Evolutionary History of the Glycoside Hydrolase 3 (GH3) Family Based on the Sequenced Genomes of 48 Plants and Identification of Jasmonic Acid-Related GH3 Proteins in Solanum tuberosum

Comparative Analysis of Hulless Barley Transcriptomes to Regulatory Effects of Phosphorous Deficiency

Hulless barley is a cold-resistant crop widely planted in the northwest plateau of China. It is also the main food crop in this region. Phosphorus (P), as one of the important essential nutrient elements, regulates plant growth and defense. This study aimed to analyze the development and related molecular mechanisms of hulless barley under P deficiency and explore the regulatory genes so as to provide a basis for subsequent molecular breeding research. Transcriptome analysis was performed on the root and leaf samples of hulless barley cultured with different concentrations of KH2PO4 (1 mM and 10 μM) Hoagland solution. A total of 46,439 genes were finally obtained by the combined analysis of leaf and root samples. Among them, 325 and 453 genes had more than twofold differences in expression. These differentially expressed genes (DEGs) mainly participated in the abiotic stress biosynthetic process through Gene Ontology prediction. Moreover, the Kyoto Encyclopedia of Genes and Genomes showed that DEGs were mainly involved in photosynthesis, plant hormone signal transduction, glycolysis, phenylpropanoid biosynthesis, and synthesis of metabolites. These pathways also appeared in other abiotic stresses. Plants initiated multiple hormone synergistic regulatory mechanisms to maintain growth under P-deficient conditions. Transcription factors (TFs) also proved these predictions. The enrichment of ARR-B TFs, which positively regulated the phosphorelay-mediated cytokinin signal transduction, and some other TFs (AP2, GRAS, and ARF) was related to plant hormone regulation. Some DEGs showed different values in their FPKM (fragment per kilobase of transcript per million mapped reads), but the expression trends of genes responding to stress and phosphorylation remained highly consistent. Therefore, in the case of P deficiency, the first response of plants was the expression of stress-related genes. The effects of this stress on plant metabolites need to be further studied to improve the relevant regulatory mechanisms so as to further understand the importance of P in the development and stress resistance of hulless barley.

Evolutionary Analysis of the Melon (Cucumis melo L.) GH3 Gene Family and Identification of GH3 Genes Related to Fruit Growth and Development

The indole-3-acetic acid (IAA) auxin is an important endogenous hormone that plays a key role in the regulation of plant growth and development. In recent years, with the progression of auxin-related research, the function of the Gretchen Hagen 3 (GH3) gene has become a prominent research topic. However, studies focusing on the characteristics and functions of melon GH3 family genes are still lacking. This study presents a systematic identification of melon GH3 gene family members based on genomic data. The evolution of melon GH3 family genes was systematically analyzed by means of bioinformatics, and the expression patterns of the GH3 family genes in different melon tissues during different fruit developmental stages and with various levels of 1-naphthaleneacetic acid (NAA) induction were analyzed with transcriptomics and RT-qPCR. The melon genome contains 10 GH3 genes distributed across seven chromosomes, and most of these genes are expressed in the plasma membrane. According to evolutionary analysis and the number of GH3 family genes, these genes can be divided into three subgroups, and they have been conserved throughout the evolution of melon. The melon GH3 gene has a wide range of expression patterns across distinct tissue types, with expression generally being higher in flowers and fruit. Through promoter analysis, we found that most cis-acting elements contained light- and IAA-responsive elements. Based on the RNA-seq and RT-qPCR analyses, it can be speculated that CmGH3-5, CmGH3-6 and CmGH3-7 may be involved in the process of melon fruit development. In conclusion, our findings suggest that the GH3 gene family plays an important role in the development of melon fruit. This study provides an important theoretical basis for further research on the function of the GH3 gene family and the molecular mechanism underlying the development of melon fruit.

Toxic mechanism of two cyanobacterial volatiles β-cyclocitral and β-ionone on the photosynthesis in duckweed by altering gene expression

Volatile organic compounds (VOCs) promote cyanobacteria dominating eutrophicated waters, with aquatic plant decrease and even disappearance. To uncover the toxic mechanism of cyanobacterial VOCs on aquatic plants, we investigated the growth, photosynthetic pigment levels, photosynthetic abilities and related gene expression in duckweed treated with β-cyclocitral and β-ionone, 2 main components in the VOCs. The levels of chlorophylls and carotenoids gradually declined with raising the concentration of the 2 compounds and prolonging the treatment time. Their decline should result from the down-regulation of 8 genes associated with photosynthetic pigment biosynthesis and up-regulation of 2 genes involved in carotenoid degradation. The reduction was also found in the photosystem II (PSII) efficiency and O₂ evolution rate, which should result from the lowered photosynthetic pigment levels and down-regulation of 38 genes related with photosynthetic process. The frond numbers, total frond area and fresh weight gradually decreased with raising the 2 compound concentration, which may result from the lowered photosynthetic abilities as well as down-regulated expression of 7 genes associated with growth-promoting hormone biosynthesis and signal transduction. It can be speculated that cyanobacterial VOCs may poison aquatic plants by lowering the photosynthesis and growth through altering related gene expression.

Biochemical characterization of a novel glucose-tolerant GH3 β-glucosidase (Bgl1973) from Leifsonia sp. ZF2019

Beta-glucosidase (Bgl) is an enzyme with considerable food, beverage, and biofuel processing potential. However, as many Bgls are inhibited by their reaction end product glucose, their industrial applications are greatly limited. In this study, a novel Bgl gene (Bgl1973) was cloned from Leifsonia sp. ZF2019 and heterologously expressed in E. coli. Sequence analysis and structure modeling revealed that Bgl1973 was 748 aa, giving it a molecular weight of 78 kDa, and it showed high similarity with the glycoside hydrolase 3 (GH3) family Bgls with which its active site residues were conserved. By using pNPGlc (p-nitrophenyl-β-D-glucopyranoside) as substrate, the optimum temperature and pH of Bgl1973 were shown to be 50 °C and 7.0, respectively. Bgl1973 was insensitive to most metal ions (12.5 mM), 1% urea, and even 0.1% Tween-80. This enzyme maintained 60% of its original activity in the presence of 20% NaCl, demonstrating its excellent salt tolerance. Furthermore, it still had 83% residual activity in 1 M of glucose, displaying its outstanding glucose tolerance. The K_m, V_max, and k_cat of Bgl1973 were 0.22 mM, 44.44 μmol/min mg, and 57.78 s^-1, respectively. Bgl1973 had a high specific activity for pNPGlc (19.10 ± 0.59 U/mg) and salicin (20.43 ± 0.92 U/mg). Furthermore, molecular docking indicated that the glucose binding location and the narrow and deep active channel geometry might contribute to the glucose tolerance of Bgl1973. Our results lay a foundation for the studying of this glucose-tolerant β-glucosidase and its applications in many industrial settings. KEY POINTS: • A novel β-glucosidase from GH3 was obtained from Leifsonia sp. ZF2019. • Bgl1973 demonstrated excellent glucose tolerance. • The glucose tolerance of Bgl1973 was explained using molecular docking analysis.

In Silico Identification and Characterization of B12D Family Proteins in Viridiplantae

B12D family proteins are transmembrane proteins that contain the B12D domain involved in membrane trafficking. Plants comprise several members of the B12D family, but these members’ numbers and specific functions are not determined. This study aims to identify and characterize the members of B12D protein family in plants. Phytozome database was retrieved for B12D proteins from 14 species. The total 66 B12D proteins were analyzed in silico for gene structure, motifs, gene expression, duplication events, and phylogenetics. In general, B12D proteins are between 86 and 98 aa in length, have 2 or 3 exons, and comprise a single transmembrane helix. Motif prediction and multiple sequence alignment show strong conservation among B12D proteins of 11 flowering plants species. Despite that, the phylogenetic tree revealed a distinct cluster of 16 B12D proteins that have high conservation across flowering plants. Motif prediction revealed 41 aa motif conserved in 58 of the analyzed B12D proteins similar to the bZIP motif, confirming that in the predicted biological process and molecular function, B12D proteins are DNA-binding proteins. Cis-regulatory elements screening in putative B12D promoters found various responsive elements for light, abscisic acid, methyl jasmonate, cytokinin, drought, and heat. Despite that, there is specific elements for cold stress, cell cycle, circadian, auxin, salicylic acid, and gibberellic acid in the promoter of a few B12D genes indicating for functional diversification for B12D family members. The digital expression shows that B12D genes of Glycine max have similar expression patterns consistent with their clustering in the phylogenetic tree. However, the expression of B12D genes of Hordeum vulgure appears inconsistent with their clustering in the tree. Despite the strong conservation of the B12D proteins of Viridiplantae, gene association analysis, promoter analysis, and digital expression indicate different roles for the members of the B12D family during plant developmental stages.

Bulk RNA-Seq Analysis Reveals Differentially Expressed Genes Associated with Lateral Branch Angle in Peanut

Lateral branch angle (LBA), or branch habit, is one of the most important agronomic traits in peanut. To date, the underlying molecular mechanisms of LBA have not been elucidated in peanut. To acquire the differentially expressed genes (DEGs) related to LBA, a TI population was constructed through the hybridization of a bunch-type peanut variety Tifrunner and prostrate-type Ipadur. We report the identification of DEGs related to LBA by sequencing two RNA pools, which were composed of 45 F₃ lines showing an extreme opposite bunch and prostrate phenotype. We propose to name this approach Bulk RNA-sequencing (BR-seq) as applied to several plant species. Through BR-seq analysis, a total of 3083 differentially expressed genes (DEGs) were identified, including 13 gravitropism-related DEGs, 22 plant hormone-related DEGs, and 55 transcription factors-encoding DEGs. Furthermore, we also identified commonly expressed alternatively spliced (AS) transcripts, of which skipped exon (SE) and retained intron (RI) were most abundant in the prostrate and bunch-type peanut. AS isoforms between prostrate and bunch peanut highlighted important clues to further understand the post-transcriptional regulatory mechanisms of branch angle regulation. Our findings provide not only important insights into the landscape of the regulatory pathway involved in branch angle formation but also present practical information for peanut molecular breeding in the future.

Molecular and functional characterization of a jasmonate resistant gene of wheat (Triticum aestivum L.)

Jasmonates play important roles in several plant developmental processes and responses to biotic and abiotic stresses. This study identified a gene encoding jasmonate resistant 1 (JAR1) protein that catalyzes the production of bioactive jasmonoyl-isoleucine (JA-Ile) from hexaploid wheat (Triticum aestivum L), designated as TaJAR1B. The nucleotide sequence of TaJAR1B and amino acid sequence of the corresponding protein exhibited high identity and similarity with other plant JAR1s. Feeding the culture of E. coli cells heterologously expressing TaJAR1B with jasmonic acid (JA) resulted in the production of JA-Ile, indicating the functionality of TaJAR1B in converting JA to JA-Ile. TaJAR1B was highly expressed in the internodes of adult plants and maturing seeds. Salt treatment induced the expression level of TaJAR1B in seedling tissues. Our results indicate that TaJAR1B encodes a functional JAR and is involved in the regulation of plant growth and developmental processes and response to salinity in wheat.

Changes in Gene Expression in Leaves of Cacao Genotypes Resistant and Susceptible to Phytophthora palmivora Infection

Black pod rot, caused by Phytophthora palmivora, is a devastating disease of Theobroma cacao L. (cacao) leading to huge losses for farmers and limiting chocolate industry supplies. To understand resistance responses of cacao leaves to P. palmivora, Stage 2 leaves of genotypes Imperial College Selection 1 (ICS1), Colección Castro Naranjal 51 (CCN51), and Pound7 were inoculated with zoospores and monitored for symptoms up to 48 h. Pound7 consistently showed less necrosis than ICS1 and CCN51 48 h after inoculation. RNA-Seq was carried out on samples 24 h post inoculation. A total of 24,672 expressed cacao genes were identified, and 2,521 transcripts showed induction in at least one P. palmivora-treated genotype compared to controls. There were 115 genes induced in the P. palmivora-treated samples in all three genotypes. Many of the differentially expressed genes were components of KEGG pathways important in plant defense signal perception (the plant MAPK signaling pathway, plant hormone signal transduction, and plant pathogen interactions), and plant defense metabolite biosynthesis (phenylpropanoid biosynthesis, α-linolenic acid metabolism, ethylene biosynthesis, and terpenoid backbone biosynthesis). A search of putative cacao resistance genes within the cacao transcriptome identified 89 genes with prominent leucine-rich repeat (LRR) domains, 170 protein kinases encoding genes, 210 genes with prominent NB-ARC domains, 305 lectin-related genes, and 97 cysteine-rich RK genes. We further analyzed the cacao leaf transcriptome in detail focusing on gene families-encoding proteins important in signal transduction (MAP kinases and transcription factors) and direct plant defense (Germin-like, ubiquitin-associated, lectin-related, pathogenesis-related, glutathione-S-transferases, and proteases). There was a massive reprogramming of defense gene processes in susceptible cacao leaf tissue after infection, which was restricted in the resistant genotype Pound7. Most genes induced in Pound7 were induced in ICS1/CCN51. The level of induction was not always proportional to the infection level, raising the possibility that genes are responding to infection more strongly in Pound7. There were also defense-associated genes constitutively differentially expressed at higher levels in specific genotypes, possibly providing a prepositioned defense. Many of the defense genes occur in blocks where members are constitutively expressed at different levels, and some members are induced by Ppal infection. With further study, the identified candidate genes and gene blocks may be useful as markers for breeding disease-resistant cacao genotypes against P. palmivora.

Physcomitrium patens Mutants in Auxin Conjugating GH3 Proteins Show Salt Stress Tolerance but Auxin Homeostasis Is Not Involved in Regulation of Oxidative Stress Factors

Salt stress is among the most challenging abiotic stress situations that a plant can experience. High salt levels do not only occur in areas with obvious salty water, but also during drought periods where salt accumulates in the soil. The moss Physcomitrium patens became a model for studying abiotic stress in non-vascular plants. Here, we show that high salt concentrations can be tolerated in vitro, and that auxin homeostasis is connected to the performance of P. patens under these stress conditions. The auxin levels can be regulated by conjugating IAA to amino acids by two members of the family of GH3 protein auxin amino acid-synthetases that are present in P. patens. Double GH3 gene knock-out mutants were more tolerant to high salt concentrations. Furthermore, free IAA levels were differentially altered during the time points investigated. Since, among the mutant lines, an increase in IAA on at least one NaCl concentration tested was observed, we treated wild type (WT) plants concomitantly with NaCl and IAA. This experiment showed that the salt tolerance to 100 mM NaCl together with 1 and 10 µM IAA was enhanced during the earlier time points. This is an additional indication that the high IAA levels in the double GH3-KO lines could be responsible for survival in high salt conditions. While the high salt concentrations induced several selected stress metabolites including phenols, flavonoids, and enzymes such as peroxidase and superoxide dismutase, the GH3-KO genotype did not generally participate in this upregulation. While we showed that the GH3 double KO mutants were more tolerant of high (250 mM) NaCl concentrations, the altered auxin homeostasis was not directly involved in the upregulation of stress metabolites.

A Role for Auxin in Triggering Lamina Outgrowth of Unifacial Leaves

A common morphological feature of typical angiosperms is the patterning of lateral organs along primary axes of asymmetry-a proximodistal, a mediolateral, and an adaxial-abaxial axis. Angiosperm leaves usually have distinct adaxial-abaxial identity, which is required for the development of a flat shape. By contrast, many unifacial leaves, consisting of only the abaxial side, show a flattened morphology. This implicates a unique mechanism that allows leaf flattening independent of adaxial-abaxial identity. In this study, we report a role for auxin in outgrowth of unifacial leaves. In two closely related unifacial-leaved species of Juncaceae, Juncus prismatocarpus with flattened leaves, and Juncus wallichianus with transversally radialized leaves, the auxin-responsive gene GLYCOSIDE HYDROLASE3 displayed spatially different expression patterns within leaf primordia. Treatment of J. prismatocarpus seedlings with exogenous auxin or auxin transport inhibitors, which disturb endogenous auxin distribution, eliminated leaf flatness, resulting in a transversally radialized morphology. These treatments did not affect the radialized morphology of leaves of J. wallichianus. Moreover, elimination of leaf flatness by these treatments accompanied dysregulated expression of genetic factors needed to specify the leaf central-marginal polarity in J. prismatocarpus. The findings imply that lamina outgrowth of unifacial leaves relies on proper placement of auxin, which might induce initial leaf flattening and subsequently act to specify leaf polarity, promoting further flattening growth of leaves.

Sedentary Plant-Parasitic Nematodes Alter Auxin Homeostasis via Multiple Strategies

Sedentary endoparasites such as cyst and root-knot nematodes infect many important food crops and are major agro-economical pests worldwide. These plant-parasitic nematodes exploit endogenous molecular and physiological pathways in the roots of their host to establish unique feeding structures. These structures function as highly active transfer cells and metabolic sinks and are essential for the parasites' growth and reproduction. Plant hormones like indole-3-acetic acid (IAA) are a fundamental component in the formation of these feeding complexes. However, their underlying molecular and biochemical mechanisms are still elusive despite recent advances in the field. This review presents a comprehensive overview of known functions of various auxins in plant-parasitic nematode infection sites, based on a systematic analysis of current literature. We evaluate multiple aspects involved in auxin homeostasis in plants, including anabolism, catabolism, transport, and signalling. From these analyses, a picture emerges that plant-parasitic nematodes have evolved multiple strategies to manipulate auxin homeostasis to establish a successful parasitic relationship with their host. Additionally, there appears to be a potential role for auxins other than IAA in plant-parasitic nematode infections that might be of interest to be further elucidated.

Genome-wide identification of GH3 genes in Brassica oleracea and identification of a promoter region for anther-specific expression of a GH3 gene

Background

The Gretchen Hagen 3 (GH3) genes encode acyl acid amido synthetases, many of which have been shown to modulate the amount of active plant hormones or their precursors. GH3 genes, especially Group III subgroup 6 GH3 genes, and their expression patterns in economically important B. oleracea var. oleracea have not been systematically identified.

Results

As a first step to understand regulation and molecular functions of Group III subgroup 6 GH3 genes, 34 GH3 genes including four subgroup 6 genes were identified in B. oleracea var. oleracea. Synteny found around subgroup 6 GH3 genes in B. oleracea var. oleracea and Arabidopsis thaliana indicated that these genes are evolutionarily related. Although expression of four subgroup 6 GH3 genes in B. oleracea var. oleracea is not induced by auxin, gibberellic acid, or jasmonic acid, the genes show different organ-dependent expression patterns. Among subgroup 6 GH3 genes in B. oleracea var. oleracea, only BoGH3.13–1 is expressed in anthers when microspores, polarized microspores, and bicellular pollens are present, similar to two out of four syntenic A. thaliana subgroup 6 GH3 genes. Detailed analyses of promoter activities further showed that BoGH3.13–1 is expressed in tapetal cells and pollens in anther, and also expressed in leaf primordia and floral abscission zones.

Conclusions

Sixty-two base pairs (bp) region (− 340 ~ − 279 bp upstream from start codon) and about 450 bp region (− 1489 to − 1017 bp) in BoGH3.13–1 promoter are important for expressions in anther and expressions in leaf primordia and floral abscission zones, respectively. The identified anther-specific promoter region can be used to develop male sterile transgenic Brassica plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07345-9.

Evolutionary history of the C-repeat binding factor/dehydration-responsive element-binding 1 (CBF/DREB1) protein family in 43 plant species and characterization of CBF/DREB1 proteins in Solanum tuberosum

Background

Plants are easily affected by temperature variations, and high temperature (heat stress) and low temperature (cold stress) will lead to poor plant development and reduce crop yields. Therefore, it is very important to identify resistance genes for improving the ability of plants to resist heat stress or cold stress by using modern biotechnology. Members of the C-repeat binding factor/Dehydration responsive element-binding 1 (CBF/DREB1) protein family are related to the stress resistance of many plant species. These proteins affect the growth and development of plants and play vital roles during environmental stress (cold, heat, drought, salt, etc.). In this study, we identified CBF/DREB1 genes from 43 plant species (including algae, moss, ferns, gymnosperms, angiosperms) by using bioinformatic methods to clarify the characteristics of the CBF/DREB1 protein family members and their functions in potato under heat and cold stresses.

Results

In this study, we identified 292 CBF/DREB1 proteins from 43 plant species. However, no CBF/DREB1 protein was found in algae, moss, ferns, or gymnosperms; members of this protein family exist only in angiosperms. Phylogenetic analysis of all the CBF/DREB1 proteins revealed five independent groups. Among them, the genes of group I do not exist in eudicots and are found only in monocots, indicating that these genes have a special effect on monocots. The analysis of motifs, gene duplication events, and the expression data from the PGSC website revealed the gene structures, evolutionary relationships, and expression patterns of the CBF/DREB1 proteins. In addition, analysis of the transcript levels of the 8 CBF/DREB1 genes in potato (Solanum tuberosum) under low-temperature and high-temperature stresses showed that these genes were related to temperature stresses. In particular, the expression levels of StCBF3 and StCBF4 in the leaves, stems, and roots significantly increased under high-temperature conditions, which suggested that StCBF3 and StCBF4 may be closely related to heat tolerance in potato.

Conclusion

Overall, members of the CBF/DREB1 protein family exist only in angiosperms and plays an important role in the growth and development of plants. In addition, the CBF/DREB1 protein family is related to the heat and cold resistance of potato. Our research revealed the evolution of the CBF/DREB1 family, and is useful for studying the precise functions of the CBF/DREB1 proteins when the plants are developing and are under temperature stress.

Evolutionary history of the heat shock protein 90 (Hsp90) family of 43 plants and characterization of Hsp90s in Solanum tuberosum

Heat shock protein 90 genes/proteins (Hsp90s) are related to the stress resistance found in various plant species. These proteins affect the growth and development of plants and have important effects on the plants under various stresses (cold, drought and salt) in the environment. In this study, we identified 334 Hsp90s from 43 plant species, and Hsp90s were found in all species. Phylogenetic tree and conserved domain database analysis of all Hsp90s showed three independent clades. The analysis of motifs, gene duplication events, and the expression data from PGSC website revealed the gene structures, evolution relationships, and expression patterns of the Hsp90s. In addition, analysis of the transcript levels of the 7 Hsp90s in potato (Solanum tuberosum) under low temperature and high temperature stresses showed that these genes were related to the temperature stresses. Especially StHsp90.2 and StHsp90.4, under high or low temperature conditions, the expression levels in leaves, stems, or roots were significantly up-regulated. Our findings revealed the evolution of the Hsp90s, which had guiding significance for further researching the precise functions of the Hsp90s.

Evolutionary significance of amino acid permease transporters in 17 plants from Chlorophyta to Angiospermae

Background

Nitrogen is an indispensable nutrient for plant growth. It is used and transported in the form of amino acids in living organisms. Transporting amino acids to various parts of plants requires relevant transport proteins, such as amino acid permeases (AAPs), which were our focus in this study.

Results

We found that 5 AAP genes were present in Chlorophyte species and more AAP genes were predicted in Bryophyta and Lycophytes. Two main groups were defined and group I comprised 5 clades. Our phylogenetic analysis indicated that the origin of clades 2, 3, and 4 is Gymnospermae and that these clades are closely related. The members of clade 1 included Chlorophyta to Gymnospermae. Group II, as a new branch consisting of non-seed plants, is first proposed in our research. Our results also indicated that the AAP family was already present in Chlorophyta and then expanded accompanying the development of vasculature. Concurrently, the AAP family experienced multiple duplication events that promoted the generation of new functions and differentiation of sub-functions.

Conclusions

Our findings suggest that the AAP gene originated in Chlorophyta, and some non-seed AAP genes clustered in one group. A second group, which contained plants of all evolutionary stages, indicated the evolution of AAPs. These new findings can be used to guide future research.

Old Town Roads: routes of auxin biosynthesis across kingdoms

Auxin is an important signaling molecule synthesized in organisms from multiple kingdoms of life, including land plants, green algae, and bacteria. In this review, we highlight the similarities and differences in auxin biosynthesis among these organisms. Tryptophan-dependent routes to IAA are found in land plants, green algae and bacteria. Recent sequencing efforts show that the indole-3-pyruvic acid pathway, one of the primary biosynthetic pathways in land plants, is also found in the green algae. These similarities raise questions about the origin of auxin biosynthesis. Future studies comparing auxin biosynthesis across kingdoms will shed light on its origin and role outside of the plant lineage.

Biosynthesis and Regulation of Salicylic Acid and N-Hydroxypipecolic Acid in Plant Immunity

Salicylic acid (SA) has long been known to be essential for basal defense and systemic acquired resistance (SAR). N-Hydroxypipecolic acid (NHP), a recently discovered plant metabolite, also plays a key role in SAR and to a lesser extent in basal resistance. Following pathogen infection, levels of both compounds are dramatically increased. Analysis of SA- or SAR-deficient mutants has uncovered how SA and NHP are biosynthesized. The completion of the SA and NHP biosynthetic pathways in Arabidopsis allowed better understanding of how they are regulated. In this review, we discuss recent progress on SA and NHP biosynthesis and their regulation in plant immunity.

Auxin Metabolism Controls Developmental Decisions in Land Plants

Unlike animals, whose body plans are set during embryo development, plants maintain the ability to initiate new organs throughout their life cycle. Auxin is a key regulator of almost all aspects of plant development, including morphogenesis and adaptive responses. Cellular auxin concentrations influence whether a cell will divide, grow, or differentiate, thereby contributing to organ formation, growth, and ultimately plant shape. Auxin gradients are established and maintained by a tightly regulated interplay between metabolism, signalling, and transport. Auxin is synthesised, stored, and inactivated by a multitude of parallel pathways that are all tightly regulated. Here we summarise the remarkable progress that has been achieved in identifying some key components of these pathways and the genetic complexity underlying their precise regulation.

Functional characterization of Gh_A08G1120 (GH3.5) gene reveal their significant role in enhancing drought and salt stress tolerance in cotton

BACKGROUND

Auxins play an important role in plant growth and development; the auxins responsive gene; auxin/indole-3-acetic acid (Aux/IAA), small auxin-up RNAs (SAUR) and Gretchen Hagen3 (GH3) control their mechanisms. The GH3 genes function in homeostasis by the catalytic activities in auxin conjugation and bounding free indole-3-acetic acid (IAA) to amino acids.

RESULTS

In our study, we identified the GH3 genes in three cotton species; Gossypium hirsutum, Gossypium arboreum and Gossypium raimondii, analyzed their chromosomal distribution, phylogenetic relationships, cis-regulatory element function and performed virus induced gene silencing of the novel Gh_A08G1120 (GH3.5) gene. The phylogenetic tree showed four clusters of genes with clade 1, 3 and 4 having mainly members of the GH3 of the cotton species while clade 2 was mainly members belonging to Arabidopsis. There were no paralogous genes, and few orthologous genes were observed between Gossypium and other species. All the GO terms were detected, but only 14 genes were found to have described GO terms in upland cotton, more biological functions were detected, as compared to the other functions. The GH3.17 subfamily harbored the highest number of the cis-regulatory elements, most having promoters towards dehydration-responsiveness. The RNA expression analysis revealed that 10 and 8 genes in drought and salinity stress conditions respectively were upregulated in G. hirsutum. All the genes that were upregulated in plants under salt stress conditions were also upregulated in drought stress; moreover, Gh_A08G1120 (GH3.5) exhibited a significant upregulation across the two stress factors. Functional characterization of Gh_A08G1120 (GH3.5) through virus-induced gene silencing (VIGS) revealed that the VIGS plants ability to tolerate drought and salt stresses was significantly reduced compared to the wild types. The chlorophyll content, relative leaf water content (RLWC), and superoxide dismutase (SOD) concentration level were reduced significantly while malondialdehyde concentration and ion leakage as a measure of cell membrane stability (CMS) increased in VIGS plants under drought and salt stress conditions.

CONCLUSION

This study revealed the significance of the GH3 genes in enabling the plant's adaptation to drought and salt stress conditions as evidenced by the VIGS results and RT-qPCR analysis.

Evolutionary Analysis of GH3 Genes in Six Oryza Species/Subspecies and Their Expression under Salinity Stress in Oryza sativa ssp. japonica

Glycoside Hydrolase 3 (GH3), a member of the Auxin-responsive gene family, is involved in plant growth, the plant developmental process, and various stress responses. The GH3 gene family has been well-studied in Arabidopsis thaliana and Zea mays. However, the evolution of the GH3 gene family in Oryza species remains unknown and the function of the GH3 gene family in Oryza sativa is not well-documented. Here, a systematic analysis was performed in six Oryza species/subspecies, including four wild rice species and two cultivated rice subspecies. A total of 13, 13, 13, 13, 12, and 12 members were identified in O. sativa ssp. japonica, O. sativa ssp. indica, Oryza rufipogon, Oryza nivara, Oryza punctata, and Oryza glumaepatula, respectively. Gene duplication events, structural features, conserved motifs, a phylogenetic analysis, chromosome locations, and Ka/Ks ratios of this important family were found to be strictly conservative across these six Oryza species/subspecies, suggesting that the expansion of the GH3 gene family in Oryza species might be attributed to duplication events, and this expansion could occur in the common ancestor of Oryza species, even in common ancestor of rice tribe (Oryzeae) (23.07~31.01 Mya). The RNA-seq results of different tissues displayed that OsGH3 genes had significantly different expression profiles. Remarkably, the qRT-PCR result after NaCl treatment indicated that the majority of OsGH3 genes play important roles in salinity stress, especially OsGH3-2 and OsGH3-8. This study provides important insights into the evolution of the GH3 gene family in Oryza species and will assist with further investigation of OsGH3 genes’ functions under salinity stress.

Comparative Genomic and Transcriptomic Analysis Suggests the Evolutionary Dynamic of GH3 Genes in Gramineae Crops

Glycoside hydrolase 3 (GH3) gene family belongs to auxin-responsive gene families and is tightly linked with hormone homeostasis and signaling pathways. However, our knowledge about the evolutionary dynamic of GH3 genes in Gramineae crops is limited. In this study, a comparative genomic and transcriptomic analysis was conducted to study evolutionary patterns and the driving selective forces of GH3 gene family in six representative Gramineae crops, namely, Setaria italica (Si), Zea mays (Zm), Sorghum bicolor (Sb), Hordeum vulgare (Hv), Brachypodium distachyon (Bd), and Oryza sativa ssp. japonica (Os). A total of 17, 13, 11, 9, 8, and 11 GH3 proteins (GH3s) were identified in Si, Zm, Sb, Hv, Bd, and Os, respectively. Phylogenetic, conserved motif, and gene structural analyses could divide all GH3s into two groups (I and II), and all GH3s consisted of seven orthogroups (Ors) on the basis of Or identification result. We further found that genes in the same Or showed similar sequence and structural features, whereas genes in the same groups exhibited intrinsic differences in exon numbers and intron lengths. These results revealed GH3 genes in the same groups have been differentiated. Obvious differences in total numbers of GH3 genes, Ors, and duplication events among these six tested Gramineae crops reflected lineage-specific expansions and homologous gene loss/gain of GH3 gene family during the evolutionary process. In addition, selective force and expression analyses indicated that all GH3 genes were constrained by strong purifying selection, and GH3 genes in conserved Ors showed higher expression levels than that in unconserved Ors. The current study highlighted different evolutionary patterns of GH3 genes in Gramineae crops resulted from different evolutionary rates and duplication events and provided a vital insight into the functional divergence of GH3 genes.