The lack of a systematic validation of reference genes: a serious pitfall undervalued in reverse transcription-polymerase chain reaction (RT-PCR) analysis in plants

Screening of reference genes for gene expression study in different tissues from the transcriptome data of the vector leafhopper Psammotettix striatus

Selecting appropriate reference genes is crucial for ensuring the accuracy and reliability of gene expression study using reverse transcription-quantitative PCR (RT-qPCR). To screen the optimal reference genes for analyzing gene expression in different tissues of the vector leafhopper Psammotettix striatus which causes extensive damage to a wide range of crops by vectoring multiple plant pathogenic microorganisms, the transcriptome data from Malpighian tubules (MTs) of P. striatus were mined. Twenty alternative candidate reference genes were initially selected for screening, among which seven genes with diverse Gene Ontology (GO) annotations were choosed as candidate reference genes, i.e., ribosomal protein L7A (RPL7A), ribosomal protein S28 (RPS28), ribosomal protein L22 (RPL22), ribosomal protein LP2 (RPLP2), H3 histone family 3A (H3F3A), elongation factor 1γ (EF-1γ), and elongation factor 1α (EF-1α). Gene expression levels in different tissues of P. striatus adults were examined using RT-qPCR, and their expression stability was analyzed using multiple reference gene screening software. This study revealed EF-1α as the most abundantly expressed gene, while RPL22 exhibited the lowest expression levels. EF-1α showed the most stable expression, whereas RPS28 showed the least stability. Various software tools confirmed EF-1α as the most stable single reference gene, and EF-1α and RPLP2 an optimal combination. This study provides a foundation for future investigation of the transmission of pathogenic microorganisms mediated by the vector leafhoppers, the function of the MTs, the biosynthesis of brochosomes, the coevolutionary processes and nutritional interactions of symbionts and host insects, and the gene expression study of other sap-sucking insects.

Reference genes for RT-qPCR analysis in Musa acuminata genotypes contrasting in resistance to Fusarium oxysporum f. sp. cubense subtropical race 4

Banana (Musa spp.) is the most widely consumed fruit globally. Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is a highly threatening disease to banana production. Resistance genes to Foc exist in wild Musa genotypes such as Musa acuminata subsp. burmannicoides var. Calcutta 4. Whilst real-time PCR (RT-qPCR) is appropriate for accurate analysis of gene expression in pathways involved in host defence responses, reference genes with stable expression under specific biotic stress conditions and host tissue types are necessary for normalization of sample variation. In this context, the stability in potential host reference genes ACT1, APT, EF1α, GAPDH, αTUB, RAN, UBIQ1, UBIQ2, βTUB1, βTUB3, L2 and ACTA1 was evaluated in total RNA samples from root tissues in Calcutta 4 (resistant) and Musa sp. cultivar Prata-anã (susceptible) extracted during interaction with Foc subtropical race 4 (STR4). Expression stability was calculated using the algorithms geNorm, NormFinder and BestKeeper. βTUB3 and L2 were identified as the most stable in Calcutta 4, with ACTA1 and GAPDH the most stable in Prata-anã. These reference genes for analysis of gene expression modulation in the Musa-Foc STR4 pathosystem are fundamental for advancing understanding of host defence responses to this important pathogen.

Selection of Reference Genes for Expression Normalization by RT-qPCR in Dracocephalum moldavica L

Dracocephalum moldavica is widely used as an ornamental, medicine, and perfume in industry. Real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) is widely and accurately utilized for gene expression evaluations. Selecting optimal reference genes is essential for normalizing RT-qPCR results. However, the identification of suitable reference genes in D. moldavica has not been documented. A total of 12 reference genes in D. moldavica were identified by PEG6000 (15%) treatment under hypertonia conditions in different tissues (roots, stem, leaves, flower, seeds and sepal) and during three stages of flower development, then used to validate the expression stability. There were four algorithms (delta Ct, geNorm, NormFinder, and BestKeeper) used to analyze the stability. Finally, the RefFinder program was employed to evaluate the candidate reference genes' stability. The results showed that ACTIN, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and EF1α (elongation factor-1α) were stable reference genes under the PEG6000 treatment. Heat shock protein 70 (HSP70) was the most stable gene across different flower development stages. ADP-ribosylation factor (ARF) was the most stable gene in different tissues and total samples. This study provides reliable gene expression studies for future research in D. moldavica.

Selection of stable reference genes for qPCR expression of Colletotrichum lindemuthianum, the bean anthracnose pathogen

Phaseolus vulgaris L., commonly known as the common bean, is a highly nutritious crop often called the "poor man's meat". However, it is susceptible to various diseases throughout the cropping season, with anthracnose caused by Colletotrichum lindemuthianum being a significant threat that leads to substantial losses. There is still a lack of understanding about the molecular basis of C. lindemuthianum pathogenicity. The first step in understanding this is to identify pathogenicity genes that express more during infection of common beans. A reverse transcription quantitative real-time PCR (qPCR) method can be used for virulence gene expression. However, this approach requires selecting appropriate reference genes to normalize relative gene expression data. Currently, there is no reference gene available for C. lindemuthianum. In this study, we selected eight candidate reference genes from the available genome of C. lindemuthianum to bridge the gap. These genes were ACT (Actin), β-tub (β-tubulin), EF (Elongation Factor), Cyt C (Cytochrome C), His H3 (Histone H3), CHS1 (Chitin synthetase), GAPDH (Glyceraldehyde-3-phosphate dehydrogenase) and abfA (Alpha-l-Arabinofuranosidase A). The primers for these candidate reference genes were able to amplify cDNA only from the pathogen, demonstrating their specificity. The qPCR efficiency of the primers ranged from 80% to 103%. We analyzed the stability of gene expression in C. lindemuthianum by exposing the mycelium to nine different stress conditions. We employed algorithms, such as GeNorm, NormFinder, BestKeeper, and RefFinder tools, to identify the most stable gene. The analysis using these tools revealed that EF, GAPDH, and β-tub most stable genes, while ACT and CHS1 showed relatively low expression stability. A large number of potential effector genes have been identified through bioinformatics analysis in C. lindemuthianum. The stable genes for qPCR (EF and GAPDH) discovered in this study will aid the scientific community in determining the relative expression of C. lindemuthianum effector genes.

Autophagy formation, microtubule disorientation, and alteration of ATG8 and tubulin gene expression under simulated microgravity in Arabidopsis thaliana

Autophagy plays an important role in plant growth and development, pathogen invasion and modulates plant response and adaptation to various abiotic stress stimuli. The biogenesis and trafficking of autophagosomes involve microtubules (MTs) as important actors in the autophagic process. However, initiation of autophagy in plants under microgravity has not been previously studied. Here we demonstrate how simulated microgravity induces autophagy development involving microtubular reorganization during period of autophagosome formation. It was shown that induction of autophagy with maximal autophagosome formation in root cells of Arabidopsis thaliana is observed after 6 days of clinostating, along with MT disorganization, which leads to visible changes in root morphology. Gradual decrease of autophagosome number was indicated on 9th and 12th days of the experiment as well as no significant re-orientation of MTs were identified. Respectively, analysis of α- and β-tubulins and ATG8 gene expression was carried out. In particular, the most pronounced increase of expression on both 6th and 9th days in response to simulated microgravity was detected for non-paralogous AtATG8b, AtATG8f, AtATG8i, and AtTUA2, AtTUA3 genes, as well as for the pair of β-tubulin duplicates, namely AtTUB2 and AtTUB3. Overall, the main autophagic response was observed after 6 and 9 days of exposure to simulated microgravity, followed by adaptive response after 12 days. These findings provide a key basis for further studies of cellular mechanisms of autophagy and involvement of cytoskeletal structures in autophagy biogenesis under microgravity, which would enable development of new approaches, aimed on enhancing plant adaptation to microgravity.

Selection and Validation of qRT-PCR Internal Reference Genes to Study Flower Color Formation in Camellia impressinervis

Real-time quantitative PCR (qRT-PCR) is a pivotal technique for gene expression analysis. To ensure reliable and accurate results, the internal reference genes must exhibit stable expression across varied experimental conditions. Currently, no internal reference genes for Camellia impressinervis have been established. This study aimed to identify stable internal reference genes from eight candidates derived from different developmental stages of C. impressinervis flowers. We employed geNorm, NormFinder, and BestKeeper to evaluate the expression stability of these candidates, which was followed by a comprehensive stability analysis. The results indicated that CiTUB, a tubulin gene, exhibited the most stable expression among the eight reference gene candidates in the petals. Subsequently, CiTUB was utilized as an internal reference for the qRT-PCR analysis of six genes implicated in the petal pigment synthesis pathway of C. impressinervis. The qRT-PCR results were corroborated by transcriptome sequencing data, affirming the stability and suitability of CiTUB as a reference gene. This study marks the first identification of stable internal reference genes within the entire genome of C. impressinervis, establishing a foundation for future gene expression and functional studies. Identifying such stable reference genes is crucial for advancing molecular research on C. impressinervis.

WOX2 functions redundantly with WOX1 and WOX4 to positively regulate seed germination in Arabidopsis

MAIN CONCLUSION

WOX family gene WOX2 is highly expressed during seed development, which functions redundantly with WOX1 and WOX4 to positively regulate seed germination. WOX (WUSCHEL-related homeobox) is a family of transcription factors in plants. They play essential roles in the regulation of plant growth and development, but their function in seed germination is not well understood. In this report, we show that WOX1, WOX2, and WOX4 are close homologues in Arabidopsis. WOX2 has a redundant function with WOX1 and WOX4, respectively, in seed germination. WOX2 is highly expressed during seed development, from the globular embryonic stage to mature dry seeds, and its expression is decreased after germination. Loss of function single mutant wox2, and double mutants wox1 wox2 and wox2 wox4-1 show decreased germination speed. WOX2 and WOX4 are essential for hypocotyl-radicle zone elongation during germination, potentially by promoting the expression of cell wall-related genes. We also found that WOX2 and WOX4 regulate germination through the gibberellin (GA) pathway. These results suggest that WOX2 and WOX4 integrate the GA pathway and downstream cell wall-related genes during germination.

The nuclear pore Y-complex functions as a platform for transcriptional regulation of FLOWERING LOCUS C in Arabidopsis

The nuclear pore complex (NPC) has multiple functions beyond the nucleo-cytoplasmic transport of large molecules. Subnuclear compartmentalization of chromatin is critical for gene expression in animals and yeast. However, the mechanism by which the NPC regulates gene expression is poorly understood in plants. Here we report that the Y-complex (Nup107-160 complex, a subcomplex of the NPC) self-maintains its nucleoporin homeostasis and modulates FLOWERING LOCUS C (FLC) transcription via changing histone modifications at this locus. We show that Y-complex nucleoporins are intimately associated with FLC chromatin through their interactions with histone H2A at the nuclear membrane. Fluorescence in situ hybridization assays revealed that Nup96, a Y-complex nucleoporin, enhances FLC positioning at the nuclear periphery. Nup96 interacted with HISTONE DEACETYLASE 6 (HDA6), a key repressor of FLC expression via histone modification, at the nuclear membrane to attenuate HDA6-catalyzed deposition at the FLC locus and change histone modifications. Moreover, we demonstrate that Y-complex nucleoporins interact with RNA polymerase II to increase its occupancy at the FLC locus, facilitating transcription. Collectively, our findings identify an attractive mechanism for the Y-complex in regulating FLC expression via tethering the locus at the nuclear periphery and altering its histone modification.

Selection of suitable reference genes for qPCR normalization in different developmental stages of Oenanthe javanica

Gene expression analysis is widely used to unravel molecular regulatory mechanisms and identify key genes in plants. Appropriate reference gene is an important prerequisite to ensure the accuracy and reliability of qPCR analysis results. Water dropwort is a plant of the Oenanthe genus in the Apiaceae family, which has high economic benefits. However, the underlying molecular regulatory mechanisms in the growth and development of water dropwort have not been fully understood and the appropriate reference genes in different developmental stages of water dropwort not yet reported. In this study, 10 candidate reference genes (ACTIN, PP2A, SAND, EF-1α, GAPDH, UBQ, MIP, TBP, RPS-18, eIF-4α) were identified and cloned from Oenanthe javanica. The qPCR primers of candidate reference genes were designed and verified. Four statistical algorithms, geNorm, NormFinder, BestKeeper and RefFinder were used to evaluate the expression stability of 10 candidate reference genes in different developmental stages of water dropwort. The results showed that TBP and UBQ were the most stable genes in different developmental stages of water dropwort, while GAPDH was the most unstable gene. The normalization of EXP1 genes at different developmental stages further confirmed the reliability of internal reference genes. The results of this study provide a theoretical basis for selecting appropriate internal reference genes in different developmental stages of water dropwort. This study also provides technical support and reliable basis for the expression analysis of key genes in different developmental stages of water dropwort.

Identification of Accurate Reference Genes for qRT-PCR Analysis of Gene Expression in Eremochloa ophiuroides under Multiple Stresses of Phosphorus Deficiency and/or Aluminum Toxicity

Centipedegrass (Eremochloa ophiuroides (Munro.) Hack.) is a species originating in China and is an excellent warm-season turfgrass. As a native species in southern China, it is naturally distributed in the phosphorus-deficient and aluminum-toxic acid soil areas. It is important to research the molecular mechanism of centipedegrass responses to phosphorus-deficiency and/or aluminum-toxicity stress. Quantitative Real-Time PCR (qRT-PCR) is a common method for gene expression analysis, and the accuracy of qRT-PCR results depends heavily on the stability of internal reference genes. However, there are still no reported stable and effective reference genes for qRT-PCR analysis of target genes under the acid-soil-related stresses in different organs of centipedegrass. For scientific rigor, the gene used as a reference for any plant species and/or any stress conditions should be first systematically screened and evaluated. This study is the first to provide a group of reliable reference genes to quantify the expression levels of functional genes of Eremochloa ophiuroides under multiple stresses of P deficiency and/or aluminum toxicity. In this study, centipedegrass seedlings of the acid-soil-resistant strain 'E041' and acid-soil-sensitive strain 'E089' were used for qRT-PCR analysis. A total of 11 candidate reference genes (ACT, TUB, GAPDH, TIP41, CACS, HNR, EP, EF1α, EIF4α, PP2A and actin) were detected by qRT-PCR technology, and the stability of candidate genes was evaluated with the combination of four internal stability analysis software programs. The candidate reference genes exhibited differential stability of expression in roots, stems and leaves under phosphorus-deficiency and/or aluminum-toxicity stress. On the whole, the results showed that GAPDH, TIP41 and HNR were the most stable in the total of samples. In addition, for different tissues under various stresses, the selected reference genes were also different. CACS and PP2A were identified as two stable reference genes in roots through all three stress treatments (phosphate deficiency, aluminum toxicity, and the multiple stress treatment of aluminum toxicity and phosphate deficiency). Moreover, CACS was also stable as a reference gene in roots under each treatment (phosphate deficiency, aluminum toxicity, or multiple stresses of aluminum toxicity and phosphate deficiency). In stems under all three stress treatments, GAPDH and EIF4α were the most stable reference genes; for leaves, PP2A and TIP41 showed the two highest rankings in all three stress treatments. Finally, qRT-PCR analysis of the expression patterns of the target gene ALMT1 was performed to verify the selected reference genes. The application of the reference genes identified as internal controls for qRT-PCR analysis will enable accurate analysis of the target gene expression levels and expression patterns in centipedegrass under acid-soil-related stresses.

Selection and Validation of Reference Genes for Reverse-Transcription Quantitative PCR Analysis in Sclerotium rolfsii

Reference genes are important for the accuracy of gene expression profiles using reverse-transcription quantitative PCR (RT-qPCR). However, there are no available reference genes reported for Sclerotium rolfsii; it actually has a pretty diverse and wide host range. In this study, seven candidate reference genes (UBC, β-TUB, 28S, 18S, PGK, EF1α and GAPDH) were validated for their expression stability in S. rolfsii under conditions of different developmental stages, populations, fungicide treatments, photoperiods and pHs. Four algorithm programs (geNorm, Normfinder, Bestkeeper and ΔCt) were used to evaluate the gene expression stability, and RefFinder was used to integrate the ranking results of four programs. Two reference genes were recommended by RefFinder for RT-qPCR normalization in S. rolfsii. The suitable reference genes were GAPDH and UBC across developmental stages, PGK and UBC across populations, GAPDH and PGK across fungicide treatments, EF1α and PGK across photoperiods, β-TUB and EF1α across pHs and PGK and GAPDH across all samples. Four target genes (atrB, PacC, WC1 and CAT) were selected for the validation of the suitability of selected reference genes. However, using one or two reference genes in combination to normalize the expression of target genes showed no significant difference in S. rolfsii. In short, this study provided reliable reference genes for studying the expression and function of genes in S. rolfsii.

Evaluation and validation of reference genes for RT-qPCR gene expression in Naegleria gruberi

Naegleria gruberi is a free-living amoeboflagellate commonly found in freshwater and in soils around the world. It is a non-pathogenic relative of Naegleria fowleri, which is the etiologic agent of Primary Amoebic Meningoencephalitis (PAM). PAM occurs world-wide and it is considered a rare disease, but its fatality rate is high (96%) mainly because of delay in initiation of treatment due to misdiagnosis and lack of a specific treatment. The analysis of gene expression by quantitative real-time PCR in N. gruberi could be a highly efficient means to understand the pathogenicity of N. fowleri and also to find drug targets. Accurate RT-qPCR analysis requires correct normalization of gene expression data using reference genes (RG), whose expression should be constant under different experimental conditions. In this study, six genes, representing the most frequently used housekeeping genes, were selected for evaluation as reference genes in N. gruberi. The expression and stability of these genes was evaluated employing four algorithms (geNorm, NormFinder, BestKeeper and RefFinder). This work shows significant variations of the stability of RGs depending on the algorithms employed and on the experimental conditions (i.e. logarithmic, stationary, heat-shock and oxidative stress). The geNorm, NormFinder and RefFinder analysis of all the experimental conditions in combination revealed that ACT and G6PD were the most stable RGs. While BestKeeper analysis showed that 18S and TBP were the most stable RGs. Moreover, normalization of HSP90 gene expression with the most stable RGs resulted in an upregulation whereas when the normalization was done with the unstable RGs, the gene expression was not reliable. Hence, the implications of this study are relevant to gene expression studies in N. gruberi.

Identification and evaluation of suitable reference genes for RT-qPCR analyses in Trichoderma atroviride under varying light conditions

BACKGROUND

Trichoderma atroviride is a competitive soil-borne mycoparasitic fungus with extensive applications as a biocontrol agent in plant protection. Despite its importance and application potential, reference genes for RT-qPCR analysis in T. atroviride have not been evaluated. Light exerts profound effects on physiology, such as growth, conidiation, secondary metabolism, and stress response in T. atroviride, as well as in other fungi. In this study, we aimed to address this gap by identifying stable reference genes for RT-qPCR experiments in T. atroviride under different light conditions, thereby enhancing accurate and reliable gene expression analysis in this model mycoparasite. We measured and compared candidate reference genes using commonly applied statistical algorithms.

RESULTS

Under cyclic light-dark cultivation conditions, tbp and rho were identified as the most stably expressed genes, while act1, fis1, btl, and sar1 were found to be the least stable. Similar stability rankings were obtained for cultures grown under complete darkness, with tef1 and vma1 emerging as the most stable genes and act1, rho, fis1, and btl as the least stable genes. Combining the data from both cultivation conditions, gapdh and vma1 were identified as the most stable reference genes, while sar1 and fis1 were the least stable. The selection of different reference genes had a significant impact on the calculation of relative gene expression, as demonstrated by the expression patterns of target genes pks4 and lox1.

CONCLUSION

The data emphasize the importance of validating reference genes for different cultivation conditions in fungi to ensure accurate interpretation of gene expression data.

Selection and validation of reliable reference genes for quantitative real-time PCR in Barnyard millet (Echinochloa spp.) under varied abiotic stress conditions

Quantitative real-time polymerase chain reaction (RT-qPCR) using a stable reference gene is widely used for gene expression research. Barnyard millet (Echinochloa spp.) is an ancient crop in Asia and Africa that is widely cultivated for food and fodder. It thrives well under drought, salinity, cold, and heat environmental conditions, besides adapting to any soil type. To date, there are no gene expression studies performed to identify the potential candidate gene responsible for stress response in barnyard millet, due to lack of reference gene. Here, 10 candidate reference genes, Actin (ACT), α-tubulin (α-TUB), β-tubulin (β-TUB), RNA pol II (RP II), elongation factor-1 alpha (EF-1α), adenine phosphoribosyltransferase (APRT), TATA-binding protein-like factor (TLF), ubiquitin-conjugating enzyme 2 (UBC2), ubiquitin-conjugating enzyme E2L5 (UBC5) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were selected from mRNA sequences of E. crus-galli and E. colona var frumentacea. Five statistical algorithms (geNorm, NormFinder, BestKeeper, ΔCt, and RefFinder) were applied to determine the expression stabilities of these genes in barnyard millet grown under four different abiotic stress (drought, salinity, cold and heat) exposed at different time points. The UBC5 and ɑ-TUB in drought, GAPDH in salinity, GAPDH and APRT in cold, and EF-1α and RP II in heat were the most stable reference genes, whereas ß-TUB was the least stable irrespective of stress conditions applied. Further Vn/Vn + 1 analysis revealed two reference genes were sufficient to normalize gene expression across all sample sets. The suitability of identified reference genes was validated with Cu-ZnSOD (SOD1) in the plants exposed to different abiotic stress conditions. The results revealed that the relative quantification of the SOD1 gene varied according to reference genes and the number of reference genes used, thus highlighting the importance of the choice of a reference gene in such experiments. This study provides a foundational framework for standardizing RT-qPCR analyses, enabling accurate gene expression profiling in barnyard millet.

Identification and Validation of Reference Genes for RT-qPCR Analysis in Reed Canary Grass during Abiotic Stress

Reed canary grass (Phalaris arundinacea L.) is known for its tolerance to drought, heavy metals, and waterlogging, making it a popular choice for forage production and wetland restoration in the Qinghai-Tibet Plateau (QTP). To accurately assess gene expression in reed canary grass under different abiotic stresses, suitable reference genes need to be identified and validated. Thirteen candidate reference gene sequences were selected and screened using RT-qPCR to detect their expression levels in reed canary grass leaves under drought, salt, cadmium, and waterlogging stresses. Four algorithms were used to assess the stability of the expression levels of the candidate reference genes. The most stably expressed genes were UBC and H3 under drought Cd, ETF and CYT under salt stress, and ETF and TUB under waterlogging stress. GAPDH was found to be less stable under abiotic stresses. PIP-1, PAL, NAC 90, and WRKY 72A were selected as response genes for quantitative expression assessment under drought, salt, Cd, and waterlogging stresses to confirm the accuracy of the selected stable reference genes. These results provide a theoretical reference for assessing gene expression in reed canary grass under abiotic stresses.

Effects of Biological Nitrogen Metabolism on Glufosinate-Susceptible and -Resistant Goosegrass (Eleusine indica L.)

Glufosinate is a broad-spectrum herbicide used to control most weeds in agriculture worldwide. Goosegrass (Eleusine indica L.) is one of the top ten malignant weeds across the world, showing high tolerance to glufosinate via different mechanisms that are not yet fully understood. This study revealed that nitrogen metabolism could be a target-resistant site, providing clues to finally clarify the mechanism of glufosinate resistance in resistant goosegrass populations. Compared to susceptible goosegrass (NX), the resistant goosegrass (AUS and CS) regarding the stress of glufosinate showed stronger resistance with lower ammonia contents, higher target enzyme GS (glutamine synthetase) activity, and lower GOGAT (glutamine 2-oxoglutarate aminotransferase) activity. The GDH (glutamate dehydrogenase) activity of another pathway increased, but its gene expression was downregulated in resistant goosegrass (AUS). Analyzing the transcriptome and proteome data of goosegrass under glufosinate stress at 36 h showed that the KEGG pathway of the nitrogen metabolism was enriched in glufosinate-susceptible goosegrass (NX), but not in glufosinate-resistant goosegrass (CS and AUS). Several putative target genes involved in glufosinate stress countermeasures were identified. This study provides specific insights into the nitrogen metabolism of resistant goosegrass, and gives a basis for future functional verification of glufosinate-tolerance genes in plants.

Development of reference genes for RT-qPCR analysis of gene expression in Pleurotus pulmonarius for biotechnological applications

Jatropha curcas is an oilseed crop with biorefinery applications. Whilst cake generated following oil extraction offers potential as a protein source for animal feed, inactivation of toxic phorbol esters present in the material is necessary. Pleurotus pulmonarius is a detoxifying agent for jatropha cake with additional potential as animal feed, edible mushroom and for enzyme production. For the characterization of fungal genes involved in phorbol ester degradation, together with other industrial applications, reverse transcription-quantitative PCR (RT-qPCR) is a tool that enables accurate quantification of gene expression. For this, reliable analysis requires reference genes for normalization of mRNA levels validated under conditions employed for target genes. The stability of potential reference genes β-TUB, ACTIN, GAPDH, PHOS, EF1α, TRPHO, LAC, MNP3, MYP and VP were evaluated following growth of P. pulmonarius on toxic, non-toxic jatropha cake and a combined treatment, respectively. NormFinder and geNorm algorithms for expression stability analysis identified PHOS, EF1α and MNP3 as appropriate for normalizing gene expression. Reference gene combinations contrasting in ranking were compared following normalization of relative expression of the CHU_2040 gene, encoding an esterase enzyme potentially involved in phorbol ester degradation. The reference genes for P. pulmonarius will facilitate the elucidation of mechanisms involved in detoxification of phorbol esters as well as analysis of target genes for application in biorefinery models.

Selection and Evaluation of Reference Genes for RT-qPCR Analysis in Amorphophallus Konjac Based on Transcriptome Data

Combined with the Konjac transcriptome database of our laboratory and internal reference genes commonly used in plants, the eight candidate internal reference genes were screened and detected. They are the 25S ribosomal RNA gene (25S rRNA), 18S ribosomal RNA gene (18S rRNA), actin gene (ACT), glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), ubiquitin gene (UBQ), β-tubulin gene (β-TUB), eukaryotic elongation factor 1-αgene(eEF-1α), and eukaryotic translation initiation factor 4α-1 gene (eIF-4α). The results of GeNorm, Normfinder, and BestKeeper were analyzed comprehensively. The data showed that the expression levels of 25S rRNA, 18S rRNA, and ACT at the reproductive periods, eEF-1α and eIF-4α at the nutritional periods, and eEF-1α, UBQ, and ACT at different leaf developmental periods were stable. These identified and stable internal reference genes will provide the basis for the subsequent molecular biology-related studies of Konjac.

CRISPR/Cas9 mutants delineate roles of Populus FT and TFL1/CEN/BFT family members in growth, dormancy release and flowering

Vegetative and reproductive phase change and phenology are economically and ecologically important traits. Trees typically require several years of growth before flowering and, once mature, seasonal control of the transition to flowering and flower development is necessary to maintain vegetative meristems and for reproductive success. Members of two related gene subfamilies, FLOWERING LOCUST (FT) and TERMINAL FLOWER1 (TFL1)/CENTRORADIALIS (CEN)/BROTHER OF FT AND TFL1 (BFT), have antagonistic roles in flowering in diverse species and roles in vegetative phenology in trees, but many details of their functions in trees have yet to be resolved. Here, we used CRISPR/Cas9 to generate single and double mutants involving the five Populus FT and TFL1/CEN/BFT genes. The ft1 mutants exhibited wild-type-like phenotypes in long days and short days, but after chilling, to release dormancy, they showed delayed bud flush and GA3 could compensate for the ft1 mutation. After rooting and generating some phytomers in tissue culture, both cen1 and cen1ft1 mutants produced terminal as well as axillary flowers, indicating that the cen1 flowering phenotype is independent of FT1. The CEN1 showed distinct circannual expression patterns in vegetative and reproductive tissues and comparison with the expression patterns of FT1 and FT2 suggests that the relative levels of CEN1 compared with FT1 and FT2 regulate multiple phases of vegetative and reproductive seasonal development.

Genome-Wide Analysis of the Expansin Gene Family in Populus and Characterization of Expression Changes in Response to Phytohormone (Abscisic Acid) and Abiotic (Low-Temperature) Stresses

Expansins are a group of cell wall enzyme proteins that help to loosen cell walls by breaking hydrogen bonds between cellulose microfibrils and hemicellulose. Expansins are essential plant proteins that are involved in several key processes, including seed germination, the growth of pollen tubes and root hairs, fruit ripening and abscission processes. Currently, there is a lack of knowledge concerning the role of expansins in woody plants. In this study, we analyzed expansin genes using Populus genome as the study target. Thirty-six members of the expansin gene family were identified in Populus that were divided into four subfamilies (EXPA, EXPB, EXLA and EXLB). We analyzed the molecular structure, chromosome localization, evolutionary relationships and tissue specificity of these genes and investigated expression changes in responses to phytohormone and abiotic stresses of the expansin genes of Populus tremula L. (PtEXs). Molecular structure analysis revealed that each PtEX protein had several conserved motifs and all of the PtEXs genes had multiple exons. Chromosome structure analysis showed that the expansin gene family is distributed on 14 chromosomes. The PtEXs gene family expansion patterns showed segmental duplication. Transcriptome data of Populus revealed that 36 PtEXs genes were differently expressed in different tissues. Cis-element analysis showed that the PtEXs were closely associated with plant development and responses to phytohormone and abiotic stress. Quantitative real-time PCR showed that abscisic acid (ABA) and low-temperature treatment affected the expression of some PtEXs genes, suggesting that these genes are involved in responses to phytohormone and abiotic stress. This study provides a further understanding of the expansin gene family in Populus and forms a basis for future functional research studies.

Selection of reference genes for RT-qPCR analysis of rice with Rhizoctonia solani infection and biocontrol PGPR/KSi application

BACKGROUND

Rhizoctonia solani (AG1 IA) is an important pathogen of rice (Oryza sativa L.) that causes rice sheath blight (RSB). Since control of RSB by breeding and fungicides have had limited success, novel strategies like biocontrol with plant growth-promoting rhizobacteria (PGPR) can be an effective alternative.

METHOD AND RESULTS

Seven commonly used reference genes (RGs), 18SrRNA, ACT1, GAPDH2, UBC5, RPS27, eIF4a and CYP28, were evaluated for their stability in rice-R. solani-PGPR interaction for real-time quantitative PCR (RT-qPCR) analysis. Different algorithms were examined, Delta Ct, geNorm, NormFinder, BestKeeper, and comprehensive ranking by RefFinder, to evaluate RT-qPCR of rice in tissues infected with R. solani and treated with the PGPR strains, Pseudomonas saponiphilia and Pseudomonas protegens, with potassium silicate (KSi) alone or in combination with each PGPR strain. RG stability was affected for each treatment and treatment-specific RG selection was suggested. Validation analysis was done for nonexpressor of PR-1(NPR1) for each treatment.

CONCLUSION

Overall, ACT1 was the most stable RG with R. solani infection alone, GAPDH2 with R. solani infection plus KSi, UBC5 with R. solani infection plus P. saponiphilia, and eIF4a with R. solani infection plus P. protegens. Both ACT1 and RPS27 were the most stable with the combination of KSi and P. saponiphilia, while RPS27 was the most stable with the combination of KSi and P. protegens.

I Choose You: Selecting Accurate Reference Genes for qPCR Expression Analysis in Reproductive Tissues in Arabidopsis thaliana

Quantitative real-time polymerase chain reaction (qPCR) is a widely used method to analyse the gene expression pattern in the reproductive tissues along with detecting gene levels in mutant backgrounds. This technique requires stable reference genes to normalise the expression level of target genes. Nonetheless, a considerable number of publications continue to present qPCR results normalised to a single reference gene and, to our knowledge, no comparative evaluation of multiple reference genes has been carried out in specific reproductive tissues of Arabidopsis thaliana. Herein, we assessed the expression stability levels of ten candidate reference genes (UBC9, ACT7, GAPC-2, RCE1, PP2AA3, TUA2, SAC52, YLS8, SAMDC and HIS3.3) in two conditional sets: one across flower development and the other using inflorescences from different genotypes. The stability analysis was performed using the RefFinder tool, which combines four statistical algorithms (geNorm, NormFinder, BestKeeper and the comparative ΔCt method). Our results showed that RCE1, SAC52 and TUA2 had the most stable expression in different flower developmental stages while YLS8, HIS3.3 and ACT7 were the top-ranking reference genes for normalisation in mutant studies. Furthermore, we validated our results by analysing the expression pattern of genes involved in reproduction and examining the expression of these genes in published mutant backgrounds. Overall, we provided a pool of appropriate reference genes for expression studies in reproductive tissues of A. thaliana, which will facilitate further gene expression studies in this context. More importantly, we presented a framework that will promote a consistent and accurate analysis of gene expression in any scientific field. Simultaneously, we highlighted the relevance of clearly defining and describing the experimental conditions associated with qPCR to improve scientific reproducibility.

The Effect of Short-Term Heating on Photosynthetic Activity, Pigment Content, and Pro-/Antioxidant Balance of A. thaliana Phytochrome Mutants

The effects of heating (40 °C, 1 and 2 h) in dark and light conditions on the photosynthetic activity (photosynthesis rate and photosystem II activity), content of photosynthetic pigments, activity of antioxidant enzymes, content of thiobarbituric acid reactive substances (TBARs), and expression of a number of key genes of antioxidant enzymes and photosynthetic proteins were studied. It was shown that, in darkness, heating reduced CO₂ gas exchange, photosystem II activity, and the content of photosynthetic pigments to a greater extent in the phyB mutant than in the wild type (WT). The content of TBARs increased only in the phyB mutant, which is apparently associated with a sharp increase in the total peroxidase activity in WT and its decrease in the phyB mutant, which is consistent with a noticeable decrease in photosynthetic activity and the content of photosynthetic pigments in the mutant. No differences were indicated in all heated samples under light. It is assumed that the resistance of the photosynthetic apparatus to a short-term elevated temperature depends on the content of PHYB active form and is probably determined by the effect of phytochrome on the content of low-molecular weight antioxidants and the activity of antioxidant enzymes.

Screening and Verification of Reference Genes for Analysis of Gene Expression in Garlic (Allium sativum L.) under Cold and Drought Stress

The principal objective of this study was to screen and verify reference genes appropriate for gene expression evaluation during plant growth and development under distinct growth conditions. Nine candidate reference genes were screened based on garlic transcriptome sequence data. RT-qPCR was used to detect the expression levels of the aforementioned reference genes in specific tissues under drought and cold stress. Then, geNorm, NormFinder, BestKeeper, and ReFinder were used to consider the consistency of the expression levels of candidate reference genes. Finally, the stress-responsive gene expression of ascorbate peroxidase (APX) was quantitatively evaluated to confirm the chosen reference genes. Our results indicated that there were variations in the abundance and stability of nine reference gene transcripts underneath cold and drought stress, among which ACT and UBC-E2 had the highest transcript abundance, and 18S rRNA and HIS3 had the lowest transcript abundance. UBC and UBC-E2 were the most stably expressed genes throughout all samples; UBC and UBC-E2 were the most stably expressed genes during cold stress, and ACT and UBC were the most stably expressed genes under drought stress. The most stably expressed genes in roots, pseudostems, leaves, and cloves were EF1, ACT, HIS3, UBC, and UBC-E2, respectively, while GAPDH was the most unstable gene during drought and cold stress conditions and in exclusive tissues. Taking the steady reference genes UBC-E2, UBC, and ACT as references during drought and cold stress, the reliability of the expression levels was further demonstrated by detecting the expression of AsAPX. Our work thereby offers a theoretical reference for the evaluation of gene expression in garlic in various tissues and under stress conditions.

Selection of Novel Reference Genes by RNA-Seq and Their Evaluation for Normalising Real-Time qPCR Expression Data of Anthocyanin-Related Genes in Lettuce and Wild Relatives

Lettuce is a popular vegetable source of bioactive compounds, like anthocyanins, powerful antioxidants present in red and semi-red varieties. Selection of reliable reference genes (RGs) for the normalization of real-time quantitative PCR (qPCR) data is crucial to obtain accurate gene expression results. Among the genes with totally unrelated biological functions, six candidate RGs (ADF2, CYB5, iPGAM, SCL13, TRXL3-3, and VHA-H) with low variation in expression according to RNA-seq analyses, were selected for future expression studies of anthocyanin-related genes in three different experiments: leaf colour comparison (green vs. red) in commercial varieties; tissue comparison (leaf vs. stem) in a wild relative; and drought stress experiment in commercial and traditional varieties, and a wild relative. Expression profiles of the candidate RGs were obtained by qPCR and their stability was assessed by four different analytical tools, geNorm, NormFinder, BestKeeper, and Delta Ct method, all integrated in RefFinder. All results considered, we recommend CYB5 to be used as RG for the leaf colour experiment and TRXL3-3 for the tissue and drought stress ones, as they were the most stable genes in each case. RNA-seq is useful to preselect novel RGs although validation by qPCR is still advisable. These results provide helpful information for gene expression studies in Lactuca spp. under the described conditions.

Genome-Wide Comparative Analysis of the Fasciclin-like Arabinogalactan Proteins (FLAs) in Salicacea and Identification of Secondary Tissue Development-Related Genes

Fasciclin-like arabinogalactan proteins (FLAs) are a subclass of arabinogalactan proteins (AGPs) containing both AGP-like glycated domains and fasciclin (FAS) domains, which are involved in plant growth and development and synthesis of the cell wall. However, these proteins have not been identified or analyzed in willow, Salix, the sister genus of Populus. In this study, we performed a whole genome study of the FLA gene family of Salix suchowensis and compared it with the FLA gene family of Populus deltoides. The results showed the presence of 40 and 46 FLA genes in P. deltoides and S. suchowensis, distributed on 17 and 16 chromosomes, respectively. Four pairs of tandem repeat genes were found in willow, while poplar had no tandem repeat genes. Twelve and thirteen pairs of duplicated gene fragments were identified in poplar and willow, respectively. The multispecies phylogenetic tree showed that the FLA gene family could be divided into four groups (I-IV), with Group 1 showing significant expansion in woody plants. A gene expression analysis showed that PdeFLA19/27 in Group I of poplar was highly expressed, specifically during the secondary growth period of the stem and the rapid elongation of seed hairs. In the Group I genes of S. suchowensis, SsuFLA25/26/28 was also highly expressed during the secondary growth period, whereas increased expression of SsuFLA35 was associated with seed hair tissue. These results provide important clues about the differences in the FLA gene family during the evolution of herbs and woody plants, and suggest that the FLA gene family may play an essential role in regulating the secondary growth of woody plants. It also provides a reference for further studies on the regulation of secondary growth and seed hair development by FLA genes in poplar and willow.

Gene Expression Analysis by Quantitative Real-Time PCR for Floral Tissues

Real-time, or quantitative, reverse transcription polymerase chain reaction (qRT-PCR) is a powerful method for rapid and reliable quantification of mRNA abundance. Although it has not featured prominently in flower development research in the past, the availability of novel techniques for the synchronized induction of flower development, or for the isolation of cell-specific mRNA populations, suggests that detailed quantitative analyses of gene expression over time and in specific tissues and cell types by qRT-PCR will become more widely used. In this chapter, we discuss specific considerations for studying gene expression by using qRT-PCR, such as the identification of suitable reference genes for the experimental set-up used. In addition, we provide protocols for performing qRT-PCR experiments in a multiwell plate format (with the LightCycler® 480 system, Roche) and with nanofluidic arrays (BioMark™ system, Fluidigm), which allow the automatic combination of sets of samples with sets of assays, and significantly reduce reaction volume and the number of liquid-handling steps performed during the experiment.

Selection and validation of appropriate reference genes for RT-qPCR analysis of Nitraria sibirica under various abiotic stresses

BACKGROUND

Nitraria sibirica Pall. is a halophytic shrub with strong environmental adaptability that can survive in extremely saline-alkali and drought-impacted environments. Gene expression analysis aids in the exploration of the molecular mechanisms of plant responses to abiotic stresses. RT-qPCR is the most common technique for studying gene expression. Stable reference genes are a prerequisite for obtaining accurate target gene expression results in RT-qPCR analysis.

RESULTS

In this study, a total of 10 candidate reference genes were selected from the transcriptome of N. sibirica, and their expression stability in leaves and roots under different treatment conditions (salt, alkali, drought, cold, heat and ABA) was evaluated with the geNorm, NormFinder, BestKeeper, comparative ΔCt and RefFinder programs. The results showed that the expression stability of the candidate reference genes was dependent on the tissue and experimental conditions tested. ACT7 combined with R3H, GAPDH, TUB or His were the most stable reference genes in the salt- or alkali-treated leaves, salt-treated roots and drought-treated roots, respectively; R3H and GAPDH were the most suitable combination for drought-treated leaves, heat-treated root samples and ABA-treated leaves; DIM1 and His maintained stable expression in roots under alkali stress; and TUB combined with R3H was stable in ABA-treated roots. TBCB and GAPDH exhibited stable expression in heat-treated leaves; TBCB, R3H, and ERF3A were stable in cold-treated leaves; and the three most stable reference genes for cold-treated roots were TBCB, ACT11 and DIM1. The reliability of the selected reference genes was further confirmed by evaluating the expression patterns of the NsP5CS gene under the six treatment conditions.

CONCLUSION

This study provides a theoretical reference for N. sibirica gene expression standardization and quantification under various abiotic stress conditions and will help to reveal the molecular mechanisms that confer stress tolerance to N. sibirica.

Identification of Reliable Reference Genes under Different Stresses and in Different Tissues of Toxicodendron succedaneum

Toxicodendron succedaneum (L.) Kuntze (T. succedaneum) is an economic tree species that produces urushiol and urushi wax, and it is of great value in industry and medicine. However, the stability of reference genes (RGs) has not been systematically reported in T. succedaneum to date. In this study, the expression of 10 candidate RGs was analyzed by RT-qPCR in different tissues (roots, stems, leaves), stress treatments (high/low temperature, drought), and hormone stimulation (jasmonic acid, JA). Then, the stability ranking of 10 candidate genes was evaluated by ∆Ct analysis and three software programs: geNorm, NormFinder, and BestKeeper. Finally, RefFinder was used to comprehensively analyze the expression stability of 10 candidate genes. The comprehensive analysis showed that TsRG05/06, TsRG01/06, and TsRG03/ACT were stable under high/low-temperature stress, drought stress, and JA treatment, respectively. TsRG03 and ACT had stable expression in different tissues. While the TsRG03 and ACT were recommended as the suitable RGs for T. succedaneum in all samples. Meanwhile, UBQ was the least suitable as a reference gene for T. succedaneum. In addition, the results of geNorm showed that the combination of two stable RGs could make the results of gene expression more accurate. These results provide alternative RGs for the study of gene function, correction, and normalization of target gene expression and directed molecular breeding in T. succedaneum.

Validation of Reference Genes in a Population of Blueberry (Vaccinium corymbosum) Plants Regenerated in Colchicine

For the first time we report the validation of reference genes in plants from a population of blueberry (Vaccinium corymbosum) clones cultured in vitro on a colchicine-supplemented medium. Nodal segment explants of the cultivar Duke were regenerated by organogenesis under different periods of colchicine 1 mg/L exposure (1, 2, 3, 5, 30 days). The clones selected for the study showed variability for phenotypic traits after 2 years of adaptation to field conditions, compared to plants of the donor genotype that were regenerated on a medium without colchicine. Vaccinium myrtillus (GAPDH) and Vaccinium macrocarpon (ATP1, NADH, RPOB and COX2) were used as reference genomes for primer design. The results show that colchicine treatments can cause genomic changes in blueberry plants. At the molecular level, exposure of plants to colchicine in early periods could promote an increase in gene expression of specific genes such as ATP1, COX2, GAPDH, MATK, NADH and RPOB. However, prolonged exposure (30 days) could decrease gene expression of the genes studied. For qPCR assays, the primers designed for ATP1, COX2, GAPDH and MATK genes showed high efficiency. In addition, the GAPDH, ATP1, NADH and COX2 genes showed high stability and could be recommended as potential reference genes for gene expression assays in Vaccinium.

Genome-wide identification and analysis of LOX genes in soybean cultivar “Zhonghuang 13”

Lipoxygenases (LOXs; EC1.13.11.12) are a family of iron- or manganese-containing dioxygenases that catalyze the oxygenation of polyunsaturated fatty acids (PUFAs) and play important roles in plant growth, development, and stress response. In this study, a total of 36 LOX gene family members were identified and annotated in Zhonghuang 13, a soybean cultivar bred by Chinese scientists in 2001. Sanger sequencing of the GmLOX1-coding sequence and colorimetric assays for the GmLOX1 protein showed that Zhonghuang 13 possessed the GmLOX1 gene. These LOX genes are divided into three subfamilies: 9-LOX, type Ⅰ 13-LOX and type II 13-LOX. In the 13-LOX group, the number of GmLOX members was the highest. These GmLOX genes are unevenly distributed on chromosomes 3, 7, 8, 10, 11, 12, 13, 15, 16, 19, and 20. Most of the 13-LOX genes exist in the form of gene clusters, indicating that these genes may originate from tandem duplications. The analysis of duplicated gene pairs showed that GmLOX genes underwent purifying selective pressure during evolution. The gene structures and conserved functional domains of these genes are quite similar. Compared to the orthologous gene pairs of LOX genes between wild soybean (Glycine soja W05) and Zhonghuang 13, the sequences of most gene pairs are relatively conserved. Many cis-elements are present in the promoter region and are involved in stress response, growth and development, hormone response and light response. The tissue-specific gene expression of GmLOX genes was evaluated. Represented by GmLOX1, GmLOX2, and GmLOX3, which were expressed at extremely high levels in seeds, they showed the characteristics of specific expression. This study provides detailed information on soybean lipoxygenase gene family members in Zhonghuang 13, which lays a foundation for further research.

Evaluation and validation of reference genes in Cymbidium faberi for real-time quantitative PCR

For all organs at all Cymbidium faberi stages, ACT, UBQ3 and GAPDH can be selected as reference genes. For organs of the vegetative stage, UBQ2 and UBQ3 can be chosen for analysis of normalized gene expression. For the bud stage, ACT and UBQ3 can be used for analysis of gene expression. For the full blossom stage, ACT, UBQ3 and UBQ2 can be introduced into relative gene expression analysis. For vegetative organs, UBQ2 and ACT can be used as reference genes. For reproductive organs, ACT, UBQ3 and UBQ2 can be used as a reference for data processing. CfAG1 gene expression is more consistent when UBQ3, GAPDH and ACT are used as reference genes.

Reference gene identification for normalisation of RT-qPCR analysis in plasma samples of the rat middle cerebral artery occlusion model

OBJECTIVE

In quantitative reverse transcription-polymerase chain reaction (RT-qPCR) studies, the selection and validation of reference genes are crucial for the accurate analysis of MicroRNAs (miRNAs) expression. In this work, the optimal reference genes for RT-qPCR normalisation in plasma samples of rat middle cerebral artery occlusion (MCAO) models were identified.

METHODS

Six rat MCAO models were established. Blood samples were collected before modelling and approximately 16-24 h after modelling. Two commonly used reference genes (U6 and 5S) and three miRNAs (miR-24, miR-122 and miR-9a) were selected as candidate reference genes, and the expression of these genes was detected with RT-qPCR. The acquired data were analysed using geNorm, Normfinder, BestKeeper, RefFinder and comparative delta threshold cycle statistical models.

RESULTS

The analysed results consistently showed that miR-24 was the most stably expressed reference gene. The 'optimal combination' calculated by geNorm was miR-24, U6 and5S. The expression level of the target gene miR124 was similar when the most stable reference gene miR-24 or the 'optimal combination' was used as a reference gene. However, compared with miR24 or the 'optimal combination', the less stable reference genes influenced the fold change and the data accuracy with a large standard deviation.

CONCLUSION

These results confirmed the importance of selecting suitable reference genes for normalisation to obtain reliable results in RT-qPCR studies and demonstrated that the identified reference gene miR-24 or the 'optimal combination' could be used as an internal control for gene expression analysis in the rat MCAO model.

Validation of reference genes as an internal control for studying Avena sativa-Puccinia coronata interaction by RT-qPCR

In this study we evaluated eleven candidate reference genes in Avena sativa during compatible and incompatible interactions with two different pathotypes of Puccinia coronata f. sp. avenae in six time points post-inoculation. The identification of genes with high expression stability was performed by four algorithms (geNorm, NormFinder, BestKeeper and ΔCt method). The results obtained confirmed that the combination of two genes would be sufficient for reliable normalization of the expression data. In general, the most stable in the tested plant-pathogen system were HNR (heterogeneous nuclear ribonucleoprotein 27C) and EF1A (elongation factor 1-alpha). ARF (ADP-ribosylation factor) and EIF4A (eukaryotic initiation factor 4A-3) could also be considered as exhibiting high expression stability. CYP (cyclophilin) was shown by all assessment methods to be the worst candidate for normalization in this dataset. To date, this is the first report of reference genes selection in A. sativa–P. coronata interaction system. Identified reference genes enable reliable and comprehensive RT-qPCR analysis of oat gene expression in response to crown rust infection. Understanding the molecular mechanisms involved in the host–pathogen interactions may expand knowledge of durable resistance strategies beneficial to modern oat breeding.

Selection of potential reference genes for RT-qPCR in the plant pathogenic fungus Colletotrichum fructicola

Colletotrichum is widespread, and these pathogenic fungi can cause various plant diseases. Studies have shown that Colletotrichum fructicola cause oil-tea (Camellia oleifera) anthracnose and is widely distributed as a dominant fungus in all Ca. oleifera-producing regions. Real-time quantitative PCR(RT-qPCR) is considered the most reliable technique for simultaneously measuring relative gene expression levels in different tissues. Target genes are typically quantified using RT-qPCR to explore gene function, and reliable RT-qPCR results require data normalization using stable reference genes. No studies have reported a suitable reference gene in C. fructicola. This study has eight candidate reference genes (CfCk, CfRpp, CfUce, CfRrp, CfAdrh, CfDd, CfAct, and CfTub) which were selected from C. fructicola-Ca. oleifera transcriptome data and evaluated and sequenced using geNorm, NormFinder, and BestKeeper algorithms. The results showed that CfRrp had better stability in C. fructicola, both during the growth of pure pathogenic fungi and during the invasion of different oil-tea leaves. After normalization with CfRrp, the differentially expressed target genes were similar to the transcriptome. Our work provides suitable reference genes for future studies to quantify target gene expression levels in C. fructicola.

Evaluation of reference genes for transcript normalization in Fragaria chiloensis fruit and vegetative tissues

Quantitative real-time PCR (RT-qPCR) is used extensively in gene expression studies. For adequate comparisons, the identification and use of reliable reference genes are crucial. Nevertheless, the availability of such genes in strawberry species is limited and has yet to be described for the Chilean strawberry, Fragaria chiloensis. In this study, the expression dynamics of a set of 10 candidate reference genes were analyzed in various F. chiloensis vegetative tissues (root, runners, stem, leaf, and flower), and fruits at different ripening stages or subjected to different hormonal treatments (ABA, auxin). The expression stability of candidate genes was examined by a series of algorithms, such as geNorm, NormFinder, BestKeeper, and ΔCt, for comparisons and rankings. Finally, by using RefFinder, a comprehensive and comparative ranking of the four methods was achieved. The results highlight that the expression stability of candidate reference genes fluctuates depending on tissue type, fruit stage, and hormonal treatment. As reference genes, the use of FcCHP2 and FcACTIN1 is recommended for F. chiloensis vegetative tissues; FcDBP and FcCHP1 for fruit ripening stages; FcGAPDH and FcDBP for fruit subjected to ABA and NDGA treatments; FcCHP1 and FcCHP2 for fruit under AUXIN and TIBA treatments; and FcDBP and FcCHP2 when all fruit stages and hormonal treatments are compared. If just one reference gene is employed as a normalizer, FcDBP should be chosen as it is the most stable internal control in most conditions. Therefore, the present study delivers a set of reliable reference genes for RT-qPCR expression analysis in F. chiloensis tissues and fruits subjected to several hormonal treatments.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01227-y.

GhWRKY33 Interacts with GhTIFY10A to Synergistically Modulate Both Ageing and JA-Mediated Leaf Senescence in Arabidopsis

WRKY transcription factors play critical roles in the modulation of transcriptional changes during leaf senescence, but the underlying mechanisms controlled by them in this progress still remain enigmatic. In this study, Gossypium hirsutum WRKY DNA-binding protein 33 (GhWRKY33) was characterized as a negative regulator of both ageing and JA-mediated leaf senescence. The overexpression of GhWRKY33 in Arabidopsis greatly delayed leaf senescence, as determined by elevated chlorophyll content, lower H₂O₂ content, and reduced expression of several senescence-associated genes (SAGs). An electrophoretic mobility shift assay (EMSA) and transient dual–luciferase reporter assay revealed that GhWRKY33 could bind to the promoters of both AtSAG12 and Ghcysp and suppress their expression. Yeast two-hybrid (Y2H) and firefly luciferase complementation imaging (LUC) assays showed that GhWRKY33 could interact with GhTIFY10A. Similarly, the overexpression of GhTIFY10A in Arabidopsis also dramatically delayed leaf senescence. Furthermore, both GhWRKY33 and GhTIFY10A negatively regulate JA-mediated leaf senescence. In addition, a transientdual-luciferase reporter assay indicated that GhWRKY33 and GhTIFY10A could function synergistically to inhibit the expression of both AtSAG12 and Ghcysp. Thus, our work suggested that GhWRKY33 may function as a negative regulator to modulate both ageing and JA-mediated leaf senescence and also contributes to a basis for further functional studies on cotton leaf senescence.

Identification of Reference Genes for RT-qPCR Analysis in Gleditsia microphylla under Abiotic Stress and Hormone Treatment

Gleditsia microphylla is an important galactomannan gums source plant with characteristics of drought resistance, barren tolerance, and good adaptability. However, the underlying molecular mechanisms of the biological process are not yet fully understood. Real-time quantitative PCR (RT-qPCR) is an accurate and convenient method to quantify the gene expression level and transcription abundance of suitable reference genes. This study aimed to screen the best internal reference genes in G. microphylla under abiotic stresses, hormone treatments, and different tissues. Based on the transcriptome data, twelve candidate reference genes were selected, and ultimately, nine of them were further evaluated by the geNorm, NormFinder, BestKeeper, and RefFinder algorithms. These results show that TATA-binding protein 1 (TBP1)and Eukaryotic translation initiation factor 4A1 (EIF4A1)were the two most stable reference genes, and glyceraldehyde-3-phosphate dehydrogenase A subunit, chloroplastic (GAPA)and glyceraldehyde-3-phosphate dehydrogenase B subunit, chloroplastic (GAPB)were the two most unstable reference genes across all samples under the given experimental conditions. Meanwhile, the most stable reference genes varied among the different groups and tissues. Therefore, this study suggests that it is better to use a specific reference gene for a particular case rather than using a common reference gene.

Selection and validation of reference genes for quantitative real-time PCR normalization in Psoralea corylifolia (Babchi) under various abiotic stress

Psoralea corylifolia L. is a popular herb and has long been used in traditional Ayurvedic and Chinese medicine owing to its extensive pharmacological activities, especially in the treatment of various shin diseases. To date, the systematic evaluation and selection of the optimum reference genes for gene expression analysis of P. corylifolia were not reported. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is a method for gene expression quantification. Selecting appropriate reference genes is the prerequisite for accurate normalization of RT-qPCR results. This study assessed the expression stability of 10 candidate reference genes under different abiotic stresses. First, amplification primers for RT-qPCR were designed and received testing and optimization. Then, expression data from each candidate gene were evaluated based on three statistical algorithms, and their results were further integrated into a comprehensive ranking based on the geometric mean. Additionally, one target gene, i.e., 1-aminocyclopropane-1-carboxylate oxidase (ACO), was used to validate the effectiveness of the selected reference. Our analysis suggested that thioredoxin-like protein YLS8 (YLS8), TIP41-like family protein (TIP41), and cyclophilin 2 (CYP2) genes provided superior expression normalization under different abiotic stresses. Overall, this work constitutes the first effort to select optimal endogenous controls for RT-qPCR studies of gene expression in P. corylifolia. It also provides a reasonable normalization standard and basis for further analysis of the gene expression of bioactive components in P. corylifolia.

Molecular basis of differential adventitious rooting competence in poplar genotypes

Recalcitrant adventitious root (AR) development is a major hurdle in propagating commercially important woody plants. Although significant progress has been made to identify genes involved in subsequent steps of AR development, the molecular basis of differences in apparent recalcitrance to form AR between easy-to-root and difficult-to-root genotypes remains unknown. To address this, we generated cambium tissue-specific transcriptomic data from stem cuttings of hybrid aspen, T89 (difficult-to-root) and hybrid poplar OP42 (easy-to-root), and used transgenic approaches to verify the role of several transcription factors in the control of adventitious rooting. Increased peroxidase activity was positively correlated with better rooting. We found differentially expressed genes encoding reactive oxygen species scavenging proteins to be enriched in OP42 compared with T89. A greater number of differentially expressed transcription factors in cambium cells of OP42 compared with T89 was revealed by a more intense transcriptional reprograming in the former. PtMYC2, a potential negative regulator, was less expressed in OP42 compared with T89. Using transgenic approaches, we demonstrated that PttARF17.1 and PttMYC2.1 negatively regulate adventitious rooting. Our results provide insights into the molecular basis of genotypic differences in AR and implicate differential expression of the master regulator MYC2 as a critical player in this process.

Gapdh Shows Altered Gene Expression in Alcohol Models

Background and objectives. Though glyceraldehyde-3-phosphate dehydrogenase (Gapdh) is one of the most commonly used housekeeping genes for comparison of gene expression data, studies have revealed that Gapdh expression is not constant at different developmental stages, and is modulated by many factors including ethanol. In view of this, in the present study, we investigated the effect of ethanol on Gapdh stability and expression levels in different model systems.

Methods. Evaluation of Gapdh stability was determined by comparison with three commonly used housekeeping genes in alcohol-exposed and control mouse blastocysts, embryos, and placentas (ActB, Hsp90ab1, and Atp5b), and in alcohol-dependent and healthy humans (ACTB, ATP5B, and HSPCB), and was ranked by the software program RefFinder. To detect the Gapdh expression patterns as a target gene, qRT-PCR analysis was applied.

Results. The order of expression stabilities obtained by the RefFinder ranked Gapdh as the most unstable reference gene in studied groups. The study of the expression dynamics of Gapdh showed significant upregulation in ethanol-exposed mouse blastocysts and embryos (FC = 1.56, p = 0.05 and FC = 6.0, p = 0.01) and downregulation in placentas (FC = 0.60, p = 0.01).

Conclusions. Our results revealed that the expression of Gapdh can vary in different model systems under ethanol exposure and imply the need for caution when using it as an internal control. This is the first report for statistically significant change in Gapdh expression after ethanol exposure during preimplantation mouse development.

Selection and Validation of Reference Genes for RT-qPCR Analysis in Tibetan Medicinal Plant Saussurea Laniceps Callus under Abiotic Stresses and Hormone Treatments

Real-time quantitative PCR (RT-qPCR) is an important technique for studying gene expression analysis, but accurate and reliable results depend on the use of a stable reference gene. This study proposes to test the expression stability of candidate reference genes in the callus of Saussurea laniceps, a unique Tibetan medicinal plant. Based on the S. laniceps callus transcriptome, eleven candidate reference genes, including TUA2, TUB3, TUB8, TIF3B1, TIF3H1, ELF5A, PP2AA2, UEV1D, UBL5, UBC36, and SKIP1), were validated for RT-qPCR normalization in the callus under abiotic stress (salt, cold, and UV) and hormone treatments (abscisic acid, MeJA, and salicylic acid). The stability of the candidate genes was evaluated in all the samples of S. laniceps. Comprehensive analysis of all samples showed that the best reference genes were UBC36 and UBL5. ELF5A and TIF3B1 were ranked as the most stable genes in the sample sets under abiotic stress. For hormone stimulation, UBC36 and TIF3H1 genes had the best stability. This study provides useful guidelines and a starting point for reference gene selection for expression analysis using RT-qPCR techniques in S. laniceps.

Linalool Activates Oxidative and Calcium Burst and CAM3-ACA8 Participates in Calcium Recovery in Arabidopsis Leaves

Plants produce linalool to respond to biotic stress, but the linalool-induced early signal remains unclear. In wild-type Arabidopsis, plant resistance to diamondback moth (Plutella xylostella) increased more strongly in a linalool-treated group than in an untreated control group. H₂O₂ and Ca²⁺, two important early signals that participated in biotic stress, burst after being treated with linalool in Arabidopsis mesophyll cells. Linalool treatment increased H₂O₂ and intracellular calcium concentrations in mesophyll cells, observed using a confocal microscope with laser scanning, and H₂O₂ signaling functions upstream of Ca²⁺ signaling by using inhibitors and mutants. Ca²⁺ efflux was detected using non-invasive micro-test technology (NMT), and Ca²⁺ efflux was also inhibited by NADPH oxidase inhibitor DPI (diphenyleneiodonium chloride) and in cells of the NADPH oxidase mutant rbohd. To restore intracellular calcium levels, Ca²⁺-ATPase was activated, and calmodulin 3 (CAM3) participated in Ca²⁺-ATPase activation. This result is consistent with the interaction between CAM7 and Ca²⁺-ATPase isoform 8 (ACA8). In addition, a yeast two-hybrid assay, firefly luciferase complementation imaging assay, and an in vitro pulldown assay showed that CAM3 interacts with the N-terminus of ACA8, and qRT-PCR showed that some JA-related genes and defense genes expressions were enhanced when treated with linalool in Arabidopsis leaves. This study reveals that linalool enhances H₂O₂ and intracellular calcium concentrations in Arabidopsis mesophyll cells; CAM3-ACA8 reduces intracellular calcium concentrations, allowing cells to resume their resting state. Additionally, JA-related genes and defense genes' expression may enhance plants' defense when treated with linalool.

Evaluation of reference genes for RT-qPCR gene expression analysis in Arabidopsis thaliana exposed to elevated temperatures

Increases in environmental temperature are directly linked to the issue of climate change and are known to significantly disrupt plant growth and development. Studies of gene expression in plants commonly include RT-qPCR but the reliability of the method depends on the use of suitable reference genes for data normalization. Despite this, no reference genes have been validated specifically for experiments in Arabidopsis thaliana employing treatments with elevated temperature. Here, ten genes were selected for expression stability analysis based on the screening of available literature and microarray data from temperature-treated A. thaliana. Expression levels of candidate reference genes were measured in 12-day-old seedlings, rosette leaves and flower buds of 5-week-old A. thaliana plants exposed to five different temperatures (22°C, 27°C, 32°C, 37°C and 42°C) and their expression stabilities were assessed using four statistical algorithms (BestKeeper, geNorm, NormFinder and comparative ΔC_q method). This study provides reliable reference genes for use in A. thaliana RT-qPCR expression analyses employing elevated temperature treatments, namely OGIO and PUX7 in seedlings, UBC21 and PUX7 in leaves, TIP41 and UBC21 in buds, and TIP41 and UBC21 in all three tissues combined. Orthologues of these genes can be of potential use in less studied plants, especially agricultural species heavily affected by climate change.

A Selection of Reliable Reference Genes for Gene Expression Analysis in the Female and Male Flowers of Salix suchowensis

Salix is a dioecious plant. Research on the molecular regulation mechanism of male and female inflorescence differentiation and development is necessary to analyze sex differentiation in the willow and the underlying mechanisms of unisexual flower development. However, at present, there are no reference genes suitable for stable expression in the process of willow inflorescence development. In this study, Salix suchowensis was used as the research material, nine candidate reference genes (α-TUB1, α-TUB2, ACT, H2A, DnaJ, CDC2, GAPDH, TIP41, β-TUB) were selected, and qRT-PCR technology was used to detect the expression of each candidate reference gene in female and male flowers at different developmental stages and using five algorithms (geNorm, Normfinder, Delta Ct, BestKeeper, and RefFinder) to comprehensively evaluate the stability of candidate reference genes. The results showed that ACT and DnaJ were stably expressed in all samples and could be used as reference genes. In addition, the reliability of the screening results was further verified via an expression pattern analysis of the CFS gene that encodes flower specific transcription factor in different samples. The stable reference genes selected in this study provide the basis for future research on the expression analysis of functional genes related to the development of male and female flowers of S. suchowensis.

CabHLH79 Acts Upstream of CaNAC035 to Regulate Cold Stress in Pepper

Cold stress is one of the main restricting factors affecting plant growth and agricultural production. Complex cold signaling pathways induce the expression of hundreds of cold-sensitive genes. The NAC transcription factor CaNAC035 has previously been reported to significantly influence the response of pepper to cold stress. Here, using Yeast one-hybrid (Y1H) library screened to search for other relevant molecular factors, we identified that CabHLH79 directly binds to the CaNAC035 promoter. Different basic helix–loop–helix (bHLH) transcription factors (TFs) in plants significantly respond to multiple plant stresses, but the mechanism of bHLHs in the cold tolerance of pepper is still unclear. This study investigated the functional characterization of CabHLH79 in the regulation of cold resistance in pepper. Down-regulation of CabHLH79 in pepper by virus-induced gene silencing (VIGS) increased its sensitivity to low temperature, whereas overexpression of CabHLH79 in pepper or Arabidopsis enhanced cold resistance. Compared with control plants, VIGS mediated of CabHLH79 had lower enzyme activity and related gene expression levels, accompanied by higher reactive oxygen species (ROS) accumulation, relative electrolyte leakage (REL), and malondialdehyde accumulation (MDA) contents. Transient overexpression of CabHLH79 pepper positively regulated cold stress response genes and ROS genes, which reduced REL and MDA contents. Similarly, ectopic expression of CabHLH79 in Arabidopsis showed less ROS accumulation, and higher enzymes activities and expression levels. These results indicated that CabHLH79 enhanced cold tolerance by enhancing the expression of ROS-related and other cold stress tolerance-related genes. Taken together, our results showed a multifaceted module of bHLH79-NAC035 in the cold stress of pepper.

The Landscape of Autophagy-Related (ATG) Genes and Functional Characterization of TaVAMP727 to Autophagy in Wheat

Autophagy is an indispensable biological process and plays crucial roles in plant growth and plant responses to both biotic and abiotic stresses. This study systematically identified autophagy-related proteins (ATGs) in wheat and its diploid and tetraploid progenitors and investigated their genomic organization, structure characteristics, expression patterns, genetic variation, and regulation network. We identified a total of 77, 51, 29, and 30 ATGs in wheat, wild emmer, T. urartu and A. tauschii, respectively, and grouped them into 19 subfamilies. We found that these autophagy-related genes (ATGs) suffered various degrees of selection during the wheat’s domestication and breeding processes. The genetic variations in the promoter region of Ta2A_ATG8a were associated with differences in seed size, which might be artificially selected for during the domestication process of tetraploid wheat. Overexpression of TaVAMP727 improved the cold, drought, and salt stresses resistance of the transgenic Arabidopsis and wheat. It also promoted wheat heading by regulating the expression of most ATGs. Our findings demonstrate how ATGs regulate wheat plant development and improve abiotic stress resistance. The results presented here provide the basis for wheat breeding programs for selecting varieties of higher yield which are capable of growing in colder, drier, and saltier areas.

Gene Expression Studies in Formalin-Fixed Paraffin-Embedded Samples of Cutaneous Cancer: The Need for Reference Genes

Formalin-fixed paraffin-embedded (FFPE) tumour samples may provide crucial data regarding biomarkers for neoplasm progression. Analysis of gene expression is frequently used for this purpose. Therefore, mRNA expression needs to be normalized through comparison to reference genes. In this study, we establish which of the usually reported reference genes is the most reliable one in cutaneous malignant melanoma (MM) and cutaneous squamous cell carcinoma (CSCC). ACTB, TFRC, HPRT1 and TBP expression was quantified in 123 FFPE samples (74 MM and 49 CSCC biopsies) using qPCR. Expression stability was analysed by NormFinder and Bestkeeper softwares, and the direct comparison method between means and SD. The in-silico analysis with BestKeeper indicated that HPRT1 was more stable than ACTB and TFRC in MM (1.85 vs. 2.15) and CSCC tissues (2.09 vs. 2.33). The best option to NormFinder was ACTB gene (0.56) in MM and TFRC (0.26) in CSCC. The direct comparison method showed lower SD means of ACTB expression in MM (1.17) and TFRC expression in CSCC samples (1.00). When analysing the combination of two reference genes for improving stability, NormFinder indicated HPRT1 and ACTB to be the best for MM samples, and HPRT1 and TFRC genes for CSCC. In conclusion, HPRT1 and ACTB genes in combination are the most appropriate choice for normalization in gene expression studies in MM FFPE tissue, while the combination of HPRT1 and TFRC genes are the best option in analysing CSCC FFPE samples. These may be used consistently in forthcoming studies on gene expression in both tumours.