PECTIN ACETYLESTERASE12 regulates shoot branching via acetic acid and auxin accumulation in alfalfa shoots.

Shoot branching is an important biological trait affecting alfalfa (Medicago sativa L.) production, but its development is complicated and the mechanism is not fully clear. In the present study, pectin acetylesterase 12 (MsPAE12) and NAM/ATAF/CUC-domain transcription factor gene (MsNAC73) were isolated from alfalfa. MsPAE12 was highly expressed in shoot apexes, and MsNAC73 was found to be a key transcriptional repressor of MsPAE12 by directly binding to salicylic acid (SA) and jasmonic acid (JA) elements in the MsPAE12 promoter. The biological functions of MsPAE12 and MsNAC73 were studied through overexpression (OE) and down-expression (RNAi) of the 2 genes in alfalfa. The numbers of shoot branches increased in MsPAE12-OE lines but decreased in MsPAE12-RNAi and MsNAC73-OE plants, which was negatively related to their indole-3-acetic acid (IAA) accumulation in shoot apexes. Furthermore, the contents of acetic acid (AA) in shoot apexes decreased in MsPAE12-OE plants but increased in MsPAE12-RNAi and MsNAC73-OE plants. The changes of AA contents were positively related to the expression of TRYPTOPHAN AMINOTRANSFERASE 1 (MsTAA1), TRYPTOPHAN AMINOTRANSFERASE-RELATED 2 (MsTAR2), and YUCCA flavin monooxygenase (MsYUCC4) and the contents of tryptophan (Trp), indole-3-pyruvic acid (IPA), and IAA in shoot apexes of MsPAE12-OE, MsPAE12-RNAi, and MsNAC73-OE plants. Exogenous application of AA to wild type (WT) and MsPAE12-OE plants increased Trp, IPA, and IAA contents and decreased branch number. Exogenous IAA suppressed shoot branching in MsPAE12-OE plants, but exogenous IAA inhibitors increased shoot branching in MsPAE12-RNAi plants. These results indicate that the MsNAC73-MsPAE12 module regulates auxin-modulated shoot branching via affecting AA accumulation in shoot apexes of alfalfa.

The MsDHN1-MsPIP2;1-MsmMYB module orchestrates the trade-off between growth and survival of alfalfa in response to drought stress.

Dehydrins and aquaporins play crucial roles in plant growth and stress responses by acting as protector and controlling water transport across membranes, respectively. MsDHN1 (dehydrin) and MsPIP2;1 (aquaporin) were demonstrated to interact with a membrane-anchored MYB protein, MsmMYB (as mMYB) in plasma membrane under normal condition. MsDHN1, MsPIP2;1 and MsDHN1-MsPIP2;1 positively regulated alfalfa tolerance to water deficiency. Water deficiency caused phosphorylation of MsPIP2;1 at Ser 272, which led to release C terminus of mMYB (mMYBΔ83) from plasma membrane and translocate to nucleus, where C terminus of MsDHN1 interacted with mMYBΔ83, and promoted mMYBΔ83 transcriptional activity in response to water deficiency. Overexpression of mMYB and mMYBΔ83 down-regulated the expression of MsCESA3, but up-regulated MsCESA7 expression by directly binding to their promoters, and resulted in high drought tolerance in transgenic hairy roots. These results indicate that the MsDHN1-MsPIP2;1-MsMYB module serves as a key regulator in alfalfa against drought stress.

Chloroplast-targeted late embryogenesis abundant 1 increases alfalfa tolerance to drought and aluminum.

Late embryogenesis-abundant (LEA) proteins are important stress-response proteins that participate in protecting plants against abiotic stresses. Here, we investigated LEA group 3 protein MsLEA1, containing the typically disordered and α-helix structure, via overexpression and RNA interference (RNAi) approaches in alfalfa (Medicago sativa L.) under drought and aluminum (Al) stresses. MsLEA1 was highly expressed in leaves and localized in chloroplasts. Overexpressing MsLEA1 increased alfalfa tolerance to drought and Al stresses, but downregulating MsLEA1 decreased the tolerance. We observed a larger stomatal aperture and a lower water use efficiency in MsLEA1 RNAi lines compared with wild-type plants under drought stress. Photosynthetic rate, Rubisco activity, and superoxide dismutase (SOD) activity increased or decreased in MsLEA1-OE or MsLEA1-RNAi lines, respectively, under drought and Al stress. Copper/zinc SOD (Cu/Zn-SOD), iron SOD (Fe-SOD), and Rubisco large subunit proteins (Ms1770) were identified as binding partners of MsLEA1, which protected chloroplast structure and function under drought and Al stress. These results indicate that MsLEA1 recruits and protects its target proteins (SOD and Ms1770) and increases alfalfa tolerance against drought and Al stresses.

Transcription factor DcbZIPs regulate secondary metabolism in Dendrobium catenatum during cold stress.

Cold stress seriously affects plant development and secondary metabolism. The basic region/leucine zipper (bZIP) is one of the largest transcription factor (TFs) family and widely involved in plant cold stress response. However, the function of bZIP in Dendrobium catenatum has not been well-documented. Cold inhibited the growth of D. catenatum and increased total polysaccharide and alkaloid contents in stems. Here, 62 DcbZIP genes were identified in D. catenatum, which were divided into 13 subfamilies. Among them, 58 DcbZIPs responded to cold stress, which were selected based on the transcriptome database produced from cold-treated D. catenatum seedlings. Specifically, the expression of DcbZIP3/6/28 was highly induced by cold treatment in leaves or stems. Gene sequence analysis indicated that DcbZIP3/6/28 contains the bZIP conserved domain and is localized to the cell nucleus. Co-expression networks showed that DcbZIP6 was significantly negatively correlated with PAL2 (palmitoyl-CoA), which is involved in flavonoid metabolism. Moreover, DcbZIP28 has significant negative correlations with various metabolism-related genes in the polysaccharide metabolic pathway, including PFKA1 (6-phosphofructokinase), ALDO2 (aldose-6-phosphate reductase) and SCRK5 (fructokinase). These results implied that DcbZIP6 or DcbZIP28 are mainly involved in flavonoid or polysaccharide metabolism. Overall, these findings provide new insights into the roles of the DcbZIP gene family in secondary metabolism in D. catenatum under cold stress.

MsMYB741 is involved in alfalfa resistance to aluminum stress by regulating flavonoid biosynthesis.

Aluminum (Al) toxicity severely restricts plant growth in acidic soils (pH < 5.0). In this study, an R2R3-MYB transcription factor (TF) gene, MsMYB741, was cloned from alfalfa. Its function and gene regulatory pathways were studied via overexpression and RNA interference of MsMYB741 in alfalfa seedlings. Results showed that root elongation increased as a result of MsMYB741 overexpression (MsMYB741-OE) and decreased with MsMYB741 RNA interference (MsMYB741-RNAi) in alfalfa seedlings compared with the wild-type under Al stress. These were attributed to the reduced Al content in MsMYB741-OE lines, and increased Al content in MsMYB741-RNAi lines. MsMYB741 positively activated the expression of phenylalanine ammonia-lyase 1 (MsPAL1) and chalcone isomerase (MsCHI) by binding to MYB and ABRE elements in their promoters, respectively, which directly affected flavonoid accumulation in roots and secretion from root tips in plants under Al stress, eventually affecting Al accumulation in alfalfa. Additionally, MsABF2 TF directly activated the expression of MsMYB741 by binding to the ABRE element in its promoter. Taken together, our results indicate that MsMYB741 transcriptionally activates MsPAL1 and MsCHI expression to increase flavonoid accumulation in roots and secretion from root tips, leading to increased resistance of alfalfa to Al stress.

Dehydrin MsDHN1 improves aluminum tolerance of alfalfa (Medicago sativa L.) by affecting oxalate exudation from root tips.

A SK3 -type dehydrin MsDHN1 was cloned from alfalfa (Medicago sativa L.). Its function and gene regulatory pathways were studied via overexpression and suppression of MsDHN1 in alfalfa seedlings or hairy roots. The results showed that MsDHN1 is a typical intrinsically disordered protein that exists in the form of monomers and homodimers in alfalfa. The plant growth rates increased as a result of MsDHN1 overexpression (MsDHN1-OE) and decreased upon MsDHN1 suppression (MsDHN1-RNAi) in seedlings or hairy roots of alfalfa compared with the wild-type or the vector line under Al stress. MsDHN1 interacting with aquaporin (AQP) MsPIP2;1 and MsTIP1;1 positively affected oxalate secretion from root tips and Al accumulation in root tips. MsABF2 was proven to be an upstream transcription factor of MsDHN1 and activated MsDHN1 expression by binding to the ABRE element of the MsDHN1 promoter. The transcriptional regulation of MsABF2 on MsDHN1 was dependent on the abscisic acid signaling pathway. These results indicate that MsDHN1 can increase alfalfa tolerance to Al stress via increasing oxalate secretion from root tips, which may involve in the interaction of MsDHN1 with two AQP.

Analysis of the Function of the Alfalfa Mslea-D34 Gene in Abiotic Stress Responses and Flowering Time.

A novel late embryogenesis abundant (LEA) gene, MsLEA-D34, was cloned from alfalfa (Medicago sativa L.). Its function and gene regulatory pathways were studied via overexpression (OE) and RNA interference (RNAi) of the gene in Arabidopsis and in hairy roots of alfalfa, as well as via analyzing key genes related to MsLEA-D34 during developmental phases in alfalfa. The results showed that MsLEA-D34 was a typical intrinsically disordered protein with a high capability for protein protection. Overexpression of MsLEA-D34 increased plant tolerance to osmotic and salt stresses, and caused Arabidopsis early flowering under drought and well-watered conditions. Overexpressing MsLEA-D34 induced up-regulation of FLOWERING LOCUS T (FT) and GIGANTEA (GI) at the flowering phase of Arabidopsis and hairy roots of alfalfa, but only FT was down-regulated in MsLEA-D34-RNAi lines. A positive effect of MsLEA-D34 on FT accumulation was demonstrated in alfalfa hairy roots. An ABA-responsive element (ABRE)-binding transcription factor (MsABF2), a novel transcription factor cloned from alfalfa, directly bound to the RY element in the MsLEA-D34 promoter and activated MsLEA-D34 expression. The above results indicate that MsLEA-D34 can regulate abiotic stress response in plants and influence flowering time of Arabidopsis.

Characterization of Dehydrin protein, CdDHN4-L and CdDHN4-S, and their differential protective roles against abiotic stress in vitro.

BACKGROUND: Dehydrins play positive roles in regulating plant abiotic stress responses. The objective of this study was to characterize two dehydrin genes, CdDHN4-L and CdDHN4-S, generated by alternative splicing of CdDHN4 in bermudagrass. RESULTS: Overexpression of CdDHN4-L with φ-segment and CdDHN4-S lacking of φ-segment in Arabidopsis significantly increased tolerance against abiotic stresses. The growth phenotype of Arabidopsis exposed to NaCl at 100 mM was better in plants overexpressing CdDHN4-L than those overexpressing CdDHN4-S, as well as better in E.coli cells overexpressing CdDHN4-L than those overexpressing CdDHN4-S in 300 and 400 mM NaCl, and under extreme temperature conditions at - 20 °C and 50 °C. The CdDHN4-L had higher disordered characterization on structures than CdDHN4-S at temperatures from 10 to 90 °C. The recovery activities of lactic dehydrogenase (LDH) and alcohol dehydrogenase (ADH) in presence of CdDHN4-L and CdDHN4-S were higher than that of LDH and ADH alone under freeze-thaw damage and heat. Protein-binding and bimolecular fluorescence complementation showed that both proteins could bind to proteins with positive isoelectric point via electrostatic forces. CONCLUSIONS: These results indicate that CdDHN4-L has higher protective ability against abiotic stresses due to its higher flexible unfolded structure and thermostability in comparison with CdDHN4-S. These provided direct evidence of the function of the φ-segment in dehydrins for protecting plants against abiotic stress and to show the electrostatic interaction between dehydrins and client proteins.

Rapid Prediction of Adulteration Content in Atractylodis rhizoma Based on Data and Image Features Fusions from Near-Infrared Spectroscopy and Hyperspectral Imaging Techniques.

Atractylodis rhizoma (AR) is an herb and food source with great economic, medicinal, and ecological value. Atractylodes chinensis (DC.) Koidz. (AC) and Atractylodes lancea (Thunb.) DC. (AL) are its two botanical sources. The commercial fraud of AR adulterated with Atractylodes japonica Koidz. ex Kitam (AJ) frequently occurs in pursuit of higher profit. To quickly determine the content of adulteration in AC and AL powder, two spectroscopic techniques, near-infrared spectroscopy (NIRS) and hyperspectral imaging (HSI), were introduced. The partial least squares regression (PLSR) algorithm was selected for predictive modeling of AR adulteration levels. Preprocessing and feature variable extraction were used to optimize the prediction model. Then data and image feature fusions were developed to obtain the best predictive model. The results showed that if only single-spectral techniques were considered, NIRS was more suitable for both tasks than HSI techniques. In addition, by comparing the models built after the data fusion of NIRS and HSI with those built by the single spectrum, we found that the mid-level fusion strategy obtained the best models in both tasks. On this basis, combined with the color-texture features, the prediction ability of the model was further optimized. Among them, for the adulteration level prediction task of AC, the best strategy was combining MLF data (at CARS level) and color-texture features (C-TF), at which time the R2T, RMSET, R2P, and RMSEP were 99.85%, 1.25%, 98.61%, and 5.06%, respectively. For AL, the best approach was combining MLF data (at SPA level) and C-TF, with the highest R2T (99.92%) and R2P (99.00%), as well as the lowest RMSET (1.16%) and RMSEP (2.16%). Therefore, combining data and image features from NIRS and HSI is a potential strategy to predict the adulteration content quickly, non-destructively, and accurately.

Auxin Is Involved in Magnesium-Mediated Photoprotection in Photosystems of Alfalfa Seedlings Under Aluminum Stress.

The objective of this study was to investigate the effects of Mg and IAA on the photosystems of Al-stressed alfalfa (Medicago sativa L.). Alfalfa seedlings with or without apical buds were exposed to solutions fully mixed with 0 or 100 µM AlCl3 and 0 or 50 µM MgCl2 followed by foliar spray with water or IAA. Results from seedlings with apical buds showed that application of Mg and IAA either alone or combine greatly alleviated the Al-induced damage on photosystems. The values of photosynthetic rate (Pn), effective quantum yields [Y(I) and Y(II)] and electron transfer rates (ETRI and ETRII), proton motive force (pmf), cyclic electron flow (CEF), proton efflux rate (gH +), and activities of ATP synthase and PM H+-ATPase significantly increased, and proton gradient (ΔpH pmf ) between lumen and stroma decreased under Al stress. After removing apical buds of seedlings, the Y(I), Y(II), ETRI, ETRII, pmf, and gH + under exogenous spraying IAA significantly increased, and ΔpH pmf significantly decreased in Mg addition than Al treatment alone, but they were no significant difference under none spraying IAA. The interaction of Mg and IAA directly increased quantum yields and electron transfer rates, and decreased O2 - accumulation in Al-stressed seedlings with or without apical buds. These results suggest that IAA involves in Mg alleviation of Al-induced photosystem damage via increasing pmf and PM H+-ATPase activity, and decreasing ΔpH pmf .

Protective functions of alternative splicing transcripts (CdDHN4-L and CdDHN4-S) of CdDHN4 from bermudagrass under multiple abiotic stresses.

Dehydrins (DHNs) play critical roles in plant adaptation to abiotic stresses. The objective of this study was to characterize DHNs in bermudagrass (Cynodon spp.). CdDHN4 gene was cloned from bermudagrass 'Tifway'. Two CdDHN4 transcripts were detected due to alternative splicing (the nonspliced CdDHN4-L and the spliced CdDHN4-S) and both the CdDHN4-S and CdDHN4-L proteins are YSK2-type DHNs, the Φ-segment is present in CdDHN4-L and absent in CdDHN4-S. Transgenic Arabidopsis thaliana expressing CdDHN4-L or CdDHN4-S exhibited improved tolerance to salt, osmotic, low temperature and drought stress compared to the wild type (WT). The two transgenic lines did not differ in salt or drought tolerance, while plants expressing CdDHN4-S grew better under osmotic stress than those expressing CdDHN4-L. Both transgenic lines exhibited reduced content of malondialdehyde (MDA) and reactive oxygen species (ROS); and higher antioxidant enzymatic activities than the wild type plants under salt or drought stress. CdDHN4-S exhibited a higher ROS-scavenging capacity than CdDHN4-L.

Protective functions of alternative splicing transcripts (CdDHN4-L and CdDHN4-S) of CdDHN4 from bermudagrass under multiple abiotic stresses.

Dehydrins (DHNs) play critical roles in plant adaptation to abiotic stresses. The objective of this study was to characterize DHNs in bermudagrass (Cynodon spp.). CdDHN4 gene was cloned from bermudagrass 'Tifway'. Two CdDHN4 transcripts were detected due to alternative splicing (the nonspliced CdDHN4-L and the spliced CdDHN4-S) and both the CdDHN4-S and CdDHN4-L proteins are YSK2-type DHNs, the Φ-segment is present in CdDHN4-L and absent in CdDHN4-S. Transgenic Arabidopsis thaliana expressing CdDHN4-L or CdDHN4-S exhibited improved tolerance to salt, osmotic, low temperature and drought stress compared to the wild type (WT). The two transgenic lines did not differ in salt or drought tolerance, while plants expressing CdDHN4-S grew better under osmotic stress than those expressing CdDHN4-L. Both transgenic lines exhibited reduced content of malondialdehyde (MDA) and reactive oxygen species (ROS); and higher antioxidant enzymatic activities than the wild type plants under salt or drought stress. CdDHN4-S exhibited a higher ROS-scavenging capacity than CdDHN4-L.

Expression of CdDHN4, a Novel YSK2-Type Dehydrin Gene from Bermudagrass, Responses to Drought Stress through the ABA-Dependent Signal Pathway.

Dehydrin improves plant resistance to many abiotic stresses. In this study, the expression profiles of a dehydrin gene, CdDHN4, were estimated under various stresses and abscisic acid (ABA) treatments in two bermudagrasses (Cynodon dactylon L.): Tifway (drought-tolerant) and C299 (drought-sensitive). The expression of CdDHN4 was up-regulated by high temperatures, low temperatures, drought, salt and ABA. The sensitivity of CdDHN4 to ABA and the expression of CdDHN4 under drought conditions were higher in Tifway than in C299. A 1239-bp fragment, CdDHN4-P, the partial upstream sequence of the CdDHN4 gene, was cloned by genomic walking from Tifway. Bioinformatic analysis showed that the CdDHN4-P sequence possessed features typical of a plant promoter and contained many typical cis elements, including a transcription initiation site, a TATA-box, an ABRE, an MBS, a MYC, an LTRE, a TATC-box and a GT1-motif. Transient expression in tobacco leaves demonstrated that the promoter CdDHN4-P can be activated by ABA, drought and cold. These results indicate that CdDHN4 is regulated by an ABA-dependent signal pathway and that the high sensitivity of CdDHN4 to ABA might be an important mechanism enhancing the drought tolerance of bermudagrass.

Gene Expression Analysis of Alfalfa Seedlings Response to Acid-Aluminum.

Acid-Aluminum (Al) is toxic to plants and greatly affects crop production worldwide. To understand the responses of plants to acid soils and Aluminum toxicity, we examined global gene expression using microarray data in alfalfa seedlings with the treatment of acid-Aluminum. 3,926 genes that were identified significantly up- or downregulated in response to Al3+ ions with pH 4.5 treatment, 66.33% of which were found in roots. Their functional categories were mainly involved with phytohormone regulation, reactive oxygen species, and transporters. Both gene ontology (GO) enrichment and KEGG analysis indicated that phenylpropanoid biosynthesis, phenylalanine metabolism, and flavonoid biosynthesis played a critical role on defense to Aluminum stress in alfalfa. In addition, we found that transcription factors such as the MYB and WRKY family proteins may be also involved in the regulation of reactive oxygen species reactions and flavonoid biosynthesis. Thus, the finding of global gene expression profile provided insights into the mechanisms of plant defense to acid-Al stress in alfalfa. Understanding the key regulatory genes and pathways would be advantageous for improving crop production not only in alfalfa but also in other crops under acid-Aluminum stress.

Increase phosphorus availability from the use of alfalfa (Medicago sativa L) green manure in rice (Oryza sativa L.) agroecosystem.

Alfalfa is a good green manure source, but its effect on rice growth has not been fully elucidated. Two green manure species, alfalfa and broad bean (Vicia faba L.), and two N fertilizer levels, alone or combination, were applied to a rice field. The results indicated that alfalfa had more pronounced effects on increasing soil labile phosphorus (P) fractions (including NaHCO3-Pi, NaOH-Pi), P uptake and soil enzyme activities (dehydrogenase, urease, acid phosphatase and ß-glucosidase) than broad bean and N fertilizer. The transformation of NaHCO3-Po to labile P regulated by alfalfa played a significant direct and indirect effect on grain yield. Although a much lower N input from alfalfa addition, a similar grain yield with N fertilizer treatment was achieved, and the integration of alfalfa with N fertilizer produced the highest grain yield and P availability, which was associated with the highest urease, acid phosphatase and ß-glucosidase activity in soil. These results indicate that alfalfa green manure had a great ability of increasing grain yield through enhancing P availability in rice paddy, which could give us a way to reduce N fertilizer application by enhancing P availability.