions. GhXB3s were ubiquitously expressed in different cotton tissues with different patterns. Most GhXB3s were down-regulated by cold stress, but up-regulated by heat, salt, PEG, V. dahliae, ethylene, and some were up-regulated by SA or MeJA. Silencing GhXB32A and GhXB32D greatly improved resistance to Verticillium wilt, while silencing GhXB35A(D) or GhXB37A(D) made them more susceptible to V. dahliae. The interacting proteins of GhXB32A and GhXB32D were functionally enriched in response to abiotic and/or biotic stresses, and photosynthesis. XB3 family genes are potential stress resistance genes for cotton improvement.

The Ankyrin-Repeat Gene GmANK114 Confers Drought and Salt Tolerance in Arabidopsis and Soybean

Ankyrin repeat (ANK) proteins are essential in cell growth, development, and response to hormones and environmental stresses. In the present study, 226 ANK genes were identified and classified into nine subfamilies according to conserved domains in the soybean genome (Glycine max L.). Among them, the GmANK114 was highly induced by drought, salt, and abscisic acid. The GmANK114 encodes a protein that belongs to the ANK-RF subfamily containing a RING finger (RF) domain in addition to the ankyrin repeats. Heterologous overexpression of GmANK114 in transgenic Arabidopsis improved the germination rate under drought and salt treatments compared to wild-type. Homologous overexpression of GmANK114 improved the survival rate under drought and salt stresses in transgenic soybean hairy roots. In response to drought or salt stress, GmANK114 overexpression in soybean hairy root showed higher proline and lower malondialdehyde contents, and lower H2O2 and O2- contents compared control plants. Besides, GmANK114 activated transcription of several abiotic stress-related genes, including WRKY13, NAC11, DREB2, MYB84, and bZIP44 under drought and salt stresses in soybean. These results provide new insights for functional analysis of soybean ANK proteins and will be helpful for further understanding how ANK proteins in plants adapt to abiotic stress.

The ankyrin repeat gene family in Capsicum spp: Genome-wide survey, characterization and gene expression profile

The ankyrin (ANK) repeat protein family is largely distributed across plants and has been found to participate in multiple processes such as plant growth and development, hormone response, response to biotic and abiotic stresses. It is considered as one of the major markers of capsaicin content in pepper fruits. In this study, we performed a genome-wide identification and expression analysis of genes encoding ANK proteins in three Capsicum species: Capsicum baccatum, Capsicum annuum and Capsicum chinense. We identified a total of 87, 85 and 96 ANK genes in C. baccatum, C. annuum and C. chinense genomes, respectively. Next, we performed a comprehensive bioinformatics analysis of the Capsicum ANK gene family including gene chromosomal localization, Cis-elements, conserved motif identification, intron/exon structural patterns and gene ontology classification as well as profile expression. Phylogenetic and domain organization analysis grouped the Capsicum ANK gene family into ten subfamilies distributed across all 12 pepper chromosomes at different densities. Analysis of the expression of ANK genes in leaf and pepper fruits suggested that the ANKs have specific expression patterns at various developmental stages in placenta tissue. Our results provide valuable information for further studies of the evolution, classification and putative functions of ANK genes in pepper.

Genome-wide identification and transcriptome profiling reveal that E3 ubiquitin ligase genes relevant to ethylene, auxin and abscisic acid are differentially expressed in the fruits of melting flesh and stony hard peach varieties

Background

Ubiquitin ligases (E3) are the enzymes in the ubiquitin/26S proteasome pathway responsible for targeting proteins to the degradation pathway and play major roles in multiple biological activities. However, the E3 family and their functions are yet to be identified in the fruit of peach.

Results

In this study, genome-wide identification, classification and characterization of the E3 ligase genes within the genome of peach (Prunus persica) was carried out. In total, 765 E3 (PpE3) ligase genes were identified in the peach genome. The PpE3 ligase genes were divided into eight subfamilies according to the presence of known functional domains. The RBX subfamily was not detected in peach. The PpE3 ligase genes were not randomly distributed among the 8 chromosomes, with a greater concentration on the longer chromosomes. The primary mode of gene duplication of the PpE3 ligase genes was dispersed gene duplication (DSD). Four subgroups of the BTB subfamily never characterized before were newly identified in peach, namely BTBAND, BTBBL, BTBP and BTBAN. The expression patterns of the identified E3 ligase genes in two peach varieties that display different types of fruit softening (melting flesh, MF, and stony hard, SH) were analyzed at 4 different stages of ripening using Illumina technology. Among the 765 PpE3 ligase genes, 515 (67.3%) were expressed (FPKM > 1) in the fruit of either MF or SH during fruit ripening. In same-stage comparisons, 231 differentially expressed genes (DEGs) were identified between the two peach cultivars. The number of DEGs in each subfamily varied. Most DEGs were members of the BTB, F-box, U-box and RING subfamilies. PpE3 ligase genes predicted to be involved in ethylene, auxin, or ABA synthesis or signaling and DNA methylation were differentially regulated. Eight PpE3 ligase genes with possible roles in peach flesh texture and fruit ripening were discussed.

Conclusions

The results of this study provide useful information for further understanding the functional roles of the ubiquitin ligase genes in peach. The findings also provide the first clues that E3 ligase genes may function in the regulation of peach ripening.

Identification and characterization of maize ACD6-like gene reveal ZmACD6 as the maize orthologue conferring resistance to Ustilago maydis

Enhancing broad-spectrum resistance is a major goal of crop breeding. However, broad-spectrum resistance has not been thoroughly investigated, and its underlying molecular mechanisms remain elusive. In the model plant Arabidopsis (Arabidopsis thaliana), ACCELERATED CELL DEATH6 (ACD6) is a key component of broad-spectrum resistance that acts in a positive feedback loop with salicylic acid (SA) to regulate multiple pattern recognition receptors. However, the role of ACD6 in disease resistance in crop plants is unclear. Here, we show that the transcript of ANK23, one of the 15 ACD6-like genes in maize (Zea mays), is induced by SA and by infection with the pathogenic fungus Ustilago maydis. Heterologous expression of ANK23 restored disease resistance in the Arabidopsis mutant acd6-2. We show that ANK23 is a maize ortholog of ACD6 and therefore rename ANK23 as ZmACD6. Furthermore, using CRISPR/Cas9, we generated ZmACD6 knockout maize plants, which are more susceptible to U. maydis than wild-type plants. We also identified a maize line (SC-9) with relatively high ZmACD6 expression levels from a diverse natural maize population. SC-9 has increased disease resistance to U. maydis and defense activation, suggesting a practical approach to cultivate elite varieties with enhanced disease resistance.

Genome-wide characterization of the ankyrin repeats gene family under salt stress in soybean

Ankyrin repeats (ANK) gene family are common in diverse organisms and play important roles in cell growth, development and response to environmental stresses. Recently, genome-wide identification and evolutionary analyses of the ANK gene family have been carried out in Arabidopsis, rice and maize. However, little is known about the ANK genes in the whole soybean genome. In this study, we described the identification and structural characterization of 162ANK genes in soybean (GmANK). Then, comprehensive bioinformatics analyses of GmANK genes family were performed including gene locus, phylogenetic, domain composition analysis, chromosomal localization and expression profiling. Domain composition analyses showed that GmANK proteins formed eleven subfamilies in soybean. In sicilo expression analysis of these GmANK genes demonstrated that GmANK genes show a diverse/various expression pattern, suggesting that functional diversification of GmANK genes family. Based on digital gene expression profile (DGEP) data between cultivated soybean and wild type under salt treatment, some GmANKs related to salt/drought response were investigated. Moreover, the expression pattern and subcellular localization of GmANK6 were performed. The results will provide important clues to explore ANK genes expression and function in future studies in soybean.

Analyses of Physcomitrella patens Ankyrin Repeat Proteins by Computational Approach

Ankyrin (ANK) repeat containing proteins are evolutionary conserved and have functions in crucial cellular processes like cell cycle regulation and signal transduction. In this study, through an entirely in silico approach using the first release of the moss genome annotation, we found that at least 54 ANK proteins are present in P. patens. Based on their differential domain composition, the identified ANK proteins were classified into nine subfamilies. Comparative analysis of the different subfamilies of ANK proteins revealed that P. patens contains almost all the known subgroups of ANK proteins found in the other angiosperm species except for the ones having the TPR domain. Phylogenetic analysis using full length protein sequences supported the subfamily classification where the members of the same subfamily almost always clustered together. Synonymous divergence (dS) and nonsynonymous divergence (dN) ratios showed positive selection for the ANK genes of P. patens which probably helped them to attain significant functional diversity during the course of evolution. Taken together, the data provided here can provide useful insights for future functional studies of the proteins from this superfamily as well as comparative studies of ANK proteins.

VdNUC-2, the Key Regulator of Phosphate Responsive Signaling Pathway, Is Required for Verticillium dahliae Infection

In fungal cells, a phosphate (Pi) responsive signaling and metabolism (PHO) pathway regulates Pi-homeostasis. NUC-2/PHO81 and its homologs are one of the most important components in the regulation pathway. In soil-borne phytopathogenic fungus Verticillium dahliae, we identified a Neurospora crassa nuc-2 homolog gene VdNUC-2. VdNUC-2 is composed of 1,018 amino acids, and is highly conserved in tested filamentous fungi. Under conditions of Pi-starvation, compared with the wild-type strain and ectopic complementation strains, the VdNUC-2 knocked out mutants exhibited reduced radial growth, decreased production of conidia and microsclerotia, and were more sensitive to hydrogen peroxide stress. The virulence of VdNUC-2 defective mutants was significantly compromised, and that was unable to be restored by exogenous application of extra Pi. Additionally, the deletion mutants of VdNUC-1, a key transcription factor gene positively controlled by VdNUC-2 in the PHO pathway, showed the similar cultural phenotypes as VdNUC-2 mutants when both of them grew in Pi-limited conditions. However, the virulence of VdNUC-1 mutants was comparable to the wild-type strain. These evidences indicated that the virulence reduction in VdNUC-2 mutants is not due to the interruptions in the PHO pathway or the disturbance of Pi-homeostasis in V. dahliae cytoplasm. VdNUC-2 is not only a crucial gene in the PHO pathway in V. dahliae, but also is required for the full virulence during host-infection.

Expansion and Function of Repeat Domain Proteins During Stress and Development in Plants

The recurrent repeats having conserved stretches of amino acids exists across all domains of life. Subsequent repetition of single sequence motif and the number and length of the minimal repeating motifs are essential characteristics innate to these proteins. The proteins with tandem peptide repeats are essential for providing surface to mediate protein-protein interactions for fundamental biological functions. Plants are enriched in tandem repeat containing proteins typically distributed into various families. This has been assumed that the occurrence of multigene repeats families in plants enable them to cope up with adverse environmental conditions and allow them to rapidly acclimatize to these conditions. The evolution, structure, and function of repeat proteins have been studied in all kingdoms of life. The presence of repeat proteins is particularly profuse in multicellular organisms in comparison to prokaryotes. The precipitous expansion of repeat proteins in plants is presumed to be through internal tandem duplications. Several repeat protein gene families have been identified in plants. Such as Armadillo (ARM), Ankyrin (ANK), HEAT, Kelch-like repeats, Tetratricopeptide (TPR), Leucine rich repeats (LRR), WD40, and Pentatricopeptide repeats (PPR). The structure and functions of these repeat proteins have been extensively studied in plants suggesting a critical role of these repeating peptides in plant cell physiology, stress and development. In this review, we illustrate the structural, functional, and evolutionary prospects of prolific repeat proteins in plants.

OsNRAMP5 contributes to manganese translocation and distribution in rice shoots

Manganese (Mn) is an essential micronutrient for plants playing an important role in many physiological functions. OsNRAMP5 is a major transporter responsible for Mn and cadmium uptake in rice, but whether it is involved in the root-to-shoot translocation and distribution of these metals is unknown. In this work, OsNRAMP5 was found to be highly expressed in hulls. It was also expressed in leaves but the expression level decreased with leaf age. High-magnification observations revealed that OsNRAMP5 was enriched in the vascular bundles of roots and shoots especially in the parenchyma cells surrounding the xylem. The osnramp5 mutant accumulated significantly less Mn in shoots than the wild-type plants even at high levels of Mn supply. Furthermore, a high supply of Mn could compensate for the loss in the root uptake ability in the mutant, but not in the root-to-shoot translocation of Mn, suggesting that the absence of OsNRAMP5 reduces the transport of Mn from roots to shoots. The results suggest that OsNRAMP5 plays an important role in the translocation and distribution of Mn in rice plants in addition to its role in Mn uptake.

Genome-wide identification and expression profiling of ankyrin-repeat gene family in maize

Members of the ankyrin repeats (ANK) gene family encode ANK domain that are common in diverse organisms and play important roles in cell growth and development, such as cell-cell signal transduction and cell cycle regulation. Recently, genome-wide identification and evolutionary analyses of the ANK gene family have been carried out in Arabidopsis and rice. However, little is known regarding the ANK genes in the entire maize genome. In this study, we described the identification and structural characterization of 71 ANK genes in maize (ZmANK). Then, comprehensive bioinformatics analyses of ZmANK genes family were performed including phylogenetic, domain and motif analysis, chromosomal localization, intron/exon structural patterns, gene duplications and expression profiling. Domain composition analyses showed that ZmANK genes formed ten subfamilies. Five tandem duplications and 14 segmental duplications were identified in ZmANK genes. Furthermore, we took comparative analysis of the total ANK gene family in Arabidopsis, rice and maize, ZmANKs were more closely paired with OsANKs than with AtANKs. At last, expression profile analyses were performed. Forty-one members of ZmANK genes held EST sequences records. Semi-quantitative expression and microarray data analysis of these 41 ZmANK genes demonstrated that ZmANK genes exhibit a various expression pattern, suggesting that functional diversification of ZmANK genes family. The results will present significant insights to explore ANK genes expression and function in future studies in maize.

Silicon era of carbon-based life: application of genomics and bioinformatics in crop stress research

Abiotic and biotic stresses lead to massive reprogramming of different life processes and are the major limiting factors hampering crop productivity. Omics-based research platforms allow for a holistic and comprehensive survey on crop stress responses and hence may bring forth better crop improvement strategies. Since high-throughput approaches generate considerable amounts of data, bioinformatics tools will play an essential role in storing, retrieving, sharing, processing, and analyzing them. Genomic and functional genomic studies in crops still lag far behind similar studies in humans and other animals. In this review, we summarize some useful genomics and bioinformatics resources available to crop scientists. In addition, we also discuss the major challenges and advancements in the "-omics" studies, with an emphasis on their possible impacts on crop stress research and crop improvement.

Superfamily of ankyrin repeat proteins in tomato

The ankyrin repeat (ANK) protein family plays a crucial role in plant growth and development and in response to biotic and abiotic stresses. However, no detailed information concerning this family is available for tomato (Solanum lycopersicum) due to the limited information on whole genome sequences. In this study, we identified a total of 130 ANK genes in tomato genome (SlANK), and these genes were distributed across all 12 chromosomes at various densities. And chromosomal localizations of SlANK genes indicated 25 SlANK genes were involved in tandem duplications. Based on their domain composition, all of the SlANK proteins were grouped into 13 subgroups. A combined phylogenetic tree was constructed with the aligned SlANK protein sequences. This tree revealed that the SlANK proteins comprise five major groups. An analysis of the expression profiles of SlANK genes in tomato in different tissues and in response to stresses showed that the SlANK proteins play roles in plant growth, development and stress responses. To our knowledge, this is the first report of a genome-wide analysis of the tomato ANK gene family. This study provides valuable information regarding the classification and putative functions of SlANK genes in tomato.

Functional analysis and expressional characterization of rice ankyrin repeat-containing protein, OsPIANK1, in basal defense against Magnaporthe oryzae attack

The ankyrin repeat-containing protein gene OsPIANK1 (AK068021) in rice (Oryza sativa L.) was previously shown to be upregulated following infection with the rice leaf blight pathogen Xanthomonas oryzae pv oryzae (Xoo). In this study, we further characterized the role of OsPIANK1 in basal defense against Magnaporthe oryzae (M.oryzae) by 5' deletion analysis of its promoter and overexpression of the gene. The promoter of OsPIANK1 with 1,985 bps in length was sufficient to induce the OsPIANK1 response to inoculation with M.oryzae and to exogenous application of methyl jasmonate (MeJA) or salicylic acid (SA), but not to exogenous application of abscisic acid (ABA). A TCA-element present in the region between -563 bp and -249 bp may be responsible for the OsPIANK1 response to both M.oryzae infection and exogenous SA application. The JERE box, CGTCA-box, and two MYB binding sites locating in the region between -1985 bp and -907 bp may be responsible for the response of OsPIANK1 to exogenous MeJA. OsPIANK1 expression was upregulated after inoculation with M.oryzae and after treatment with exogenous SA and MeJA. Overexpression of OsPIANK1 enhanced resistance of rice to M.oryzae, although it did not confer complete resistance. The enhanced resistance to M.oryzae was accompanied by enhanced transcriptional expression of SA- and JA-dependent genes such as NH1, WKRY13, PAL, AOS2, PR1b, and PR5. This evidence suggests that OsPIANK1 acted as a positive regulator in rice basal defense mediated by SA- and JA-signaling pathways.

Global analysis of ankyrin repeat domain C3HC4-type RING finger gene family in plants

Ankyrin repeat (ANK) C3HC4-type RING finger (RF) genes comprise a large family in plants and play important roles in various physiological processes of plant life. In this study, we identified 187 ANK C3HC4-type RF proteins from 29 species with complete genomes and named the ANK C3HC4-type RF proteins the XB3-like proteins because they are structurally related to the rice (Oryza sativa) XB3. A phylogenetic relationship analysis suggested that the XB3-like genes originated from ferns, and the encoded proteins fell into 3 major groups. Among these groups, we found that the spacing between the metal ligand position 6 and 7, and the conserved residues, which was in addition to the metal ligand amino acids, in the C3HC4-type RF were different. Using a wide range of protein structural analyses, protein models were established, and all XB3-like proteins were found to contain two to seven ANKs and a C3HC4-type RF. The microarray data for the XB3-like genes of Arabidopsis, Oryza sative, Zea mays and Glycine max revealed that the expression of XB3-like genes was in different tissues and during different life stages. The preferential expression of XB3-like genes in specified tissues and the response to phytohormone and abiotic stress treatments of Arabidopsis and Zea mays not only confirmed the microarray analysis data but also demonstrated that the XB3-like proteins play roles in plant growth and development as well as in stress responses. Our data provide a very useful reference for the identification and functional analysis of members of this gene family and also provide a new method for the genome-wide analysis of gene families.

In silico analysis reveals the presence of a large number of Ankyrin repeat containing proteins in Ectocarpus siliculosus

Proteins with Ankyrin repeat motifs (ANK) are found to be associated with diverse biological processes and molecular functions in most of the studied organisms. Several studies have been done on the ANK-motif containing proteins of various model species, but similar studies on their counterparts in brown algae are not available. In this study, we have identified a total of 1,372 ankyrin repeats in 339 proteins of the model brown algae Ectocarpus siliculosus and the consensus sequence of the ANK repeats was determined. The proteins were classified into eight different subfamilies depending on their structural diversity. The data provided in this study may provide useful basis for future reverse genetics analysis of the members of this family.

Interaction between a plasma membrane-localized ankyrin-repeat protein ITN1 and a nuclear protein RTV1

The increased tolerance to NaCl 1 (ITN1) protein is a plasma membrane (PM)-localized protein involved in responses to NaCl stress in Arabidopsis. The predicted structure of ITN1 is composed of multiple transmembrane regions and an ankyrin-repeat domain that is known to mediate protein-protein interactions. To elucidate the molecular functions of ITN1, we searched for interacting partners using a yeast two-hybrid assay, and a nuclear-localized DNA-binding protein, RTV1, was identified as a candidate. Bimolecular fluorescence complementation analysis revealed that RTV1 interacted with ITN1 at the PM and nuclei in vivo. RTV1 tagged with red fluorescent protein localized to nuclei and ITN1 tagged with green fluorescent protein localized to PM; however, both proteins localized to both nuclei and the PM when co-expressed. These findings suggest that RTV1 and ITN1 regulate the subcellular localization of each other.

Rice functional genomics research: progress and implications for crop genetic improvement

Rice is a staple food crop and has become a reference of monocot plant for functional genomic research. With the availability of high quality rice genome sequence, there has been rapid accumulation of functional genomic resources, including: large mutant libraries by T-DNA insertion, transposon tagging, and chemical mutagenesis; global expression profiles of the genes in the entire life cycle of rice growth and development; full-length cDNAs for both indica and japonica rice; sequences from resequencing large numbers of diverse germplasm accessions. Such resource development has greatly accelerated gene cloning. By the end of 2010, over 600 genes had been cloned using various methods. Many of the genes control agriculturally useful traits such as yield, grain quality, resistances to biotic and abiotic stresses, and nutrient-use efficiency, thus have potential utility in crop genetic improvement. This review was aimed to provide a comprehensive summary of such progress. We also presented our perspective for future studies.

Genomic survey, characterization and expression profile analysis of the peptide transporter family in rice (Oryza sativa L.)

BACKGROUND

Peptide transporter (PTR) family whose member can transport di-/tripeptides and nitrate is important for plant growth and development. Although the rice (Oryza sativa L.) genome has been sequenced for a few years, a genomic survey, characterization and expression profile analysis of the PTR family in this species has not been reported.

RESULTS

In this study, we report a comprehensive identification, characterization, phylogenetic and evolutionary analysis of 84 PTR family members in rice (OsPTR) as well as their whole-life expression patterns. Chromosomal distribution and sequence analysis indicate that nearly 70% of OsPTR members are involved in the tandem and segmental duplication events. It suggests that genome duplication might be a major mechanism for expansion of this family. Highly conserved motifs were identified in most of the OsPTR members. Meanwhile, expression profile of OsPTR genes has been analyzed by using Affymetrix rice microarray and real-time PCR in two elite hybrid rice parents, Minghui 63 and Zhenshan 97. Seven genes are found to exhibit either preferential or tissue-specific expression during different development stages of rice. Under phytohormone (NAA, GA3 and KT) and light/dark treatments, 14 and 17 OsPTR genes are differentially expressed respectively. Ka/Ks analysis of the paralogous OsPTR genes indicates that purifying selection plays an important role in function maintenance of this family.

CONCLUSION

These investigations add to our understanding of the importance of OsPTR family members and provide useful reference for selecting candidate genes for functional validation studies of this family in rice.

A dynamic gene expression atlas covering the entire life cycle of rice

Growth and development of a plant are controlled by programmed expression of suits of genes at the appropriate time, tissue and abundance. Although genomic resources have been developed rapidly in recent years in rice, a model plant for cereal genome research, data of gene expression profiling are still insufficient to relate the developmental processes to transcriptomes, leaving a large gap between the genome sequence and phenotype. In this study, we generated genome-wide expression data by hybridizing 190 Affymetrix GeneChip Rice Genome Arrays with RNA from 39 tissues collected throughout the life cycle of the rice plant from two varieties, Zhenshan 97 and Minghui 63. Analyses of the global transcriptomes revealed many interesting features of dynamic patterns of gene expression across the tissues and stages. In total, 38 793 probe sets were detected as expressed and 69% of the expressed transcripts showed significantly variable expression levels among tissues/organs. We found that similarity of transcriptomes among organs corresponded well to their developmental relatedness. About 5.2% of the expressed transcripts showed tissue-specific expression in one or both varieties and 22.7% of the transcripts exhibited constitutive expression including 19 genes with high and stable expression in all the tissues. This dataset provided a versatile resource for plant genomic research, which can be used for associating the transcriptomes to the developmental processes, understanding the regulatory network of these processes, tracing the expression profile of individual genes and identifying reference genes for quantitative expression analyses.