The Use of Gene Modification and Advanced Molecular Structure Analyses towards Improving Alfalfa Forage

MsTFL1A delays flowering and regulates shoot architecture and root development in Medicago sativa

KEY MESSAGE

MsTFL1A is an important gene involved in flowering repression in alfalfa (Medicago sativa) which conditions not only above-ground plant shoot architecture but also root development and growth. Delayed flowering is an important trait for forage species, as it allows harvesting of high-quality forage for a longer time before nutritional values decline due to plant architecture changes related to flowering onset. Despite the relevance of delayed flowering, this trait has not yet been thoroughly exploited in alfalfa. This is mainly due to its complex genetics, sensitivity to inbreeding and to the fact that delayed flowering would be only advantageous if it allowed increased forage quality without compromising seed production. To develop new delayed-flowering varieties, we have characterized the three TERMINAL FLOWERING 1 (TFL1) family of genes in alfalfa: MsTFL1A, MsTFL1B and MsTFL1C. Constitutive expression of MsTFL1A in Arabidopsis caused late flowering and changes in inflorescence architecture, indicating that MsTFL1A is the ortholog of Arabidopsis TFL1. Overexpression of MsTFL1A in alfalfa consistently led to delayed flowering in both controlled and natural field conditions, coupled to an increase in leaf/stem ratio, a common indicator of forage quality. Additionally, overexpression of MsTFL1A reduced root development, reinforcing the role of MsTFL1A not only as a flowering repressor but also as a regulator of root development.We conclude that the precise manipulation of MsTFL1A gene expression may represent a powerful tool to improve alfalfa forage quality.

Effects of Selenium on the Lignin Deposition Pattern and Stem Mechanical Properties of Alfalfa (Medicago sativa L.)

Lignin provides structural support to plants; however, it reduces their utilization rate. According to our previous studies, selenium (Se) reduces lignin accumulation in alfalfa, but the specific mechanism involved remains unclear. Therefore, at the seedling stage, four root irrigation treatments using 2.5, 50, and 5 μmol/L sodium selenite (S-RI), selenomethionine (SS-RI), Se nanoparticles (SSS-RI), and deionized water (CK-RI) were performed. At the branching stage, four treatments of foliar spraying with the three Se fertilizers described above at a concentration of 0.5 mmol/L (S-FS, SS-FS, and SSS-FS) and deionized water (CK-FS) were administered. The results revealed that all Se treatments chiefly reduced the level of deposition of syringyl (S) lignin in the first internode of alfalfa stems. SS-FS and SSS-FS treatments mainly reduced the deposition of S and guaiacyl (G) lignins in the sixth internode of alfalfa stems, respectively, while S-FS treatment only slightly reduced the deposition of G lignin. S, SS, and SSS-RI treatments reduced the level of deposition of S and G lignins in the sixth internode of alfalfa stems. Se application increased plant height, stem diameter, epidermis (cortex) thickness, primary xylem vessel number (diameter), and pith diameter of alfalfa but decreased primary xylem area and pith parenchyma cell wall thickness of the first internode, and SS(SSS)-FS treatment reduced the mechanical strength of alfalfa stems. Therefore, Se application could decrease lignin accumulation by regulating the organizational structure parameters of alfalfa stems and the deposition pattern of the lignin monomers.

Transcriptomic Analysis of Self-Incompatibility in Alfalfa

Alfalfa (Medicago sativa L.) is an important forage crop worldwide, but molecular genetics and breeding research in this species are hindered by its self-incompatibility (SI). Although the mechanisms underlying SI have been extensively studied in other plant families, SI in legumes, including alfalfa, remains poorly understood. Here, we determined that self-pollinated pollen tubes could germinate on the stigma of alfalfa, grow through the style, and reach the ovarian cavity, but the ovules collapsed ~48 h after self-pollination. A transcriptomic analysis of dissected pistils 24 h after self-pollination identified 941 differently expressed genes (DEGs), including 784 upregulated and 157 downregulated genes. A gene ontology (GO) analysis showed that the DEGs were highly enriched in functions associated with the regulation of pollen tube growth and pollen germination. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that pentose and glucuronate interconversion, plant hormone signal transduction, the spliceosome, and ribosomes might play important roles in SI. Our co-expression analysis showed that F-box proteins, serine/threonine protein kinases, calcium-dependent protein kinases (CDPKs), bHLHs, bZIPs, and MYB-related family proteins were likely involved in the SI response. Our study provides a catalog of candidate genes for further study to understand SI in alfalfa and related legumes.

Ethnobotanical study of traditional forage plants in the Gansu-Ningxia-Inner Mongolia junction zone: conservation and sustainable utilization for animal husbandry

INTRODUCTION

This study aims to safeguard the ethnobotanical knowledge pertaining to traditional forage plants within the ethnically diverse Gansu-Ningxia-Inner Mongolia junction zone. It seeks to establish a foundation for the sustainable utilization of these traditional resources for animal husbandry.

METHODS

A combination of literature research, village interviews, participatory observation, and ethnobotanical quantitative evaluation methods was employed to investigate and study the traditional knowledge of wild forage plants used by local residents in the study area.

RESULTS

Local residents provided information on 73 forage plants, which were identified as 116 distinct wild forage plant species. These plants belong to 22 families and play an active role in the lives of the local inhabitants. Notably, the families Poaceae, Fabaceae, and Asteraceae are prominent, comprising the most abundant and widely utilized wild forage plants. Bing Cao (collectively referring to plants of the Agropyron, Leymus, and Psammochloa), Suo Cao (collectively referring to plants of the genus Stipa), and Ku Cai (encompassing Lactuca tatarica (L.) C.A.Mey. and Ixeris polycephala Cass.) emerge as the most representative and vital wild forage plants for animal husbandry. Additionally, plants within the Astragalus (referred to collectively as NiaoZi by local residents) in the Fabaceae family, as well as plants from the Amaranthaceae family, exhibit notable significance.

CONCLUSION

Animal husbandry assumes a pivotal role in the local agricultural economy, and the 116 wild forage plants investigated hold substantial importance in its development. Among these, 59 and 103 plant resources display high developmental potential, making them prospective candidates for high-quality cultivated forage grasses. Additionally, extensive grazing practices have resulted in significant ecological degradation within this already fragile ecosystem. The cultivation of forage grasses and the practice of pen-based animal husbandry may emerge as crucial strategies for sustainable development in this area.

Using vibrational molecular spectroscopy to reveal carbohydrate molecular structure properties of faba bean partitions and faba bean silage before and after rumen incubation in relation to nutrient availability and supply to dairy cattle

To our knowledge, there is limited study on the relationship between the molecular structure of feed and nutrient availability in the ruminant system. The objective of this study is to use advanced vibrational molecular spectroscopy (attenuated total reflection [ATR]-Fourier transform infrared [FT/IR]) to reveal carbohydrate molecular structure properties of faba bean partitions (stem, leaf, whole pods [WP], and whole plant) and faba bean silage before and after rumen incubation in relation to nutrient availability and supply to dairy cattle. The study included the correlation between carbohydrate-related spectral profiles and chemical profiles, feed energy values, Cornell Net Carbohydrate and Protein System carbohydrate fractions, and rumen degradation parameters of faba bean samples (whole crop, stem, leaf, WP, and silage) before and after rumen incubation. FTIR spectra of faba bean sample before and after 12 and 24 h rumen incubations were collected with JASCO FT/IR-4200 with ATR at mid-IR range (ca. 4000-700 cm^-1 ) with 128 scans and at 4 cm^-1 resolution. The univariate molecular spectral analysis was carried out using OMNIC software. The results show that ATR-FT/IR spectroscopic technique could detect the change of microbial digestion to carbohydrate-related molecular structure. The spectral parameters of feed rumen incubation residues had a stronger correlation with less degradable carbohydrate fractions (neutral detergent fiber, acid detergent fiber, acid detergent lignin, hemicellulose, and cellulose) while spectral profiles of original faba samples had a stronger correlation with easily degradable carbohydrate fractions (starch). In conclusion, rumen degradation of carbohydrate contents can be reflected in the change of its molecular spectral profiles. The study shows that vibrational molecular spectroscopy (ATR-FT/IR) shows high potential as a fast analytical tool to evaluate and predict nutrient supply in the ruminant system.

Combination of Medium- and High-Pressure Liquid Chromatography for Isolation of L-tryptophan (Q-marker) from Medicago sativa Extract

Medicago sativa (alfalfa) is a widely used animal feed. However, its quality has been difficult to control due to the lack of appropriate marker compounds. Therefore, it is very necessary to select an appropriate quality marker (Q-marker) to control its quality. In this study, medium-pressure liquid chromatography and high-pressure liquid chromatography were employed to effectively prepare the separation of the Q-marker (L-tryptophan) from Medicago sativa. Firstly, using MCI GEL® CHP20P as the stationary phase, 2.5 g of the target fraction Fr3 was enriched from crude Medicago sativa extract (2.9 kg) by medium-pressure liquid chromatography. Secondly, Sephadex LH-20 was used to further separate Fr3 fractions, and the Fr34 fraction (358.3 mg) was enriched after 14 repetitions. Lastly, using the ReproSil-Pur C18 AQ preparative column, 63.4 mg of L-tryptophan was obtained by high-pressure liquid chromatography, and the purity was above 95%. The results showed that medium-pressure liquid chromatography (MCI GEL® CHP20P and Sephadex LH-20) combined with high-pressure liquid chromatography (ReproSil-Pur C18 AQ) could be used to effectively prepare the Q-marker from natural products with satisfactory purity.

Mechanism of pod shattering in the forage legume Medicago ruthenica

Pod shattering is a seed dispersal strategy and an important agronomical trait in domesticated crops. The relationship between pod shattering and pod morphology in the genus Medicago is well known; however, the detailed mechanism underlying pod dehiscence in Medicago ruthenica, a perennial legume used for forage production, is unknown. Here, the pod ventral sutures of shatter-resistant and shatter-susceptible M. ruthenica genotypes were examined at 8, 12, 16, and 20 d after flowering. The mechanism of pod shattering was analyzed through microscopic observations, polygalacturonase (PG) and cellulase (CE) activity analyses, and RNA-sequencing (RNA-Seq), and the results were verified via reverse transcriptase-quantitative polymerase chain reaction. Pod shattering at the ventral suture in M. ruthenica occurs via a combination of two mechanisms: degradation of the middle lamella at the abscission layers (ALs) and detachment of lignified cells on either side of the ALs triggered by physical forces. Increased PG and CE activities in the pod ventral suture are essential for AL cell-autolysis in the shatter-susceptible genotype. RNA-Seq revealed that 11 genes encoding PG and CE were highly expressed in the ventral sutures of the shatter-susceptible genotype. The expression levels of auxin biosynthesis-related genes decreased in the AL cells and they were negatively associated with pod dehiscence. These results enhance our understanding of the pod shattering mechanism not only in M. ruthenica but also in other leguminous plants.

Controlling flowering of Medicago sativa (alfalfa) by inducing dominant mutations

Breeding plants with polyploid genomes is challenging because functional redundancy hampers the identification of loss-of-function mutants. Medicago sativa is tetraploid and obligate outcrossing, which together with inbreeding depression complicates traditional breeding approaches in obtaining plants with a stable growth habit. Inducing dominant mutations would provide an alternative strategy to introduce domestication traits in plants with high gene redundancy. Here we describe two complementary strategies to induce dominant mutations in the M. sativa genome and how they can be relevant in the control of flowering time. First, we outline a genome-engineering strategy that harnesses the use of microProteins as developmental regulators. MicroProteins are small proteins that appeared during genome evolution from genes encoding larger proteins. Genome-engineering allows us to retrace evolution and create microProtein-coding genes de novo. Second, we provide an inventory of genes regulated by microRNAs that control plant development. Making respective gene transcripts microRNA-resistant by inducing point mutations can uncouple microRNA regulation. Finally, we investigated the recently published genomes of M. sativa and provide an inventory of breeding targets, some of which, when mutated, are likely to result in dominant traits.

Proteomic analysis reveals responsive mechanisms for saline-alkali stress in alfalfa

Saline-alkali stress is a major abiotic stress that limits plant growth, yield, and geographical distribution. Alfalfa is a perennial legume with the largest planting area in the world because of its high protein content, good palatability, and long utilization life. However, saline-alkali stress seriously affects alfalfa yield and quality. To better understand the saline-alkali stress response mechanisms of alfalfa, an isobaric tags proteomics method was used to compare and analyse alfalfa under saline-alkali stress for 0, 1, and 7 days, and 126 (1 vs. 0 days) and 1869 (7 vs. 0 days) differentially abundant proteins (DAPs) were found. Through integrative analysis with differentially expressed genes (DEGs), we found correlated DEGs-DAPs of RNA and protein with similar expression trends at the mRNA and protein levels; these were mainly involved in ABA and Ca²⁺ signal pathways, regulation of photosynthesis, ROS scavenging, secondary metabolism, and transcription factors (TFs) related to saline-alkali stress. Some genes not exhibiting such trends may have been regulated post-transcriptionally. Furthermore, through transgenic experiments, MsFTL was found to significantly improve the saline-alkali tolerance of plants. Overall, our findings provide important clues for understanding the molecular mechanisms underlying the response of alfalfa to saline-alkali stress.

Overexpression of alfalfa SIMK promotes root hair growth, nodule clustering and shoot biomass production

Nitrogen-fixing rhizobia and legumes have developed complex mutualistic mechanism that allows to convert atmospheric nitrogen into ammonia. Signalling by mitogen-activated protein kinases (MAPKs) seems to be involved in this symbiotic interaction. Previously, we reported that stress-induced MAPK (SIMK) shows predominantly nuclear localization in alfalfa root epidermal cells. Nevertheless, SIMK is activated and relocalized to the tips of growing root hairs during their development. SIMK kinase (SIMKK) is a well-known upstream activator of SIMK. Here, we characterized production parameters of transgenic alfalfa plants with genetically manipulated SIMK after infection with Sinorhizobium meliloti. SIMKK RNAi lines, causing strong downregulation of both SIMKK and SIMK, showed reduced root hair growth and lower capacity to form infection threads and nodules. In contrast, constitutive overexpression of GFP-tagged SIMK promoted root hair growth as well as infection thread and nodule clustering. Moreover, SIMKK and SIMK downregulation led to decrease, while overexpression of GFP-tagged SIMK led to increase of biomass in above-ground part of plants. These data suggest that genetic manipulations causing downregulation or overexpression of SIMK affect root hair, nodule and shoot formation patterns in alfalfa, and point to the new biotechnological potential of this MAPK.

Synchrotron-radiation sourced SR-IMS molecular spectroscopy to explore impact of silencing TT8 and HB12 genes in alfalfa leaves on the molecular structure and chemical mapping

Advanced synchrotron-based vibrational molecular spectroscopy (SR-IMS) has been developed to image molecular chemistry in biological tissues within cellular and subcellular dimension. However, it is seldomly used in gene-transformation and gene-silencing study. The objectives of this study were to apply synchrotron-based vibrational molecular spectroscopy (SR-IMS) to determine the molecular structural changes and chemical mapping of alfalfa leaves induced by silencing of TT8 and HB12 genes in alfalfa in comparison with wild type of alfalfa. Five alfalfa leaves from each alfalfa genotype were selected for FTIR spectra collection and chemical mapping with synchrotron-based FTIR microspectroscopy (SR-IMS). Peak heights and areas of empirical regions were analyzed, and peak areas of previous regions were mapped for each sample using OMNIC 7.3. Results showed that transformed alfalfa had higher peak height and area of carbonyl CO (CCO), compared with wild type (WT). Chemical groups maps for carbohydrate, amide and lipid-related regions were successfully obtained. HB12-silenced (HB12i) had higher carbohydrate intensity both in the mesophyll and epidermises, whereas TT8-silenced (TT8i) and WT only had higher carbohydrate spectral peak intensity in epidermises. In addition, HB12i had higher CCO intensity and lower lignin intensity compared with TT8i and WT. All alfalfa genotypes had higher intensity of amide and asymmetric and symmetric CH2 and CH3 (ASCC) area in mesophylls. In conclusion, silencing of HB12 and TT8 genes in alfalfa both increased CCO profiles of alfalfa leaves, while silencing of HB12 had more impacts on chemical localization in alfalfa leaves.

Effect of replacing soybean meal with marula nut meal on rumen dry matter and crude protein degradability

In situ rumen degradability of dry matter (DM) and crude protein (CP) in ruminant diets composed of graded inclusion levels of marula nut meal (MNM) as a protein source to replace soybean meal were evaluated. The five diets denoted as diet 1 (0.0 g kg^-1 MNM: control), diet 2 (45.5 g kg^-1 MNM), diet 3 (91.7 g kg^-1 MNM), diet 4 (138.4 g kg^-1 MNM), and diet 5 (185.9 g kg^-1 MNM) were tested. Three cannulated mid-lactating Holstein cows were used to incubate triplicate subsamples of each diet for 2, 4, 8, 16, 24, and 48 h in polyester bags. The soluble fractions of DM and CP increased (P < 0.05) with increasing levels of MNM (138.4-185.9 g kg^-1 MNM). However, the insoluble but degradable fractions of DM and CP increased (P < 0.05) with decreasing levels of MNM (45.5-0.0 g kg^-1 and 91.7-0.0 g kg^-1 MNM, respectively). While the degradation rate of fraction and the effective degradability of DM increased (P < 0.05) with decreasing levels of MNM (91.7-0.0 g kg^-1), those of CP increased with increasing levels of MNM (138.4-185.9 g kg^-1 MNM) in the diet. These results suggest that dietary inclusion of MNM up to 91.7 g kg^-1 in ruminant diets can provide undegradable protein to be absorbed in the small intestines and used for metabolic function, while an inclusion of up to 185.9 g kg^-1 can be degraded in the rumen for microbial protein synthesis.

Hay Yield and Water Use Efficiency of Alfalfa under Different Irrigation and Fungicide Regimes in a Semiarid Climate

Alfalfa is one of the most nutritive and high-yielding forage legumes planted in rotation with cereal crops across the United States. Under semiarid and arid climates with limited water resources, sustainable management of the available resources is required. The objective of this study was to investigate the effect of different irrigation regimes and fungicide applications on alfalfa in the high desert region of the Colorado Plateau of the U.S. Field experiments were conducted during the 2012–2014 period. Alfalfa was planted in fall 2012, uniformly irrigated for crop establishment and subjected to seven different irrigation regimes after the first cut in spring 2013. Alfalfa was treated by fungicide application and was harvested at 10% blooming. The maximum amounts of applied water were 350, 300, 208, and 312 mm, respectively, during the first, second, third, and fourth regrowth cycles in 2013, and 373, 282, 198, and 246 mm in 2014 for the respective regrowth cycles in 2014; the seasonal applied irrigation amount varied from 711 to 1171 mm in 2013 and from 328 to 1100 mm in 2014. The results showed non-significant effect of fungicide application on the forage yield. Alfalfa forage yield was significantly affected by the irrigation regimes and showed a third order polynomial relationship with the applied irrigation amounts during each regrowth cycle and on seasonal scale. Forage yield decreased from the first cut to the fourth cut and the annual forage varied from 10.6 to 25.7 Mg/ha for the treated alfalfa and from 11.5 to 25.6 Mg/ha for the non-treated alfalfa. Forage yield at each cut accounted for 39.6, 24.2, 17.6, and 18.6% of the 2013 season forage yield and 31.4, 23.8, 21.6, and 23.2% of the 2014 season forage yield, for the first, second, third, and fourth cut, respectively. Alfalfa water use efficiency varied from 0.06 to 3.3 kg/m3. The relationships developed in this study could be used by forage growers, crop consultants, and project managers for decision making and planning to improve the productivity of water under the semiarid and arid climate of New Mexico and the surrounding regions.

Improvement of alfalfa forage quality and management through the down-regulation of MsFTa1

Alfalfa (Medicago sativa L.) is one of the most important forage crops worldwide. As a perennial, alfalfa is cut several times each year. Farmers face a dilemma: if cut earlier, forage nutritive value is much higher but regrowth is affected and the longevity of the stand is severely compromised. On the other hand, if alfalfa is cut later at full flower, stands persist longer and more biomass may be harvested, but the nutritive value diminishes. Alfalfa is a strict long-day plant. We reasoned that by manipulating the response to photoperiod, we could delay flowering to improve forage quality and widen each harvesting window, facilitating management. With this aim, we functionally characterized the FLOWERING LOCUS T family of genes, represented by five members: MsFTa1, MsFTa2, MsFTb1, MsFTb2 and MsFTc. The expression of MsFTa1 correlated with photoperiodic flowering and its down-regulation led to severe delayed flowering. Altogether, with late flowering, low expression of MsFTa1 led to changes in plant architecture resulting in increased leaf to stem biomass ratios and forage digestibility. By manipulating photoperiodic flowering, we were able to improve the quality of alfalfa forage and management, which may allow farmers to cut alfalfa of high nutritive value without compromising stand persistence.

Silencing TT8 and HB12 Decreased Protein Degradation and Digestion, Microbial Synthesis, and Metabolic Protein in Relation to Molecular Structures of Alfalfa (Medicago sativa)

This study aimed to explore the effects of silencing HB12 and TT8 genes on protein utilization characteristics of alfalfa. Ground samples of 11 HB12-silenced (HB12i), 5 TT8-silenced (TT8i) and 4 wild type (WT) were incubated in a Daisy II incubator with N¹⁵ labeled ammonium sulfate for 0, 4, 8, 12, and 24 h. CP degradation and degradational kinetics, microbial nitrogen fractions, and protein metabolic profiles were determined. Moreover, relationships between protein profiles and FTIR spectral parameters were estimated. Results showed that transgenic alfalfa had lower CP degradation, microbial protein, and total available protein compared with WT, especially for HB12i. In addition, CP degradation and protein metabolic profiles were closely correlated with FTIR spectral parameters and thereby could be predicted from spectral parameters. In conclusion, silencing of HB12 and TT8 genes in alfalfa decreased protein degradational and metabolic profiles, which were predictable with FTIR spectral parameters.

Biodegradation Profiles of Proanthocyanidin-Accumulating Alfalfa Plants Coexpressing Lc- bHLH and C1-MYB Transcriptive Flavanoid Regulatory Genes

The utilization of the nutrient potential of alfalfa ( Medicago sativa L.) cannot be maximized because of its rapidly degradable protein content in the rumen, leading to waste and various digestive disorders. This might be alleviated if protein-binding proanthocyanidins are present in aerial parts of alfalfa forage in adequate amounts. The Lc (bHLH) and C1 (MYB) genes of maize are transcription factors known to be collectively involved in the regulation of anthocyanin biosynthetic pathways. The objective of this study was to investigate the effect of Lc and C1 gene transformations on the proanthocyanidin content, nutrient composition, and degradation characteristics of proteins and carbohydrates by comparing the transgenic alfalfa with its parental nontransgenic (NT) alfalfa and commercial AC-Grazeland cultivar. The DNA extracted from transgenic plants was tested for the presence of respective transgenes by amplification with specific primers of respective transgenes using PCR. Both Lc-single and LcC1-double transgenic alfalfa accumulated both monomeric and polymeric proanthocyanidins with total proanthocyanidins ranging from ca. 460 to 770 μg/g of DM. The C1-transgenic alfalfa did not accumulate proanthocyanidins similar to NT alfalfa. The C1 gene increased the NPN content significantly only in C1-single and Lc1C1-double transgenic alfalfa. The LcC1 combination seemed to have a synergic effect on reducing sugar in alfalfa. In contrast, the Lc gene appears to have a negative effect on starch content. The C1 gene tended to lower the PB3 content irrespective of the presence of the Lc gene. Although the cotransformation of Lc and C1 increased the total N/CHO ratio compared to Lc single gene transformation, the total N/CHO ratio of transgenic alfalfa was not significantly different from NT. In conclusion, Lc-bHLH single and LcC1 double gene transformation resulted in the accumulation of proanthocyanidins and affected the chemical profiles in alfalfa, which altered ruminal degradation patterns and impacted the nutrient availability of alfalfa in ruminant livestock systems.

A methodology study on chemical and molecular structure imaging in modified forage leaf tissue with cutting-edge synchrotron-powered technology (SR-IMS) as a potential research tool

To date there is no any study on imaging molecular chemistry and chemical structure of biotech-modified plant tissue on a molecular basis. The objective of this methodology study was to apply a non-invasive and non-destructive synchrotron powered technology - SR-IMS to image molecular chemistry of the modified forage leaf tissue. The infrared molecular vibrational microspectroscopy powered with synchrotron light at Advanced Light Source (ALS, Lawrence Berkeley National Lab, Berkeley, California, Dept. of Energy, USA) were applied. The synchrotron beamline time was arranged by National Synchrotron Light Source (Scientist Dr. Lisa Miller, Brookhaven National Lab, Dept. of Energy, USA). The various molecular functional groups in the forage tissue included CH symmetric and asymmetric regions, amides I and II regions, structure and non-structure CHO regions, carbonyl ester region with peak areas at ca. 3644-3000 cm^-1, ca 3005-2979 cm^-1, ca. 1722-1483 cm^-1, ca. 1488-1412 cm^-1, ca. 1296-1189 cm^-1, and ca. 1194-951 cm^-1. The spectral peak area ratio imaging of chemical functional groups were also studied which included the ratio of peak area under ca. 1722-1483 cm^-1 to peak area under ca. 3005-2979 cm^-1 and the ratio of peak area under ca. 1722-1483 cm^-1 to peak area under ca. 1194-951 cm^-1. The results showed that the advanced synchrotron-based technology - SR-IMS was able to image the forage tissue at an ultra-highly resolution within intact tissue within cellular and subcellular dimension. It revealed the forage tissue in a molecular chemical sense and provided an insight on nutrient properties and their molecular structure as well as chemical features. In conclusion, the synchrotron-radiation SR-IMS is able to image molecular structure of the forage leaf tissue at an ultra-highly resolution. The advanced SR-IMS technique could provide leaf tissue four kinds of information simultaneously: tissue structure, tissue chemistry, tissue nutrients, and tissue environment of forage.

Transcriptome analysis of microRNA156 overexpression alfalfa roots under drought stress

Drought is one of the major abiotic stresses that negatively impact alfalfa growth and productivity. The role of microRNA156 (miR156) in drought has been demonstrated in plants. To date, there are no published studies investigating the role of miR156 in regulating global gene expression in alfalfa under drought. In our study, alfalfa genotypes overexpressing miR156 (miR156OE) exhibited reduced water loss, and enhanced root growth under drought. Our RNA-seq data showed that in response to drought, a total of 415 genes were upregulated and 169 genes were downregulated specifically in miR156OE genotypes. Genotypic comparison revealed that 285 genes were upregulated and 253 genes were downregulated in miR156OE genotypes relative to corresponding WT under drought. Gene Ontology enrichment analysis revealed that the number of differentially expressed genes belonging to biological process, molecular function and cell component functional groups was decreased in miR156OE genotypes under drought. Furthermore, RNA-Seq data showed downregulation of a gene encoding WD40 repeat in a miR156-specific manner. 5' RACE experiments verified cleavage of WD40-2 transcript under drought. Moreover, alfalfa plants overexpressing WD40-2 showed drought sensitive, whereas those with silenced WD40-2 exhibited drought tolerant phenotypes. These findings suggest that miR156 improves drought tolerance in alfalfa by targeting WD40-2.

Effects of TT8 and HB12 Silencing on the Relations between the Molecular Structures of Alfalfa ( Medicago sativa) Plants and Their Nutritional Profiles and In Vitro Gas Production

The objective of this study was to investigate the effects of silencing the TT8 and HB12 genes on the nutritive profiles and in vitro gas production of alfalfa in relation to the spectral molecular structures of alfalfa. TT8-silenced (TT8i, n = 5) and HB12-silenced (HB12i, n = 11) alfalfa were generated by RNA interference (RNAi) and grown with nontransgenic wild type controls (WT, n = 4) in a greenhouse. Alfalfa plants were harvested at early-to-mid vegetative stage. Samples were analyzed for their chemical compositions, CNCPS fractions, and in vitro gas production. Correlations and regressions of the nutritional profiles and in vitro gas production with the molecular spectral structures were also determined. The results showed that the transformed alfalfa had higher digestible fiber and lower crude protein with higher proportions of indigestible protein than WT. HB12 RNAi had lower gas production compared with those of the others. Some chemical, CNCPS, and gas-production profiles were closely correlated with spectral structures and could be well predicted from spectral parameters. In conclusion, the RNAi silencing of TT8 and HB12 in alfalfa altered the chemical, CNCPS and gas-production profiles of alfalfa, and such alterations were closely correlated with the inherent spectral structures of alfalfa.

Maximizing the expression of transgenic traits into elite alfalfa germplasm using a supertransgene configuration in heterozygous conditions

A novel process for the production of transgenic alfalfa varieties. Numerous species of legumes, including alfalfa, are critical factors for agroecosystems due to their ability to grow without nitrogen fertilizers derived from non-renewable fossil fuels, their contribution of organic nitrogen to the soil, and their increased nutritional value. Alfalfa is the main source of vegetable proteins in meat and milk production systems worldwide. Despite the economic and ecological importance of this autotetraploid and allogamous forage crop, little progress has been made in the incorporation of transgenic traits into commercial alfalfa. This is mainly due to the unusually strong transgene silencing and complex reproductive behavior of alfalfa, which limit the production of events with high transgene expression and the introgression of selected events within heterogeneous synthetic populations, respectively. In this report, we describe a novel procedure, called supertransgene process, where a glufosinate-tolerant alfalfa variety was developed using a single event containing the BAR transgene associated with an inversion. This approach can be used to maximize the expression of transgenic traits into elite alfalfa germplasm and to reduce the cost of production of transgenic alfalfa cultivars, contributing to the public improvement of this legume forage and other polyploid and outcrossing crop species.

From model to crop: functional characterization of SPL8 in M. truncatula led to genetic improvement of biomass yield and abiotic stress tolerance in alfalfa

Biomass yield, salt tolerance and drought tolerance are important targets for alfalfa (Medicago sativa L.) improvement. Medicago truncatula has been developed into a model plant for alfalfa and other legumes. By screening a Tnt1 retrotransposon-tagged M. truncatula mutant population, we identified three mutants with enhanced branching. Branch development determines shoot architecture which affects important plant functions such as light acquisition, resource use and ultimately impacts biomass production. Molecular analyses revealed that the mutations were caused by Tnt1 insertions in the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 8 (SPL8) gene. The M. truncatula spl8 mutants had increased biomass yield, while overexpression of SPL8 in M. truncatula suppressed branching and reduced biomass yield. Scanning electron microscopy (SEM) analysis showed that SPL8 inhibited branching by directly suppressing axillary bud formation. Based on the M. truncatula SPL8 sequence, alfalfa SPL8 (MsSPL8) was cloned and transgenic alfalfa plants were produced. MsSPL8 down-regulated or up-regulated alfalfa plants exhibited similar phenotypes to the M. truncatula mutants or overexpression lines, respectively. Specifically, the MsSPL8 down-regulated alfalfa plants showed up to 43% increase in biomass yield in the first harvest. The impact was even more prominent in the second harvest, with up to 86% increase in biomass production compared to the control. Furthermore, down-regulation of MsSPL8 led to enhanced salt and drought tolerance in transgenic alfalfa. Results from this research offer a valuable approach to simultaneously improve biomass production and abiotic stress tolerance in legumes.

Molecular Structural Changes in Alfalfa Detected by ATR-FTIR Spectroscopy in Response to Silencing of TT8 and HB12 Genes

This study investigated the spectral changes in alfalfa molecular structures induced by silencing of Transparent Testa 8 (TT8) and Homeobox 12 (HB12) genes with univariate and multivariate analyses. TT8-silenced (TT8i), HB12-silenced (HB12i) and wild type (WT) alfalfa were grown in a greenhouse under normal conditions and were harvested at early-to-mid vegetative stage. Samples were free-dried and grounded through 0.02 mm sieve for spectra collections with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Afterwards, both univariate and multivariate analyses were conducted on amide, carbohydrate and lipid regions. Univariate results showed that silencing of TT8 and HB12 genes affected peak heights of most total carbohydrate (TC) and structural carbohydrate (STC), and structural carbohydrate area (STCA) in carbohydrate regions; and β-sheet height, amide areas, and ratios of amide I/II and α-helix/β-sheet in amide region; and symmetric CH2 (SyCH2), asymmetric CH2 (AsCH2) and (a)symmetric CH2 and CH3 area (ASCCA) in the lipid region. Multivariate analysis showed that both hierarchy cluster analysis (HCA) and principal component analysis (PCA) clearly separated WT from transgenic plants in all carbohydrate regions and (a)symmetric CH2 and CH3 (ASCC) lipid region. In the amide region, PCA separated WT, TT8i and HB12i into different groups, while HCA clustered WT into a separate group. In conclusion, silencing of TT8 and HB12 affected intrinsic molecular structures of both amide and carbohydrate profiles in alfalfa, and multivariate analyses successfully distinguished gene-silenced alfalfa from its parental WT control.

Molecular Structural Changes in Alfalfa Detected by ATR-FTIR Spectroscopy in Response to Silencing of TT8 and HB12 Genes

This study investigated the spectral changes in alfalfa molecular structures induced by silencing of Transparent Testa 8 (TT8) and Homeobox 12 (HB12) genes with univariate and multivariate analyses. TT8-silenced (TT8i), HB12-silenced (HB12i) and wild type (WT) alfalfa were grown in a greenhouse under normal conditions and were harvested at early-to-mid vegetative stage. Samples were free-dried and grounded through 0.02 mm sieve for spectra collections with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Afterwards, both univariate and multivariate analyses were conducted on amide, carbohydrate and lipid regions. Univariate results showed that silencing of TT8 and HB12 genes affected peak heights of most total carbohydrate (TC) and structural carbohydrate (STC), and structural carbohydrate area (STCA) in carbohydrate regions; and β-sheet height, amide areas, and ratios of amide I/II and α-helix/β-sheet in amide region; and symmetric CH2 (SyCH2), asymmetric CH2 (AsCH2) and (a)symmetric CH2 and CH3 area (ASCCA) in the lipid region. Multivariate analysis showed that both hierarchy cluster analysis (HCA) and principal component analysis (PCA) clearly separated WT from transgenic plants in all carbohydrate regions and (a)symmetric CH2 and CH3 (ASCC) lipid region. In the amide region, PCA separated WT, TT8i and HB12i into different groups, while HCA clustered WT into a separate group. In conclusion, silencing of TT8 and HB12 affected intrinsic molecular structures of both amide and carbohydrate profiles in alfalfa, and multivariate analyses successfully distinguished gene-silenced alfalfa from its parental WT control.