Expression profile of PIN, AUX/LAX and PGP auxin transporter gene families in Sorghum bicolor under phytohormone and abiotic stress

Transcriptome analysis reveals ozone treatment maintains ascorbic acid content in fresh-cut kiwifruit by regulating phytohormone signalling pathways

Ascorbic acid (AsA) is an indicator of the nutritional value of freshly cut kiwifruit during storage at 4℃, and its degradation can be inhibited after ozone treatment (1 mg/L, 10 min). The aim of this study was to elucidate the regulatory mechanism affecting AsA metabolism in fresh-cut kiwifruit after ozone treatment. In this study, ozone treatment not only prevented the decrease in AsA/dehydroascorbic acid and delayed the accumulation of total soluble solids/titratable acidity, but also altered phytohormone levels differently. Transcriptomic profiling combined with cis-acting element and correlation analysis were performed to reveal that abscisic acid and salicylic acid synergistically delay AsA degradation under ozone-treatment conditions. Actinidia03760, encoding ascorbate peroxidase, could be specifically recognized by the bZIP transcription factor and is considered a key candidate gene for further research. Collectively, ozone treatment is a promising method for preserving AsA content and improving the nutrition of fresh-cut kiwifruit.

A transcriptome-wide identification of ATP-binding cassette (ABC) transporters revealed participation of ABCB subfamily in abiotic stress management of Glycyrrhiza glabra L

Transcriptome-wide survey divulged a total of 181 ABC transporters in G. glabra which were phylogenetically classified into six subfamilies. Protein-Protein interactions revealed nine putative GgABCBs (-B6, -B14, -B15, -B25, -B26, -B31, -B40, -B42 &-B44) corresponding to five AtABCs orthologs (-B1, -B4, -B11, -B19, &-B21). Significant transcript accumulation of ABCB6 (31.8 folds), -B14 (147.5 folds), -B15 (17 folds), -B25 (19.7 folds), -B26 (18.31 folds), -B31 (61.89 folds), -B40 (1273 folds) and -B42 (51 folds) was observed under the influence of auxin. Auxin transport-specific inhibitor, N-1-naphthylphthalamic acid, showed its effectiveness only at higher (10 µM) concentration where it down regulated the expression of ABCBs, PINs (PIN FORMED) and TWD1 (TWISTED DWARF 1) genes in shoot tissues, while their expression was seen to enhance in the root tissues. Further, qRT-PCR analysis under various growth conditions (in-vitro, field and growth chamber), and subjected to abiotic stresses revealed differential expression implicating role of ABCBs in stress management. Seven of the nine genes were shown to be involved in the stress physiology of the plant. GgABCB6, 15, 25 and ABCB31 were induced in multiple stresses, while GgABCB26, 40 & 42 were exclusively triggered under drought stress. No study pertaining to the ABC transporters from G. glabra is available till date. The present investigation will give an insight to auxin transportation which has been found to be associated with plant growth architecture; the knowledge will help to understand the association between auxin transportation and plant responses under the influence of various conditions.

Genome Identification and Expression Profiling of the PIN-Formed Gene Family in Phoebe bournei under Abiotic Stresses

PIN-formed (PIN) proteins-specific transcription factors that are widely distributed in plants-play a pivotal role in regulating polar auxin transport, thus influencing plant growth, development, and abiotic stress responses. Although the identification and functional validation of PIN genes have been extensively explored in various plant species, their understanding in woody plants-particularly the endangered species Phoebe bournei (Hemsl.) Yang-remains limited. P. bournei is an economically significant tree species that is endemic to southern China. For this study, we employed bioinformatics approaches to screen and identify 13 members of the PIN gene family in P. bournei. Through a phylogenetic analysis, we classified these genes into five sub-families: A, B, C, D, and E. Furthermore, we conducted a comprehensive analysis of the physicochemical properties, three-dimensional structures, conserved motifs, and gene structures of the PbPIN proteins. Our results demonstrate that all PbPIN genes consist of exons and introns, albeit with variations in their number and length, highlighting the conservation and evolutionary changes in PbPIN genes. The results of our collinearity analysis indicate that the expansion of the PbPIN gene family primarily occurred through segmental duplication. Additionally, by predicting cis-acting elements in their promoters, we inferred the potential involvement of PbPIN genes in plant hormone and abiotic stress responses. To investigate their expression patterns, we conducted a comprehensive expression profiling of PbPIN genes in different tissues. Notably, we observed differential expression levels of PbPINs across the various tissues. Moreover, we examined the expression profiles of five representative PbPIN genes under abiotic stress conditions, including heat, cold, salt, and drought stress. These experiments preliminarily verified their responsiveness and functional roles in mediating responses to abiotic stress. In summary, this study systematically analyzes the expression patterns of PIN genes and their response to abiotic stresses in P. bournei using whole-genome data. Our findings provide novel insights and valuable information for stress tolerance regulation in P. bournei. Moreover, the study offers significant contributions towards unraveling the functional characteristics of the PIN gene family.

Auxins and grass shoot architecture: how the most important hormone makes the most important plants

Cereals are a group of grasses cultivated by humans for their grain. It is from these cereal grains that the majority of all calories consumed by humans are derived. The production of these grains is the result of the development of a series of hierarchical reproductive structures that form the distinct shoot architecture of the grasses. Being spatiotemporally complex, the coordination of grass shoot development is tightly controlled by a network of genes and signals, including the key phytohormone auxin. Hormonal manipulation has therefore been identified as a promising potential approach to increasing cereal crop yields and therefore ultimately global food security. Recent work translating the substantial body of auxin research from model plants into cereal crop species is revealing the contribution of auxin biosynthesis, transport, and signalling to the development of grass shoot architecture. This review discusses this still-maturing knowledge base and examines the possibility that changes in auxin biology could have been a causative agent in the evolution of differences in shoot architecture between key grass species, or could underpin the future selective breeding of cereal crops.

Overexpression of OsPIN9 Impairs Chilling Tolerance via Disturbing ROS Homeostasis in Rice

The auxin efflux transporter PIN-FORMED (PIN) family is one of the major protein families that facilitates polar auxin transport in plants. Here, we report that overexpression of OsPIN9 leads to altered plant architecture and chilling tolerance in rice. The expression profile analysis indicated that OsPIN9 was gradually suppressed by chilling stress. The shoot height and adventitious root number of OsPIN9-overexpressing (OE) plants were significantly reduced at the seedling stage. The roots of OE plants were more tolerant to N-1-naphthylphthalamic acid (NPA) treatment than WT plants, indicating the disturbance of auxin homeostasis in OE lines. The chilling tolerance assay showed that the survival rate of OE plants was markedly lower than that of wild-type (WT) plants. Consistently, more dead cells, increased electrolyte leakage, and increased malondialdehyde (MDA) content were observed in OE plants compared to those in WT plants under chilling conditions. Notably, OE plants accumulated more hydrogen peroxide (H2O2) and less superoxide anion radicals (O2-) than WT plants under chilling conditions. In contrast, catalase (CAT) and superoxide dismutase (SOD) activities in OE lines decreased significantly compared to those in WT plants at the early chilling stage, implying that the impaired chilling tolerance of transgenic plants is probably attributed to the sharp induction of H2O2 and the delayed induction of antioxidant enzyme activities at this stage. In addition, several OsRboh genes, which play a crucial role in ROS production under abiotic stress, showed an obvious increase after chilling stress in OE plants compared to that in WT plants, which probably at least in part contributes to the production of ROS under chilling stress in OE plants. Together, our results reveal that OsPIN9 plays a vital role in regulating plant architecture and, more importantly, is involved in regulating rice chilling tolerance by influencing auxin and ROS homeostasis.

Integrating stay-green and PIN-FORMED genes: PIN-FORMED genes as potential targets for designing climate-resilient cereal ideotypes

Plant architecture modification (e.g. short-stature crops) is one of the key outcomes of modern crop breeding for high-yielding crop varieties. In cereals, delayed senescence, or stay-green, is an important trait that enables post-anthesis drought stress adaptation. Stay-green crops can prolong photosynthetic capacity during grain-filling period under post-anthesis drought stress, which is essential to ensure grain yield is not impacted under drought stress conditions. Although various stay-green quantitative trait loci have been identified in cereals, the underlying molecular mechanisms regulating stay-green remain elusive. Recent advances in various gene-editing technologies have provided avenues to fast-track crop improvement, such as the breeding of climate-resilient crops in the face of climate change. We present in this viewpoint the focus on using sorghum as the model cereal crop, to study PIN-FORMED (PIN) auxin efflux carriers as means to modulate plant architecture, and the potential to employ it as an adaptive strategy to address the environmental challenges posed by climate uncertainties.

Regulation of Reactive Oxygen Species during Salt Stress in Plants and Their Crosstalk with Other Signaling Molecules-Current Perspectives and Future Directions

Salt stress is a severe type of environmental stress. It adversely affects agricultural production worldwide. The overproduction of reactive oxygen species (ROS) is the most frequent phenomenon during salt stress. ROS are extremely reactive and, in high amounts, noxious, leading to destructive processes and causing cellular damage. However, at lower concentrations, ROS function as secondary messengers, playing a critical role as signaling molecules, ensuring regulation of growth and adjustment to multifactorial stresses. Plants contain several enzymatic and non-enzymatic antioxidants that can detoxify ROS. The production of ROS and their scavenging are important aspects of the plant's normal response to adverse conditions. Recently, this field has attracted immense attention from plant scientists; however, ROS-induced signaling pathways during salt stress remain largely unknown. In this review, we will discuss the critical role of different antioxidants in salt stress tolerance. We also summarize the recent advances on the detrimental effects of ROS, on the antioxidant machinery scavenging ROS under salt stress, and on the crosstalk between ROS and other various signaling molecules, including nitric oxide, hydrogen sulfide, calcium, and phytohormones. Moreover, the utilization of "-omic" approaches to improve the ROS-regulating antioxidant system during the adaptation process to salt stress is also described.

Genetic modification of PIN genes induces causal mechanisms of stay-green drought adaptation phenotype

The stay-green trait is recognized as a key drought adaptation mechanism in cereals worldwide. Stay-green sorghum plants exhibit delayed senescence of leaves and stems, leading to prolonged growth, a reduced risk of lodging, and higher grain yield under end-of-season drought stress. More than 45 quantitative trait loci (QTL) associated with stay-green have been identified, including two major QTL (Stg1 and Stg2). However, the contributing genes that regulate functional stay-green are not known. Here we show that the PIN FORMED family of auxin efflux carrier genes induce some of the causal mechanisms driving the stay-green phenotype in sorghum, with SbPIN4 and SbPIN2 located in Stg1 and Stg2, respectively. We found that nine of 11 sorghum PIN genes aligned with known stay-green QTL. In transgenic studies, we demonstrated that PIN genes located within the Stg1 (SbPIN4), Stg2 (SbPIN2), and Stg3b (SbPIN1) QTL regions acted pleiotropically to modulate canopy development, root architecture, and panicle growth in sorghum, with SbPIN1, SbPIN2, and SbPIN4 differentially expressed in various organs relative to the non-stay-green control. The emergent consequence of such modifications in canopy and root architecture is a stay-green phenotype. Crop simulation modelling shows that the SbPIN2 phenotype can increase grain yield under drought.

Genome-wide identification and expression analysis of PIN gene family under phytohormone and abiotic stresses in Vitis Vinifera L

The auxin efflux transport proteins PIN-formed (PIN) has wide adaptability to hormone and abiotic stress, but the response mechanism of PINs in grape remains unclear. In this study, 12 members of VvPINs were identified and distributed on 8 chromosomes. The PIN genes of five species were divided into two subgroups, and the similarity of exons/introns and motifs of VvPIN genes were found in the same subgroup. Meanwhile, according to the examination of conserved motifs, the motif 3 included the conserved structure NPNTY. The promoter region of VvPIN gene family contained various cis-acting elements, which were related to light, abiotic stress, and hormones which are essential for growth and development. Additionally, VvPIN1, VvPIN9, and VvPIN11 proteins simultaneously interacted with the ARF, ABC, PINOID, GBF1, and VIT_08s0007g09010. The results of qRT-PCR revealed that the majority of the VvPINs were highly induced by NAA, GA3, ABA, MeJA, SA, NaCl, low-temperature (4 ℃), and PEG treatments, and the results were consistent with the prediction of the cis-acting elements. Moreover, the expression profile and quantitative real-time PCR (qRT-PCR) demonstrated that VvPIN genes were expressed in roots, stems, and leaves. The subcellular localization of VvPIN1 in Nicotiana benthamiana revealed that VvPIN1 was localized at the plasma membrane. Collectively, this study revealed that PIN genes could respond to various abiotic stresses, and provided a framework for regulating the expression of PIN genes to enhance the resistance of the grape.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01239-8.

Expression analysis of PIN family genes in Chinese hickory reveals their potential roles during grafting and salt stress

Grafting is an effective way to improve Chinese hickory while salt stress has caused great damage to the Chinese hickory industry. Grafting and salt stress have been regarded as the main abiotic stress types for Chinese hickory. However, how Chinese hickory responds to grafting and salt stress is less studied. Auxin has been proved to play an essential role in the stress response through its re-distribution regulation mediated by polar auxin transporters, including PIN-formed (PIN) proteins. In this study, the PIN gene family in Chinese hickory (CcPINs) was identified and structurally characterized for the first time. The expression profiles of the genes in response to grafting and salt stress were determined. A total of 11 CcPINs with the open reading frames (ORFs) of 1,026-1,983 bp were identified. Transient transformation in tobacco leaves demonstrated that CcPIN1a, CcPIN3, and CcPIN4 were localized in the plasma membrane. There were varying phylogenetic relationships between CcPINs and homologous genes in different species, but the closest relationships were with those in Carya illinoinensis and Juglans regia. Conserved N- and C-terminal transmembrane regions as well as sites controlling the functions of CcPINs were detected in CcPINs. Five types of cis-acting elements, including hormone- and stress-responsive elements, were detected on the promoters of CcPINs. CcPINs exhibited different expression profiles in different tissues, indicating their varied roles during growth and development. The 11 CcPINs responded differently to grafting and salt stress treatment. CcPIN1a might be involved in the regulation of the grafting process, while CcPIN1a and CcPIN8a were related to the regulation of salt stress in Chinese hickory. Our results will lay the foundation for understanding the potential regulatory functions of CcPIN genes during grafting and under salt stress treatment in Chinese hickory.

Euryale Small Auxin Up RNA62 promotes cell elongation and seed size by altering the distribution of indole-3-acetic acid under the light

Euryale (Euryale ferox Salisb.) is an aquatic crop used as both food and drug in Asia, but its utilization is seriously limited due to low yield. Previously, we hypothesized that Euryale small auxin up RNAs (EuSAURs) regulate seed size, but the underlying biological functions and molecular mechanisms remain unclear. Here, we observed that the hybrid Euryale lines (HL) generate larger seeds with higher indole-3-acetic acid (IAA) concentrations than those in the North Gordon Euryale (WT). Histological analysis suggested that a larger ovary in HL is attributed to longer cells around. Overexpression of EuSAUR62 in rice (Oryza sativa L.) resulted in larger glumes and grains and increased the length of glume cells. Immunofluorescence and protein interaction assays revealed that EuSAUR62 modulates IAA accumulation around the rice ovary by interacting with the rice PIN-FORMED 9, an auxin efflux carrier protein. Euryale basic region/leucine zipper 55 (EubZIP55), which was highly expressed in HL, directly binds to the EuSAUR62 promoter and activated the expression of EuSAUR62. Constant light increased the expression of both EubZIP55 and EuSAUR62 with auxin-mediated hook curvature in HL seedlings. Overall, we proposed that EuSAUR62 is a molecular bridge between light and IAA and plays a crucial role in regulating the size of the Euryale seed.

Mutation of OsPIN1b by CRISPR/Cas9 Reveals a Role for Auxin Transport in Modulating Rice Architecture and Root Gravitropism

The distribution and content of auxin within plant tissues affect a variety of important growth and developmental processes. Polar auxin transport (PAT), mainly mediated by auxin influx and efflux transporters, plays a vital role in determining auxin maxima and gradients in plants. The auxin efflux carrier PIN-FORMED (PIN) family is one of the major protein families involved in PAT. Rice (Oryza sativa L.) genome possesses 12 OsPIN genes. However, the detailed functions of OsPIN genes involved in regulating the rice architecture and gravity response are less well understood. In the present study, OsPIN1b was disrupted by CRISPR/Cas9 technology, and its roles in modulating rice architecture and root gravitropism were investigated. Tissue-specific analysis showed that OsPIN1b was mainly expressed in roots, stems and sheaths at the seedling stage, and the transcript abundance was progressively decreased during the seedling stages. Expression of OsPIN1b could be quickly and greatly induced by NAA, indicating that OsPIN1b played a vital role in PAT. IAA homeostasis was disturbed in ospin1b mutants, as evidenced by the changed sensitivity of shoot and root to NAA and NPA treatment, respectively. Mutation of OsPIN1b resulted in pleiotropic phenotypes, including decreased growth of shoots and primary roots, reduced adventitious root number in rice seedlings, as well as shorter and narrower leaves, increased leaf angle, more tiller number and decreased plant height and panicle length at the late developmental stage. Moreover, ospin1b mutants displayed a curly root phenotype cultured with tap water regardless of lighting conditions, while nutrient solution culture could partially rescue the curly root phenotype in light and almost completely abolish this phenotype in darkness, indicating the involvement of the integration of light and nutrient signals in root gravitropism regulation. Additionally, amyloplast sedimentation was impaired in the peripheral tiers of the ospin1b root cap columella cell, while it was not the main contributor to the abnormal root gravitropism. These data suggest that OsPIN1b not only plays a vital role in regulating rice architecture but also functions in regulating root gravitropism by the integration of light and nutrient signals.

PIN3 from Liriodendron May Function in Inflorescence Development and Root Elongation

Auxin, the first discovered phytohormone, is important for the growth and development of plants through the establishment of homeostasis and asymmetry. Here, we cloned the auxin transporter gene PIN-FORMED3 (PIN3) from the valuable timber tree hybrid Liriodendron (Liriodendron chinense × Liriodendron tulipifera). The gene contained a complete open reading frame of 1917 bp that encoded 638 amino acids. Phylogenetic analysis indicated that LhPIN3 exhibited the highest sequence similarity to the PIN3 of Vitis vinifera. Quantitative real-time PCR analysis showed that LhPIN3 was broadly expressed across different tissues/organs of Liriodendron, with the highest expression level in the roots. Heterologous overexpression of LhPIN3 in Arabidopsis thaliana caused considerable phenotypic changes, such as the root length and number of flowers. Genetic complementation of Arabidopsis pin1 mutants by LhPIN3, driven by the cauliflower mosaic virus 35S promoter, fully restored the root length and number of flowers of the pin1 mutant. Overall, our findings reveal that LhPIN3 has similar capacities to regulate the root length and number of flowers of Arabidopsis with AtPIN1.

Transcriptome Analysis Reveals Key Pathways and Candidate Genes Controlling Seed Development and Size in Ricebean (Vigna umbellata)

Ricebean (Vigna umbellata) is a lesser known pulse with well-recognized potential. Recently, it has emerged as a legume with endowed nutritional potential because of high concentration of quality protein and other vital nutrients in its seeds. However, the genes and pathways involved in regulating seed development and size are not understood in this crop. In our study, we analyzed the transcriptome of two genotypes with contrasting grain size (IC426787: large seeded and IC552985: small seeded) at two different time points, namely, 5 and 10 days post-anthesis (DPA). The bold seeded genotype across the time points (B5_B10) revealed 6,928 differentially expressed genes (DEGs), whereas the small seeded genotype across the time point (S5_S10) contributed to 14,544 DEGs. We have also identified several candidate genes for seed development–related traits like seed size and 100-seed weight. On the basis of similarity search and domain analysis, some candidate genes (PHO1, cytokinin dehydrogenase, A-type cytokinin, and ARR response negative regulator) related to 100-seed weight and seed size showed downregulation in the small seeded genotype. The MapMan and KEGG analysis confirmed that auxin and cytokinin pathways varied in both the contrasting genotypes and can therefore be the regulators of the seed size and other seed development–related traits in ricebeans. A total of 51 genes encoding SCF^TIR1/AFB, Aux/IAA, ARFs, E3 ubiquitin transferase enzyme, and 26S proteasome showing distinct expression dynamics in bold and small genotypes were also identified. We have also validated randomly selected SSR markers in eight accessions of the Vigna species (V. umbellata: 6; Vigna radiata: 1; and Vigna mungo: 1). Cross-species transferability pattern of ricebean–derived SSR markers was higher in V. radiata (73.08%) than V. mungo (50%). To the best of our knowledge, this is the first transcriptomic study conducted in this crop to understand the molecular basis of any trait. It would provide us a comprehensive understanding of the complex transcriptome dynamics during the seed development and gene regulatory mechanism of the seed size determination in ricebeans.

Cryo-Treatment Enhances the Embryogenicity of Mature Somatic Embryos via the lncRNA-miRNA-mRNA Network in White Spruce

In conifers, somatic embryogenesis is uniquely initiated from immature embryos in a narrow time window, which is considerably hindered by the difficulty to induce embryogenic tissue (ET) from other tissues, including mature somatic embryos. In this study, the embryogenic ability of newly induced ET and DNA methylation levels was detected, and whole-transcriptome sequencing analyses were carried out. The results showed that ultra-low temperature treatment significantly enhanced ET induction from mature somatic embryos, with the induction rate from 0.4% to 15.5%, but the underlying mechanisms remain unclear. The newly induced ET showed higher capability in generating mature embryos than the original ET. DNA methylation levels fluctuated during the ET induction process. Here, WGCNA analysis revealed that OPT4, TIP1-1, Chi I, GASA5, GST, LAX3, WRKY7, MYBS3, LRR-RLK, PBL7, and WIN1 genes are involved in stress response and auxin signal transduction. Through co-expression analysis, lncRNAs MSTRG.505746.1, MSTRG.1070680.1, and MSTRG.33602.1 might bind to pre-novel_miR_339 to promote the expression of WRKY7 genes for stress response; LAX3 could be protected by lncRNAs MSTRG.1070680.1 and MSTRG.33602.1 via serving as sponges for novel_miR_495 to initiate auxin signal transduction; lncRNAs MSTRG.505746.1, MSTRG.1070680.1, and MSTRG.33602.1 might serve as sponges for novel_miR_527 to enhance the expression of Chi I for early somatic embryo development. This study provides new insight into the area of stress-enhanced early somatic embryogenesis in conifers, which is also attributable to practical applications.

Transcriptome Analysis of Lolium temulentum Exposed to a Combination of Drought and Heat Stress

Drought and heat are two major stresses predicted to increase in the future due to climate change. Plants exposed to multiple stressors elicit unique responses from those observed under individual stresses. A comparative transcriptome analysis of Lolium temulentum exposed to drought plus heat and non-stressed control plants revealed 20,221 unique up-regulated and 17,034 unique down-regulated differentially regulated transcripts. Gene ontology analysis revealed a strong emphasis on transcriptional regulation, protein folding, cell cycle/parts, organelles, binding, transport, signaling, oxidoreductase, and antioxidant activity. Differentially expressed genes (DEGs) encoding for transcriptional control proteins such as basic leucine zipper, APETALA2/Ethylene Responsive Factor, NAC, and WRKY transcription factors, and Zinc Finger (CCCH type and others) proteins were more often up-regulated, while DEGs encoding Basic Helix-Loop-Helix, MYB and GATA transcription factors, and C2H2 type Zinc Finger proteins were more often down-regulated. The DEGs encoding heat shock transcription factors were only up-regulated. Of the hormones, auxin-related DEGs were the most prevalent, encoding for auxin response factors, binding proteins, and efflux/influx carriers. Gibberellin-, cytokinin- and ABA-related DEGs were also prevalent, with fewer DEGs related to jasmonates and brassinosteroids. Knowledge of genes/pathways that grasses use to respond to the combination of heat/drought will be useful in developing multi-stress resistant grasses.

Drought and High Temperature Stress in Sorghum: Physiological, Genetic, and Molecular Insights and Breeding Approaches

Sorghum is one of the staple crops for millions of people in Sub-Saharan Africa (SSA) and South Asia (SA). The future climate in these sorghum production regions is likely to have unexpected short or long episodes of drought and/or high temperature (HT), which can cause significant yield losses. Therefore, to achieve food and nutritional security, drought and HT stress tolerance ability in sorghum must be genetically improved. Drought tolerance mechanism, stay green, and grain yield under stress has been widely studied. However, novel traits associated with drought (restricted transpiration and root architecture) need to be explored and utilized in breeding. In sorghum, knowledge on the traits associated with HT tolerance is limited. Heat shock transcription factors, dehydrins, and genes associated with hormones such as auxin, ethylene, and abscisic acid and compatible solutes are involved in drought stress modulation. In contrast, our understanding of HT tolerance at the omic level is limited and needs attention. Breeding programs have exploited limited traits with narrow genetic and genomic resources to develop drought or heat tolerant lines. Reproductive stages of sorghum are relatively more sensitive to stress compared to vegetative stages. Therefore, breeding should incorporate appropriate pre-flowering and post-flowering tolerance in a broad genetic base population and in heterotic hybrid breeding pipelines. Currently, more than 240 QTLs are reported for drought tolerance-associated traits in sorghum prospecting discovery of trait markers. Identifying traits and better understanding of physiological and genetic mechanisms and quantification of genetic variability for these traits may enhance HT tolerance. Drought and HT tolerance can be improved by better understanding mechanisms associated with tolerance and screening large germplasm collections to identify tolerant lines and incorporation of those traits into elite breeding lines. Systems approaches help in identifying the best donors of tolerance to be incorporated in the SSA and SA sorghum breeding programs. Integrated breeding with use of high-throughput precision phenomics and genomics can deliver a range of drought and HT tolerant genotypes that can improve yield and resilience of sorghum under drought and HT stresses.

Primary root and root hair development regulation by OsAUX4 and its participation in the phosphate starvation response

Among the five members of AUX1/LAX genes coding for auxin carriers in rice, only OsAUX1 and OsAUX3 have been reported. To understand the function of the other AUX1/LAX genes, two independent alleles of osaux4 mutants, osaux4-1 and osaux4-2, were constructed using the CRISPR/Cas9 editing system. Homozygous osaux4-1 or osaux4-2 exhibited shorter primary root (PR) and longer root hair (RH) compared to the wild-type Dongjin (WT/DJ), and lost response to indoleacetic acid (IAA) treatment. OsAUX4 is intensively expressed in roots and localized on the plasma membrane, suggesting that OsAUX4 might function in the regulation of root development. The decreased meristem cell division activity and the downregulated expression of cell cycle genes in root apices of osaux4 mutants supported the hypothesis that OsAUX4 positively regulates PR elongation. OsAUX4 is expressed in RH, and osaux4 mutants showing longer RH compared to WT/DJ implies that OsAUX4 negatively regulates RH development. Furthermore, osaux4 mutants are insensitive to Pi starvation (-Pi) and OsAUX4 effects on the -Pi response is associated with altered expression levels of Pi starvation-regulated genes, and auxin distribution/contents. This study revealed that OsAUX4 not only regulates PR and RH development but also plays a regulatory role in crosstalk between auxin and -Pi signaling.

Genome-Wide Identification and Characterization of PIN-FORMED (PIN) Gene Family Reveals Role in Developmental and Various Stress Conditions in Triticum aestivum L

PIN-FORMED (PIN) genes play a crucial role in regulating polar auxin distribution in diverse developmental processes, including tropic responses, embryogenesis, tissue differentiation, and organogenesis. However, the role of PIN-mediated auxin transport in various plant species is poorly understood. Currently, no information is available about this gene family in wheat (Triticum aestivum L.). In the present investigation, we identified the PIN gene family in wheat to understand the evolution of PIN-mediated auxin transport and its role in various developmental processes and under different biotic and abiotic stress conditions. In this study, we performed genome-wide analysis of the PIN gene family in common wheat and identified 44 TaPIN genes through a homology search, further characterizing them to understand their structure, function, and distribution across various tissues. Phylogenetic analyses led to the classification of TaPIN genes into seven different groups, providing evidence of an evolutionary relationship with Arabidopsis thaliana and Oryza sativa. A gene exon/intron structure analysis showed a distinct evolutionary path and predicted the possible gene duplication events. Further, the physical and biochemical properties, conserved motifs, chromosomal, subcellular localization, transmembrane domains, and three-dimensional (3D) structure were also examined using various computational approaches. Cis-elements analysis of TaPIN genes showed that TaPIN promoters consist of phytohormone, plant growth and development, and stress-related cis-elements. In addition, expression profile analysis also revealed that the expression patterns of the TaPIN genes were different in different tissues and developmental stages. Several members of the TaPIN family were induced during biotic and abiotic stress. Moreover, the expression patterns of TaPIN genes were verified by qRT-PCR. The qRT-PCR results also show a similar expression with slight variation. Therefore, the outcome of this study provides basic genomic information on the expression of the TaPIN gene family and will pave the way for dissecting the precise role of TaPINs in plant developmental processes and different stress conditions.

Characterization of auxin transporter AUX, PIN and PILS gene families in pineapple and evaluation of expression profiles during reproductive development and under abiotic stresses

Polar auxin transport in plant is mediated by influx and efflux transporters, which are encoded by AUX/LAX, PIN and PILS genes, respectively. The auxin transporter gene families have been characterized in several species from monocots and eudicots. However, a genome-wide overview of auxin transporter gene families in pineapple is not yet available. In this study, we identified a total of threeAcAUX genes, 12 AcPIN genes, and seven AcPILS genes in the pineapple genome, which were variably located on 15 chromosomes. The exon-intron structure of these genes and properties of deduced proteins were relatively conserved within the same family. Most protein motifs were widespread in the AUX, PIN or PILS proteins, whereas a few motifs were absent in only one or two proteins. Analysis of the expression profiles of these genes elucidated that several genes exhibited either preferential or tissue-specific expression patterns in vegetative and/or reproductive tissues. AcAUX2 was specifically expressed in the early developmental ovules, while AcPIN1b and AcPILS2 were strongly expressed in stamens and ovules. AcPIN9b, AcPILS1, AcPILS6a, 6b and 6c were abundantly expressed in stamens. Furthermore, qRT-PCR results showed that several genes in these families were responsive to various abiotic stresses. Comparative analysis indicated that the genes with close evolutionary relationships among pineapple, rice and Arabidopsis exhibited similar expression patterns. Overexpression of the AcAUX1 in Arabidopsis rescued the phenotype in aux1-T, and resulted in increased lateral roots in WT. These results will provide new insights into auxin transporter genes of pineapple and facilitate our understanding of their roles in pineapple growth and development.

Identification, pyramid and candidate genes of QTLs for associated traits based on a dense erect panicle rice CSSL-Z749 and five SSSLs, three DSSLs and one TSSL

BACKGROUND

Seed-set density is an important agronomic trait in rice. However, its genetic mechanism is complex. Chromosome segment substitution lines (CSSLs) are ideal materials for studying complex traits.

RESULTS

A rice CSSL, Z749, with a dense and erect panicle phenotype, was identified among progeny of the recipient parent Nipponbare and the donor parent Xihui 18. Z749 carried seven substitution segments (average length 2.12 Mb). Compared with Nipponbare, Z749 showed significant increases in the numbers of primary (NPB) and secondary branches (NSB), number of spikelets (SPP) and grains per panicle (GPP), seed-set density (SSD), and decrease in panicle length (PL). A secondary F₂ population derived from a cross between Nipponbare and Z749 was used to map quantitative trait loci (QTLs) for associated traits. Fifteen QTLs distributed on chromosomes 5, 7, 8, and 10 were detected. The QTL qPL7 might be an allele of OsFAD8 and the remaining 14 QTLs (e.g., qSSD5 and qSSD10 etc.) might be novel. Fourteen QTLs were verified using five single-segment substitution lines (SSSLs). The seed-set density of Z749 was controlled predominantly by one major QTL (qSSD10) and two minor QTLs (qSSD5 and qSSD8). The QTLs qSSD10, qSSD5, and qSSD8 were fine-mapped to intervals of 1.05, 1.46, and 1.53 Mb on chromosomes 10, 5, and 8, respectively. Analysis of QTL additive effects indicated that qSSD5, qSSD8, and qSSD10 from Xihui18 increased seed-set density of Z749 by 14.10, 11.38, and 5.11 spikelets per 10 cm panicle, respectively. Analysis of QTL epistatic effects revealed that pyramiding of qSSD5 and qSSD8, qSSD5 and qSSD10, qSSD8 and qSSD10, and qSSD5, qSSD8 and qSSD10 produced novel genotypes with increased seed-set density.

CONCLUSIONS

Inheritance of seed-set density in Z749 was controlled predominantly by one major QTL (qSSD10) and two minor QTLs (qSSD5 and qSSD8). Then, they were fine-mapped to intervals of 1.05, 1.46, and 1.53 Mb on chromosomes 10, 5, 8, respectively. Two MAPK genes (OsMPK9 and OsMPK17) and one gene (candidate gene 6) involved in auxin metabolism might be candidate genes for qSSD5, and OsSAUR32 might be the candidate gene for qSSD8. Pyramiding of qSSD5, qSSD8, and qSSD10 enhanced seed-set density.

Reference genes for quantitative real-time PCR normalization of Cenostigma pyramidale roots under salt stress and mycorrhizal association

Cenostigma pyramidale is a native legume of the Brazilian semiarid region which performs symbiotic association with arbuscular mycorrhizal fungi (AMF), being an excellent model for studying genes associated with tolerance against abiotic and biotic stresses. In RT-qPCR approach, the use of reference genes is mandatory to avoid incorrect interpretation of the relative expression. This study evaluated the stability of ten candidate reference genes (CRGs) from C. pyramidale root tissues under salt stress (three collection times) and associated with AMF (three different times of salinity). The de novo transcriptome was obtained via RNA-Seq sequencing. Three algorithms were used to calculate the stability of CRGs under different conditions: (i) global (Salt, Salt+AMF, AMF and Control, and collection times), (ii) only non-inoculated plants, and (iii) AMF (only inoculated plants). HAG2, SAC1, aRP3 were the most stable CRGs for global and AMF assays, whereas HAG2, SAC1, RHS1 were the best for salt stress assay. This CRGs were used to validate the relative expression of two up-regulated transcripts in Salt2h (RAP2-3 and PIN8). Our study provides the first set of reference genes for C. pyramidale under salinity and AMF, supporting future researches on gene expression with this species.

Comprehensive Analysis and Expression Profiling of PIN, AUX/LAX, and ABCB Auxin Transporter Gene Families in Solanum tuberosum under Phytohormone Stimuli and Abiotic Stresses

Simple Summary

In this study, we provide comprehensive information on auxin transporter gene families in potato, including basic parameters, chromosomal distribution, phylogeny, co-expression network analysis, gene structure, tissue-specific expression patterns, subcellular localization, transcription analysis under exogenous hormone stimuli and abiotic stresses, and cis-regulatory element prediction. The responsiveness of auxin transporter family genes to auxin and polar auxin transport inhibitors implied their possible roles in auxin homoeostasis and redistribution. Additionally, the differential expression levels of auxin transporter family genes in response to abscisic acid and abiotic stresses suggested their specific adaptive mechanisms on tolerance to various environmental stimuli. Promoter cis-regulatory element description analyses indicated that a number of cis-regulatory elements within the promoters of auxin transporter genes in potato were targeted by relevant transcription factors to respond to diverse stresses. We are confident that our results provide a foundation for a better understanding of auxin transporters in potato, as we have demonstrated the biological significance of this family of genes in hormone signaling and adaption to environmental stresses.

Abstract

Auxin is the only plant hormone that exhibits transport polarity mediated by three families: auxin resistant (AUX) 1/like AUX1 (LAX) influx carriers, pin-formed (PIN) efflux carriers, and ATP-binding cassette B (ABCB) influx/efflux carriers. Extensive studies about the biological functions of auxin transporter genes have been reported in model plants. Information regarding these genes in potato remains scarce. Here, we conducted a comprehensive analysis of auxin transporter gene families in potato to examine genomic distributions, phylogeny, co-expression analysis, gene structure and subcellular localization, and expression profiling using bioinformatics tools and qRT-PCR analysis. From these analyses, 5 StLAXs, 10 StPINs, and 22 StABCBs were identified in the potato genome and distributed in 10 of 18 gene modules correlating to the development of various tissues. Transient expression experiments indicated that three representative auxin transporters showed plasma membrane localizations. The responsiveness to auxin and auxin transport inhibitors implied their possible roles in mediating intercellular auxin homoeostasis and redistribution. The differential expression under abscisic acid and abiotic stresses indicated their specific adaptive mechanisms regulating tolerance to environmental stimuli. A large number of auxin-responsive and stress-related cis-elements within their promoters could account for their responsiveness to diverse stresses. Our study aimed to understand the biological significance of potato auxin transporters in hormone signaling and tolerance to environmental stresses.

Genome-Wide Identification of Barley ABC Genes and Their Expression in Response to Abiotic Stress Treatment

Adenosine triphosphate-binding cassette transporters (ABC transporters) participate in various plant growth and abiotic stress responses. In the present study, 131 ABC genes in barley were systematically identified using bioinformatics. Based on the classification method of the family in rice, these members were classified into eight subfamilies (ABCA-ABCG, ABCI). The conserved domain, amino acid composition, physicochemical properties, chromosome distribution, and tissue expression of these genes were predicted and analyzed. The results showed that the characteristic motifs of the barley ABC genes were highly conserved and there were great diversities in the homology of the transmembrane domain, the number of exons, amino acid length, and the molecular weight, whereas the span of the isoelectric point was small. Tissue expression profile analysis suggested that ABC genes possess non-tissue specificity. Ultimately, 15 differentially expressed genes exhibited diverse expression responses to stress treatments including drought, cadmium, and salt stress, indicating that the ABCB and ABCG subfamilies function in the response to abiotic stress in barley.

The WUSCHEL-related homeobox transcription factor OsWOX4 controls the primary root elongation by activating OsAUX1 in rice

Primary root is the basic component of root system and plays a key role in early seedling growth and survival in rice. However, the molecular mechanism of primary root elongation still needs to be well understood. Here, we showed that OsWOX4, a WUSCHEL-related homeobox (WOX) transcription factor, was involved in the primary root elongation in rice. Silencing of OsWOX4 by RNA interference (RNAi) greatly increased the primary root length, whereas its overexpression reduced primary root elongation significantly. Moreover, the size of meristem zone and epidermal cell length of mature zone in RNAi root tips were drastically enhanced, while they were reduced markedly in overexpression lines, in comparison with that of wild type. Further analysis showed that the accumulation of free IAA was slightly increased in RNAi roots, but drastically reduced in plants overexpressing OsWOX4. The expression of genes responsible for auxin biosynthesis and transport was also changed in OsWOX4 transgenic lines. Transient transcriptional activation and electrophoretic mobility shift assays showed that OsWOX4 directly regulated the transcription of OsAUX1 through binding to its promoter region. Collectively, our results indicated that OsWOX4 played a crucial role in the primary root elongation by regulating auxin transport, suggesting its importance in rice root system architecture.

Genome-Wide Analysis of the PIN Auxin Efflux Carrier Gene Family in Coffee

Coffee is one of the most popular beverages around the world, which is mainly produced from the allopolyploid Coffea arabica. The genomes of C. arabica and its two ancestors C. canephora and C. eugenioides have been released due to the development of next generation sequencing. However, few studies on C. arabica are related to the PIN-FORMED (PIN) auxin efflux transporter despite its importance in auxin-mediated plant growth and development. In the present study, we conducted a genome-wide analysis of the PIN gene family in the three coffee species. Totals of 17, 9 and 10 of the PIN members were characterized in C. Arabica, C. canephora and C. eugenioides, respectively. Phylogenetic analysis revealed gene loss of PIN1 and PIN2 homologs in C. arabica, as well as gene duplication of PIN5 homologs during the fractionation process after tetraploidy. Furthermore, we conducted expression analysis of PIN genes in C. arabica by in silico and qRT-PCR. The results revealed the existence of gene expression dominance in allopolyploid coffee and illustrated several PIN candidates in regulating auxin transport and homeostasis under leaf rust fungus inoculation and the tissue-specific expression pattern of C. arabica. Together, this study provides the basis and guideline for future functional characterization of the PIN gene family.

Auxin-mediated responses under salt stress: from developmental regulation to biotechnological applications

As sessile organisms, plants are exposed to multiple abiotic stresses commonly found in nature. To survive, plants have developed complex responses that involve genetic, epigenetic, cellular, and morphological modifications. Among different environmental cues, salt stress has emerged as a critical problem contributing to yield losses and marked reductions in crop production. Moreover, as the climate changes, it is expected that salt stress will have a significant impact on crop production in the agroindustry. On a mechanistic level, salt stress is known to be regulated by the crosstalk of many signaling molecules such as phytohormones, with auxin having been described as a key mediator of the process. Auxin plays an important role in plant developmental responses and stress, modulating a complex balance of biosynthesis, transport, and signaling that among other things, finely tune physiological changes in plant architecture and Na+ accumulation. In this review, we describe current knowledge on auxin's role in modulating the salt stress response. We also discuss recent and potential biotechnological approaches to tackling salt stress.

Characterization of the Auxin Efflux Transporter PIN Proteins in Pear

PIN-FORMED (PIN) encodes a key auxin polar transport family that plays a crucial role in the outward transport of auxin and several growth and development processes, including dwarfing trees. We identified a dwarfing pear rootstock 'OHF51' (Pyrus communis), which limits the growth vigor of the 'Xueqing' (Pyrus bretschneideri × Pyrus pyrifolia) scion, and isolated 14 putative PbPINs from the pear Pyrus bretschneideri. The phylogenic relationships, structure, promoter regions, and expression patterns were analyzed. PbPINs were classified into two main groups based on the protein domain structure and categorized into three major groups using the neighbor-joining algorithm. Promoter analysis demonstrated that PbPINs might be closely related to plant growth and development. Through quantitative real-time PCR (qRT-PCR) analysis, we found that the expression patterns of 14 PbPINs varied upon exposure to different organs in dwarfing and vigorous stocks, 'OHF51' and 'QN101' (Pyrus betulifolia), indicating that they might play varying roles in different tissues and participated in the regulation of growth vigor. These results provide fundamental insights into the characteristics and evolution of the PINs family, as well as the possible relationship between dwarfing ability and auxin polar transport.

Comparative Proteomics Profiling Illuminates the Fruitlet Abscission Mechanism of Sweet Cherry as Induced by Embryo Abortion

Sweet cherry (Prunus avium L.) is a delicious nutrient-rich fruit widely cultivated in countries such as China, America, Chile, and Italy. However, the yield often drops severely due to the frequently-abnormal fruitlet abscission, and few studies on the metabolism during its ripening process at the proteomic level have been executed so far. To get a better understanding regarding the sweet cherry abscission mechanism, proteomic analysis between the abscising carpopodium and non-abscising carpopodium of sweet cherry was accomplished using a newly developed Liquid chromatography-mass spectrometry/mass spectrometry with Tandem Mass Tag (TMT-LC-MS/MS) methodology. The embryo viability experiments showed that the vigor of the abscission embryos was significantly lower than that of retention embryo. The activity of cell wall degrading enzymes in abscising carpopodium was significantly higher than that in non-abscising carpopodium. The anatomy results suggested that cells in the abscission zone were small and separated. In total, 6280 proteins were identified, among which 5681 were quantified. It has been observed that differentially accumulated proteins (DAPs) influenced several biological functions and various subcellular localizations. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that plenty of metabolic pathways were notably enriched, particularly those involved in phytohormone biosynthesis, cell wall metabolism, and cytoskeletal metabolism, including 1-aminocyclopropane-1-carboxylate oxidase proteins which promote ethylene synthesis, and proteins promoting cell wall degradation, such as endoglucanases, pectinase, and polygalacturonase. Differential expression of proteins concerning phytohormone biosynthesis might activate the shedding regulation signals. Up-regulation of several cell wall degradation-related proteins possibly regulated the shedding of plant organs. Variations of the phytohormone biosynthesis and cell wall degradation-related proteins were explored during the abscission process. Furthermore, changes in cytoskeleton-associated proteins might contribute to the abscission of carpopodium. The current work represented the first study using comparative proteomics between abscising carpopodium and non-abscising carpopodium. These results indicated that embryo abortion might lead to phytohormone synthesis disorder, which effected signal transduction pathways, and hereby controlled genes involved in cell wall degradation and then caused the abscission of fruitlet. Overall, our data may give an intrinsic explanation of the variations in metabolism during the abscission of carpopodium.

Expression Profile of PIN-Formed Auxin Efflux Carrier Genes during IBA-Induced In Vitro Adventitious Rooting in Olea europaea L

Exogenous auxins supplementation plays a central role in the formation of adventitious roots (AR) for several plant species. However, the molecular mechanisms underlying the process of adventitious rooting are still not completely understood and many plants with economic value, including several olive cultivars, exhibit a recalcitrant behavior towards cutting propagation, which limits its availability in plant nurseries. PIN-formed proteins are auxin efflux transporters that have been widely characterized in several plant species due to their involvement in many developmental processes including root formation. The present study profiled the expression of the OePIN1a-c, OePIN2b, OePIN3a-c, OePIN5a-c, OePIN6, and OePIN8 gene members during indole-3-butyric acid (IBA)-induced in vitro adventitious rooting using the olive cultivar ‘Galega vulgar’. Gene expression analysis by quantitative real time PCR (RT-qPCR) showed drastic downregulation of most transcripts, just a few hours after explant inoculation, in both nontreated and IBA-treated microcuttings, albeit gene downregulation was less pronounced in IBA-treated stems. In contrast, OePIN2b showed a distinct expression pattern being upregulated in both conditions, and OePIN5b was highly upregulated in IBA-induced stems. All transcripts, except OePIN8, showed different expression profiles between nontreated and IBA-treated explants throughout the rooting experiment. Additionally, high levels of reactive oxygen species (ROS) were observed soon after explant preparation, decreasing a few hours after inoculation. Altogether, the results suggest that wounding-related ROS production, associated with explant preparation for rooting, may have an impact on auxin transport and distribution via changes in OePIN gene expression. Moreover, the application of exogenous auxin may modulate auxin homeostasis through regulation of those genes, leading to auxin redistribution throughout the stem-base tissue, which may ultimately play an important role in AR formation.

Molecular Characterization of Auxin Efflux Carrier- ABCB1 in hexaploid wheat

Auxin is an important phytohormone that regulates response, differentiation, and development of plant cell, tissue, and organs. Along with its local production, long-distance transport coordinated by the efflux/influx membrane transporters is instrumental in plant development and architecture. In the present study, we cloned and characterized a wheat (Triticum aestivum) auxin efflux carrier ABCB1. The TaABCB1 was physically localized to the proximal 15% of the short arm of wheat homoeologous group 7 chromosomes. Size of the Chinese spring (CS) homoeologs genomic copies ranged from 5.3–6.2 kb with the 7A copy being the largest due to novel insertions in its third intron. The three homoeologous copies share 95–97% sequence similarity at the nucleotide, 98–99% amino acid, and overall Q-score of 0.98 at 3-D structure level. Though detected in all analyzed tissues, TaABCB1 predominantly expressed in the meristematic tissues likely due to the presence of meristem-specific activation regulatory element identified in the promoter region. RNAi plants of TaABCB1 gene resulted in reduced plant height and increased seed width. Promoter analysis revealed several responsive elements detected in the promoter region including that for different hormones as auxin, gibberellic acid, jasmonic acid and abscisic acid, light, and circadian regulated elements.

Drought Stress Effects and Olive Tree Acclimation under a Changing Climate

Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor.

The auxin influx carrier, OsAUX3, regulates rice root development and responses to aluminium stress

In rice, there are five members of the auxin carrier AUXIN1/LIKE AUX1 family; however, the biological functions of the other four members besides OsAUX1 remain unknown. Here, by using CRISPR/Cas9, we constructed two independent OsAUX3 knock-down lines, osaux3-1 and osaux3-2, in wild-type rice, Hwayoung (WT/HY) and Dongjin (WT/DJ). osaux3-1 and osaux3-2 have shorter primary roots (PRs), decreased lateral root (LR) density, and longer root hairs (RHs) compared with their WT. OsAUX3 expression in PRs, LRs, and RHs further supports that OsAUX3 plays a critical role in the regulation of root development. OsAUX3 locates at the plasma membrane and functions as an auxin influx carrier affecting acropetal auxin transport. OsAUX3 is up-regulated in the root apex under aluminium (Al) stress, and osaux3-2 is insensitive to Al treatments. Furthermore, 1-naphthylacetic acid accented the sensitivity of WT/DJ and osaux3-2 to respond to Al stress. Auxin concentrations, Al contents, and Al-induced reactive oxygen species-mediated damage in osaux3-2 under Al stress are lower than in WT, indicating that OsAUX3 is involved in Al-induced inhibition of root growth. This study uncovers a novel pathway alleviating Al-induced oxidative damage by inhibition of acropetal auxin transport and provides a new option for engineering Al-tolerant rice species.

High-throughput quantitative analysis of phytohormones in sorghum leaf and root tissue by ultra-performance liquid chromatography-mass spectrometry

Plant development, growth, and adaptation to stress are regulated by phytohormones, which can influence physiology even at low concentrations. Phytohormones are chemically grouped according to both structure and function as auxins, cytokinins, abscisic acid, jasmonates, salicylates, gibberellins, and brassinosteroids, among others. This chemical diversity and requirement for highly sensitive detection in complex matrices create unique challenges for comprehensive phytohormone analysis. Here, we present a robust and efficient quantitative UPLC-MS/MS assay for 17 phytohormones, including jasmonates, salicylates, abscisic acid, gibberellins, cytokinins, and auxins. Using this assay, 12 phytohormones were detected and quantified in sorghum plant tissue without the need for solid phase extraction (SPE) or liquid-liquid extraction. Variation of phytohormone profiles was explored in both root and leaf tissues between three genotypes, harvested at two different developmental time points. The results highlight the importance of tissue type, sampling time, and genetic factors when designing experiments that involve phytohormone analysis of sorghum. This research lays the groundwork for future studies, which can combine phytohormone profiling with other datasets such as transcriptome, soil microbiome, genome, and metabolome data, to provide important functional information about adaptation to stress and other environmental variables.

Up-regulation of lipid biosynthesis increases the oil content in leaves of Sorghum bicolor

Synthesis and accumulation of the storage lipid triacylglycerol in vegetative plant tissues has emerged as a promising strategy to meet the world's future need for vegetable oil. Sorghum (Sorghum bicolor) is a particularly attractive target crop given its high biomass, drought resistance and C₄ photosynthesis. While oilseed-like triacylglycerol levels have been engineered in the C₃ model plant tobacco, progress in C₄ monocot crops has been lagging behind. In this study, we report the accumulation of triacylglycerol in sorghum leaf tissues to levels between 3 and 8.4% on a dry weight basis depending on leaf and plant developmental stage. This was achieved by the combined overexpression of genes encoding the Zea mays WRI1 transcription factor, Umbelopsis ramanniana UrDGAT2a acyltransferase and Sesamum indicum Oleosin-L oil body protein. Increased oil content was visible as lipid droplets, primarily in the leaf mesophyll cells. A comparison between a constitutive and mesophyll-specific promoter driving WRI1 expression revealed distinct changes in the overall leaf lipidome as well as transitory starch and soluble sugar levels. Metabolome profiling uncovered changes in the abundance of various amino acids and dicarboxylic acids. The results presented here are a first step forward towards the development of sorghum as a dedicated biomass oil crop and provide a basis for further combinatorial metabolic engineering.

Rice Calcineurin B-Like Protein-Interacting Protein Kinase 31 (OsCIPK31) Is Involved in the Development of Panicle Apical Spikelets

Panicle apical abortion (PAA) causes severe yield losses in rice production, but details about its development and molecular basis remain elusive. Herein, a PAA mutant, paa1019, was identified among the progeny of an elite indica maintainer rice line Yixiang 1B (YXB) mutagenized population obtained using ethyl methyl sulfonate. The abortion rate of spikelets in paa1019 was observed up to 60%. Genetic mapping combined with Mutmap analysis revealed that LOC_Os03g20380 harbored a single-bp substitution (C to T) that altered its transcript length. This gene encodes calcineurin B-like protein-interacting protein kinase 31 (OsCIPK31) localized into the cytoplasm, and is preferentially expressed in transport tissues of rice. Complementation of paa1019 by transferring the open reading frame of LOC_Os03g20380 from YXB reversed the mutant phenotype, and conversely, gene editing by knocking out of OsCIPK31 in YXB results in PAA phenotype. Our results support that OsCIPK31 plays an important role in panicle development. We found that dysregulation is caused by the disruption of OsCIPK31 function due to excessive accumulation of ROS, which ultimately leads to cell death in rice panicle. OsCIPK31 and MAPK pathway might have a synergistic effect to lead ROS accumulation in response to stresses. Meanwhile the PAA distribution is related to IAA hormone accumulation in the panicle. Our study provides an understanding of the role of OsCIPK31 in panicle development by responding to various stresses and phytohormones.

Novel perspectives on the molecular crosstalk mechanisms of serotonin and melatonin in plants

Current review focuses on the significant role of serotonin and melatonin in various molecular crosstalk mechanisms in plants. In this context phytohormones (like auxin, gibberellins, ethylene or abscisic acid), plant growth regulators, and associated biomolecules like reactive oxygen species, nitric oxide, brassinosteroids and hydrogen sulphide have been discussed in a wider context. Long distance signaling responses of serotonin in association with auxin, jasmonic acid, salicylic acid and ABA have been critically reviewed. Auxin-serotonin crosstalk in relation to PIN protein functioning and root growth regulation appears to be a major advancement in the context of phytoserotonin signaling in plants. Auxin and serotonin share structural similarities which bring possibilities of auxin receptors being surrogated for serotonin transport in plants. The modulation of root apex architecture is highly regulative in terms of serotonin-jasmonic acid crosstalk. Reactive oxygen species (ROS) appears to be a primary mediator of serotonin mediated root growth response. Serotonin induced signaling therefore involve ROS, auxin, JA and ethylene action. Although there exists handful of critical reviews on the role of phytomelatonin in plants, recent advancements on its regulatory role in modulating plant hormones, ROS scavenging enzymes, ROS/RNS and glutathione levels need attention. Melatonin signaling associated with nitrogen metabolism and nitrosative stress are recent developments in plants. Interesting relationship between nitric oxide and melatonin has been established in relation with biotic and abiotic stress tolerance in plants. Developments in hydrogen sulphide-melatonin signaling in plants are still at its nascent stage but exhibits promising scopes for future.

The PIN-FORMED Auxin Efflux Carriers in Plants

Auxin plays crucial roles in multiple developmental processes, such as embryogenesis, organogenesis, cell determination and division, as well as tropic responses. These processes are finely coordinated by the auxin, which requires the polar distribution of auxin within tissues and cells. The intercellular directionality of auxin flow is closely related to the asymmetric subcellular location of PIN-FORMED (PIN) auxin efflux transporters. All PIN proteins have a conserved structure with a central hydrophilic loop domain, which harbors several phosphosites targeted by a set of protein kinases. The activities of PIN proteins are finely regulated by diverse endogenous and exogenous stimuli at multiple layers-including transcriptional and epigenetic levels, post-transcriptional modifications, subcellular trafficking, as well as PINs' recycling and turnover-to facilitate the developmental processes in an auxin gradient-dependent manner. Here, the recent advances in the structure, evolution, regulation and functions of PIN proteins in plants will be discussed. The information provided by this review will shed new light on the asymmetric auxin-distribution-dependent development processes mediated by PIN transporters in plants.

Genome-wide identification and expression analysis of the CaLAX and CaPIN gene families in pepper (Capsicum annuum L.) under various abiotic stresses and hormone treatments

Auxin plays key roles in regulating plant growth and development as well as in response to environmental stresses. The intercellular transport of auxin is mediated by the following four gene families: ATP-binding cassette family B (ABCB), auxin resistant1/like aux1 (AUX/LAX), PIN-formed (PIN), and PIN-like (PILS). Here, the latest assembled pepper (Capsicum annuum L.) genome was used to characterise and analyse the CaLAX and CaPIN gene families. Genome-wide investigations into these families, including chromosomal distributions, phytogenic relationships, and intron/exon structures, were performed. In total, 4 CaLAX and 10 CaPIN genes were mapped to 10 chromosomes. Most of these genes exhibited varied tissue-specific expression patterns assessed by quantitative real-time PCR. The expression profiles of the CaLAX and CaPIN genes under various abiotic stresses (salt, drought, and cold), exogenous phytohormones (IAA, 6-BA, ABA, SA, and MeJA), and polar auxin transport inhibitor treatments were evaluated. Most CaLAX and CaPIN genes were altered by abiotic stress at the transcriptional level in both shoots and roots, and many CaLAX and CaPIN genes were regulated by exogenous phytohormones. Our study helps to identify candidate auxin transporter genes and to further analyse their biological functions in pepper development and in its adaptation to environmental stresses.

A comprehensive phylogeny of auxin homeostasis genes involved in adventitious root formation in carnation stem cuttings

Understanding the functional basis of auxin homeostasis requires knowledge about auxin biosynthesis, auxin transport and auxin catabolism genes, which is not always directly available despite the recent whole-genome sequencing of many plant species. Through sequence homology searches and phylogenetic analyses on a selection of 11 plant species with high-quality genome annotation, we identified the putative gene homologs involved in auxin biosynthesis, auxin catabolism and auxin transport pathways in carnation (Dianthus caryophyllus L.). To deepen our knowledge of the regulatory events underlying auxin-mediated adventitious root formation in carnation stem cuttings, we used RNA-sequencing data to confirm the expression profiles of some auxin homeostasis genes during the rooting of two carnation cultivars with different rooting behaviors. We also confirmed the presence of several auxin-related metabolites in the stem cutting tissues. Our findings offer a comprehensive overview of auxin homeostasis genes in carnation and provide a solid foundation for further experiments investigating the role of auxin homeostasis in the regulation of adventitious root formation in carnation.

Auxin enhances grafting success in Carya cathayensis (Chinese hickory)

MAIN CONCLUSION

Application of auxin to root stock and scion increases the success rate of grafting in Chinese hickory. The nuts of the Chinese hickory (Carya cathayensis) tree are considered both delicious and healthy. The popularity and high demand result is that the hickory nuts are of very high economical value for horticulture. This is particularly true for the Zhejiang province in eastern China where this tree is widely cultivated. However, there are several difficulties surrounding the hickory cultivation, such as for example long vegetative growth, tall trees, labour-intensive nut picking, and slow variety improvements. These complications form a great bottleneck in the expansion of the hickory industry. The development of an efficient grafting procedure could surpass at least some of these problems. In this study, we demonstrate that application of the auxin indole-3-acetic acid promotes the grafting process in hickory, whereas application of the auxin transport inhibitor 1-N-naphthylphthalamic acid inhibits the grafting process. Furthermore, we have identified hickory genes in the PIN, ABCB, and AUX/LAX-families known to encode influx and efflux carriers in the polar transport of auxin. We show that increased expression of several of these genes, such as CcPIN1b and CcLAX3, is correlating with successful grafting.

Perturbation of Auxin Homeostasis and Signaling by PINOID Overexpression Induces Stress Responses in Arabidopsis

Under normal and stress conditions plant growth require a complex interplay between phytohormones and reactive oxygen species (ROS). However, details of the nature of this crosstalk remain elusive. Here, we demonstrate that PINOID (PID), a serine threonine kinase of the AGC kinase family, perturbs auxin homeostasis, which in turn modulates rosette growth and induces stress responses in Arabidopsis plants. Arabidopsis mutants and transgenic plants with altered PID expression were used to study the effect on auxin levels and stress-related responses. In the leaves of plants with ectopic PID expression an accumulation of auxin, oxidative burst and disruption of hormonal balance was apparent. Furthermore, PID overexpression led to the accumulation of antioxidant metabolites, while pid knockout mutants showed only moderate changes in stress-related metabolites. These physiological changes in the plants overexpressing PID modulated their response toward external drought and osmotic stress treatments when compared to the wild type. Based on the morphological, transcriptome, and metabolite results, we propose that perturbations in the auxin hormone levels caused by PID overexpression, along with other hormones and ROS downstream, cause antioxidant accumulation and modify growth and stress responses in Arabidopsis. Our data provide further proof for a strong correlation between auxin and stress biology.

The PIN gene family in cotton (Gossypium hirsutum): genome-wide identification and gene expression analyses during root development and abiotic stress responses

Background

Cell elongation and expansion are significant contributors to plant growth and morphogenesis, and are often regulated by environmental cues and endogenous hormones. Auxin is one of the most important phytohormones involved in the regulation of plant growth and development and plays key roles in plant cell expansion and elongation. Cotton fiber cells are a model system for studying cell elongation due to their large size. Cotton is also the world’s most utilized crop for the production of natural fibers for textile and garment industries, and targeted expression of the IAA biosynthetic gene iaaM increased cotton fiber initiation. Polar auxin transport, mediated by PIN and AUX/LAX proteins, plays a central role in the control of auxin distribution. However, very limited information about PIN-FORMED (PIN) efflux carriers in cotton is known.

Results

In this study, 17 PIN-FORMED (PIN) efflux carrier family members were identified in the Gossypium hirsutum (G. hirsutum) genome. We found that PIN1–3 and PIN2 genes originated from the At subgenome were highly expressed in roots. Additionally, evaluation of gene expression patterns indicated that PIN genes are differentially induced by various abiotic stresses. Furthermore, we found that the majority of cotton PIN genes contained auxin (AuxREs) and salicylic acid (SA) responsive elements in their promoter regions were significantly up-regulated by exogenous hormone treatment.

Conclusions

Our results provide a comprehensive analysis of the PIN gene family in G. hirsutum, including phylogenetic relationships, chromosomal locations, and gene expression and gene duplication analyses. This study sheds light on the precise roles of PIN genes in cotton root development and in adaption to stress responses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3901-5) contains supplementary material, which is available to authorized users.

Genome-wide identification and evolution of the PIN-FORMED (PIN) gene family in Glycine max

Soybean (Glycine max) is one of the most important crop plants. Wild and cultivated soybean varieties have significant differences worth further investigation, such as plant morphology, seed size, and seed coat development; these characters may be related to auxin biology. The PIN gene family encodes essential transport proteins in cell-to-cell auxin transport, but little research on soybean PIN genes (GmPIN genes) has been done, especially with respect to the evolution and differences between wild and cultivated soybean. In this study, we retrieved 23 GmPIN genes from the latest updated G. max genome database; six GmPIN protein sequences were changed compared with the previous database. Based on the Plant Genome Duplication Database, 18 GmPIN genes have been involved in segment duplication. Three pairs of GmPIN genes arose after the second soybean genome duplication, and six occurred after the first genome duplication. The duplicated GmPIN genes retained similar expression patterns. All the duplicated GmPIN genes experienced purifying selection (Ka/Ks < 1) to prevent accumulation of non-synonymous mutations and thus remained more similar. In addition, we also focused on the artificial selection of the soybean PIN genes. Five artificially selected GmPIN genes were identified by comparing the genome sequence of 17 wild and 14 cultivated soybean varieties. Our research provides useful and comprehensive basic information for understanding GmPIN genes.

Analysis of Nicotiana tabacum PIN genes identifies NtPIN4 as a key regulator of axillary bud growth

The plant-specific PIN-FORMED (PIN) auxin efflux proteins have been well characterized in many plant species, where they are crucial in the regulation of auxin transport in various aspects of plant development. However, little is known about the exact roles of the PIN genes during plant development in Nicotiana species. This study investigated the PIN genes in tobacco (Nicotiana tabacum) and in two ancestral species (Nicotiana sylvestris and Nicotiana tomentosiformis). Genome-wide analysis of the N. tabacum genome identified 20 genes of the PIN family. An in-depth phylogenetic analysis of the PIN genes of N. tabacum, N. sylvestris and N. tomentosiformis was conducted. NtPIN4 expression was strongly induced by the application of exogenous indole-3-acetic acid (IAA), but was downregulated by the application of ABA, a strigolactone analogue, and cytokinin, as well as by decapitation treatments, suggesting that the NtPIN4 expression level is likely positively regulated by auxin. Expression analysis indicated that NtPIN4 was highly expressed in tobacco stems and shoots, which was further validated through analysis of the activity of the NtPIN4 promoter. We used CRISPR-Cas9 technology to generate mutants for NtPIN4 and observed that both T0 and T1 plants had a significantly increased axillary bud growth phenotype, as compared with the wild-type plants. Therefore, NtPIN4 offers an opportunity for studying auxin-dependent branching processes.

Genome-wide identification and expression analysis of ClLAX, ClPIN and ClABCB genes families in Citrullus lanatus under various abiotic stresses and grafting

Background

Auxin plays an important role in regulating plant growth and development as well as in the response of plants to abiotic stresses. Auxin is transported by three kinds of major protein families, including the AUXIN RESISTANT 1/LIKE AUX1 (AUX⁄LAX) influx carriers, the PIN-FORMED (PIN) efflux carriers and the ATP binding cassette B/P-glycoprotein/Multidrug-resistance (ABCB/MDR/PGP) efflux/condition carriers. The biological function of several auxin transporter genes has been well characterized in Arabidopsis thaliana. However, their function in response to exogenous auxin and abiotic stresses in watermelon (Citrullus lanatus. L) remained unknown.

Results

Here, the latest updated watermelon genome was used to characterise the ClLAX, ClPIN and ClABCB family genes from watermelon. The genome-wide analysis of the ClLAX, ClPIN and ClABCB family genes, including chromosome localisation, gene structure, and phylogenic relationships, was carried out. Seven ClLAXs, 11 ClPINs and 15 ClABCBs were mapped on 10 watermelon chromosomes. The expression profiles of the ClLAX, ClPIN and ClABCB genes under exogenous indole-3-acetic acid and various abiotic stresses (salt, drought, and cold stresses) treatments were performed by quantitative real-time PCR (qRT-PCR). The transcriptional level of majority ClLAX, ClPIN and ClABCB genes were changed by abiotic stresses in both shoots and roots. We also analysed the expression levels of ClLAX, ClPIN and ClABCB genes in graft response.

Conclusion

Analysis of the expression patterns of ClLAX, ClPIN and ClABCB genes under salt, drought, cold treatment and grafting response helps us to understand the possible roles of auxin transporter genes in watermelon adaptation to environmental stresses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-017-0500-z) contains supplementary material, which is available to authorized users.

A Genome-Scale Analysis of the PIN Gene Family Reveals Its Functions in Cotton Fiber Development

The PIN-FORMED (PIN) protein, the most important polar auxin transporter, plays a critical role in the distribution of auxin and controls multiple biological processes. However, characterizations and functions of this gene family have not been identified in cotton. Here, we identified the PIN family in Gossypium hirsutum, Gossypium arboreum, and Gossypium raimondii. This gene family was divided into seven subgroups. A chromosomal distribution analysis showed that GhPIN genes were evenly distributed in eight chromosomes and that the whole genome and dispersed duplications were the main duplication events for GhPIN expansion. qRT-PCR analysis showed a tissue-specific expression pattern for GhPIN. Likely due to the cis-element variations in their promoters, transcripts of PIN6 and PIN8 genes from the At (tetraploid genome orginated from G. arboreum) subgenome and PIN1a from the Dt (tetraploid genome orginated from G. raimondii) subgenome in G. hirsutum was significantly increased compared to the transcripts in the diploids. The differential regulation of these PIN genes after the polyploidization may be conducive to fiber initiation and elongation. Exogenously applied auxin polar transport inhibitor significantly suppressed fiber growth, which is consistent with the essential function of these PIN genes for regulating cotton fiber development. Furthermore, the overexpression of GhPIN1a_Dt, GhPIN6_At, and GhPIN8_At in Arabidopsis promoted the density and length of trichomes in leaves.

Comprehensive Analysis of the Soybean (Glycine max) GmLAX Auxin Transporter Gene Family

The phytohormone auxin plays a critical role in regulation of plant growth and development as well as plant responses to abiotic stresses. This is mainly achieved through its uneven distribution in plant via a polar auxin transport process. Auxin transporters are major players in polar auxin transport. The AUXIN RESISTENT 1/LIKE AUX1 (AUX/LAX) auxin influx carriers belong to the amino acid permease family of proton-driven transporters and function in the uptake of indole-3-acetic acid (IAA). In this study, genome-wide comprehensive analysis of the soybean AUX/LAX (GmLAX) gene family, including phylogenic relationships, chromosome localization, and gene structure, was carried out. A total of 15 GmLAX genes, including seven duplicated gene pairs, were identified in the soybean genome. They were distributed on 10 chromosomes. Despite their higher percentage identities at the protein level, GmLAXs exhibited versatile tissue-specific expression patterns, indicating coordinated functioning during plant growth and development. Most GmLAXs were responsive to drought and dehydration stresses and auxin and abscisic acid (ABA) stimuli, in a tissue- and/or time point- sensitive mode. Several GmLAX members were involved in responding to salt stress. Sequence analysis revealed that promoters of GmLAXs contained different combinations of stress-related cis-regulatory elements. These studies suggest that the soybean GmLAXs were under control of a very complex regulatory network, responding to various internal and external signals. This study helps to identity candidate GmLAXs for further analysis of their roles in soybean development and adaption to adverse environments.