Corm Development Research Articles

Telomere-to-telomere genome assembly of Eleocharis dulcis and expression profiles during corm development

Eleocharis dulcis (Burm. f.) Trin. ex Hensch., commonly known as Chinese water chestnut, is a traditional aquatic vegetable in China, and now is widely cultivated throughout the world because of its high nutritional value and unique tastes. Here, we report the assembly of a 493.24 Mb telomere-to-telomere (T2T) genome of E. dulcis accomplished by integrating ONT ultra-long reads, PacBio long reads and Hi-C data. The reference genome was anchored onto 111 gap-free chromosomes, containing 48.31% repeat elements and 33,493 predicted protein-coding genes. Whole genome duplication (WGD) and inter-genomic synteny analyses indicated that chromosome breakage and genome duplication in E. dulcis possibly occurred multiple times during genome evolution after its divergence from a common ancestor with Rhynchospora breviuscula at ca. 35.6 Mya. A comparative time-course transcriptome analysis of corm development revealed different patterns of gene expression between cultivated and wild accessions with the highest number of differentially expressed genes (DEGs, 15,870) at the middle swelling stage and some of the DEGs were significantly enriched for starch metabolic process.

Understanding the Saffron Corm Development-Insights into Histological and Metabolic Aspects.

The reproduction of Crocus sativus L., a sterile triploid plant, is carried out exclusively through corms, whose size determines the saffron yield. The development of daughter corms (DC) is supported by photoassimilates supplied by the leaves as well as by the mother corms (MC). While biomass partitioning during DC development is well studied, growth dynamics in terms of cell number and size, the involved meristems, as well as carbohydrate partition and allocation, are not yet fully understood. We conducted a comprehensive study into saffron corm growth dynamics at the macroscopic and microscopic levels. Variations in carbohydrate content and enzymatic activities related to sucrose metabolism in sources and sinks were measured. Two key meristems were identified. One is involved in vascular connections between DC and MC. The other is a thickening meristem responsible for DC enlargement. This research explains how the previously described phases of corm growth correlate with variations in cell division, enlargement dynamics, and carbohydrate partitioning among organs. Results also elucidated that the end of DC growth relates to a significant drop in MC root biomass, limiting the water supply for the DC growth, and establishing the onset of leaf wilting. The lack of starch accumulation in aged leaf cells is noteworthy, as is the accumulation of lipids. We hypothesize a signaling role of sugars in DC growth initiation, stop, and leaf aging. Finally, we established a predominant role of sucrose synthase as a sucrolytic enzyme in the maintenance of the high flux of carbon for starch synthesis in DC. Together, the obtained results pave the way for the definition of strategies leading to better control of saffron corm development.

Transcriptional dynamics in source-sink tissues identifies molecular factors regulating the corm development process in saffron (Crocus sativus L.).

Geophytic plants have evolved to develop underground storage organs (USO) in the active growing season to withstand harsh environments as well as to coordinate growth and reproduction when conditions are favourable. Saffron is an autumn flowering geophyte and an expensive spice crop restricted to certain geographical locations in the world. Saffron, being sterile, does not produce seeds and thus propagates only through corms, the quality of which determines its yield. Corm development in saffron is unexplored and the underlying molecular mechanism is still elusive. In this study, we performed an extensive characterisation of the transcriptional dynamics in the source (leaf) and sink (corm) tissues during corm development in saffron. Via morphological and transcriptome studies, we identified molecular factors regulating corm development process in saffron, which defined corm development into three stages: the initiation stage demonstrates enhanced vegetative growth aboveground and swelling of shoot base belowground due to active cell division & carbohydrate storage; the bulking stage comprises of increased source and sink strength, active photosynthesis, circadian gating and starch accumulation; the maturation stage represents reduced source and sink strength, lowered photosynthesis, sugar transport, starch synthesis and cell cycle arrest. The global view of transcriptional changes in source and sink identifies similar and new molecular factors involved in the saffron corm development process compared to USO formation in other geophytes and provides a valuable resource for dissecting the molecular network underlying the corm development. We propose a hypothetical model based on data analysis, of how molecular factors via environmental cues can regulate the corm development process in saffron.

Drought Stress Inhibits Starch Accumulation in Taro (Colocasia esculenta L. Schott).

Colocasia esculenta L. Schott is a main traditional root crop in China, serving as an important vegetable and staple food. Drought stress plays vital role on the growth and development of taro corm. Two different varieties of taro in Jiangsu were selected: Xiangsha taro and Longxiang taro. The accumulation characteristics, morphological structure, and physicochemical properties of taro corm starch were studied by microscopic observation, particle size analysis, and X-ray diffractometer (XRD) analysis. Transcriptome analyses were used to identify the related genes of taro corm under drought stress. During the growth of taro, the number of amyloplasts showed an obvious increasing trend and shifted from being dispersed throughout the cells to being gathered on one side of the cells, and morphological observations showed that smaller granular distribution gradually changed to a larger lumpy distribution. The particle size of Longxiang taro is smaller than that of Xiangsha taro. Under drought stress conditions, the occurrence of starch grains and corm size were inhibited in Xiangsha taro. Transcriptome sequencing of drought-stressed taro corms showed that the enzymes related to starch synthesis were differentially expressed. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of drought-stressed taro corms showed that drought affected hormone signal transduction, material metabolism, drought stress tolerance, plant growth and development, and stress resistance, which triggered the plant drought adaptive response. Drought stress inhibits starch accumulation in taro.

Development and yield of cormels gladiolus plant stimulated with paclobutrazol

The application of paclobutrazol compounds in several types of horticultural crops is effective in stimulation the growth and development of tubers. Gladiolus plant (Gladiolus hybridus) is one of the ornamental plants that produce bulbs or corm and cormels as reproductive organs. The development of corm and cormels gladiolus plants has been stimulated by the concentration of paclobutrazol compounds through soil surface flushing after flowers are harvested, namely at the age of 66 days after planting. Using the single factor Randomized Block Design method with four concentration levels of pacrobutrazol compounds as treatment, namely, 0 mgL-1, 50 mgL-1, 100 mgL-1, and 150 mgL-1. Corm and cormels development was observed destructively in sample plants at regular intervals of five days as many as eight times, starting after a week of watering consisting of variable responses to the development of the corm diameter, the development of the number of cormels, the development of the diameter of the cormels, and the development of the plant root ratio. The data obtained are suspected according to regression fingerprints, and the curves obtained are compared with squeeze and alignment tests. The results showed that the diameter of the corm, the diameter of the cormels, and development of the plant root ratio treated with paclobutrazol compounds were better than without treatment, but the application of paclobutrazol treatment had no effect on the number of cormels. Obtained cormels with a diameter of > 1.5 cm is the desired final goal in this study, because the cormels have economic value as planting material to produce larger corm, then the next can be used as planting material to produce flowering corms.

Comparative metabolomics analysis reveals dynamic changes in carbohydrate profiles of corms during the "relay growth" of konjac (Amorphophallus muelleri).

The type and content of carbohydrates in konjac corms are an essential factors in determining the quality of konjac; however, the pattern of carbohydrate changes and the mechanism regulating the development of mother and daughter corms in the "relay growth" process of Amorphophallus muelleri remain unclear. This study aimed to investigate changes in corm carbohydrates during the growth cycle of A. muelleri and to compare the carbohydrate composition and the expression of related genes between mother and daughter corms. Integrated metabolome and RNA-seq analyses identified 37 differential metabolites as well as 8074 genes that were differentially expressed between mother and daughter corms, the majority of which were involved in starch and sucrose metabolism. More than 80% of the differential metabolites, including sucrose and starch, tended to accumulate in the mother corms; however, konjac glucomannan (KGM), as one of the most important carbohydrates and its major component of the corm, accumulated in higher amounts in the daughter corms. In addition, the expression of invertase and alpha-amylase that promote the breakdown of sucrose and starch was 351.78- and 15.63-fold higher, respectively, in the daughter corm, whereas that of the starch synthesis gene AkWAXY was only 0.096 times as high as in the mother corms. Furthermore, the level of cellulose synthase-like protein G, which promotes KGM synthesis, was 3.85 times higher in daughter corms compared to mother corms. Thus, we inferred that the daughter and mother corms had two distinct carbohydrate utilization strategies. This study provides insights into temporal changes in carbohydrates during the growth cycle of A. muelleri.

Thermal management and energy efficiency analysis of planar-array LED water-cooling luminaires in vertical farming systems for saffron

For saffron (Crocus sativus L.) in vertical farming systems, improper design of LED lighting system may cause the variation of ambient temperature and subsequent influence of development and flowering of corms on the upper space. In the present study, blue-red (B–R) and white (W) planar-array LED luminaires were designed and fabricated with water-cooling system to solve the thermal management problem. LED modules and flow path in luminaires were calculated through the models of point heat source and non-isothermal flow in simulation software. And the temperature field distribution in saffron culture shelf system and the subsequent effect on corm developments were evaluated for the luminaires with three types of structures. The LED water-cooling luminaires without power supplies and dimming control systems (WCL-PS) demonstrated the best thermal management, because the temperature around saffron corms would not be interfered by the heat from the luminaires. Additionally, experiments were conducted to verify the simulation models, with less than 2.4 °C in the maximum deviation. LED modules were also measured as outstanding radiant performance. The photosynthetic photon flux efficacy (PPFE) was respectively 2.74 μmol J−1 for B-LED at 450 nm, 1.65 μmol J−1 for R-LED at 660 nm, as well as 2.75 μmol J−1 for W-LED at correlated color temperature (CCT) 3000 K. At last, white-LED luminaire had a higher PPFE, a lower power consumption and a better temperature field distribution in contrast with blue-red luminaire, which were more recommended for saffron in vertical farming systems.

ASSESSMENT OF BIOLOGICAL DAMAGE AND TOXIC POTENCY OF COLCHICINE IN GLADIOLUS (GLADIOLUS GRANDIFLORUS) PLANTS

Colchicine is one of the important aqueous solutions that has been used to induce mutation or ploidy in many plant species long ago. However, its proper concentrations plays a vital role, increased or inappropriate concentrations may cause mortality, stunted growth, morphological deformation, etc. in plant species. Thus, this study was conducted to evaluate the different colchicine concentrations on the growth and development of gladiolus corms. Gladiolus corms were treated with 0.2%, 0.4%, and 0.6% concentrations for 24 hours. Colchicine toxicity was evaluated during the early growth stage showed a higher concentration of 0.6% significantly reduced corm survival (47%) and caused a 51.9% survival reduction over control. In terms of growth parameters, all concentrations of colchicine reduced plant height with a number of leaves along with inducing different forms of morphological abnormalities and chlorophyll mutants. To optimize the dose for successful ploidy induction, LD30 and LD50 on mortality rate through an analysis were calculated to be 0.31% and 0.57% whereas GR50 based on plant height and the number of leaves reduction was found to be 0.17% and 0.34%. Hence, the results from this study could be used in the future for further breeding programs by reducing the genotoxicity of colchicine on gladiolus.

Responses to defoliation and fertiliser, corm development and chemical control of onion grass (Romulea rosea) in the Mediterranean environment of southern Australia

AbstractBackgroundOnion grass (Romulea rosea) is a common weed that infests native and improved pastures in the Mediterranean environments of southern Australia. It is a very challenging weed to control due to its distinctive growth and survival mechanisms involving corms.MethodsThree glasshouse experiments were conducted in Australia to investigate the response of onion grass to defoliation and fertiliser application, the development and growth of onion grass corms and the chemical control of the weed in winter and spring.ResultsDefoliating consistently to 1 cm above ground reduced corm weight by 84% compared with the control. Medium or high fertiliser application did not increase herbage mass of onion grass compared with the nonfertilised treatment. The corm weight of onion grass declined from Weeks 1 to 8 after emergence, remained at 53–60 mg dry matter (DM) corm−1 from Weeks 8 to 19 and then declined on average to 37 mg DM corm−1 up to Week 26 after emergence. New corms started to develop at Week 6 after emergence. A small proportion of the onion grass plants (7.5%) developed multiple new corms (3–6 corms) from a single old corm. The most effective herbicide control was a winter application of metsulfuron methyl or imazamox as an alternative product to protect clover.ConclusionsThis study has identified the growth and development patterns of onion grass corms, how the plant responded to defoliation and fertiliser application and effective chemical control of this weed. These findings have significant practical implications for the improvement of onion grass‐infested pastures.

A chromosome-level genome assembly of Amorphophallus konjac provides insights into konjac glucomannan biosynthesis

Amorphophallus konjac, a perennial herb in the Araceae family, is a cash crop that can produce a large amount of konjac glucomannan. To explore mechanisms underlying such large genomes in the genus Amorphophallus as well as the gene regulation of glucomannan biosynthesis, we present a chromosome-level genome assembly of A. konjac with a total genome size of 5.60 Gb and a contig N50 of 1.20 Mb. Comparative genomic analysis reveals that A. konjac has undergone two whole-genome duplication (WGD) events in quick succession. Two recent bursts of transposable elements are identified in the A. konjac genome, which contribute greatly to the large genome size. Our transcriptomic analysis of the developmental corms characterizes key genes involved in the biosynthesis of glucomannan and related starches. High expression of cellulose synthase-like A, Cellulose synthase-like D, mannan-synthesis related 1, GDP-mannose pyrophosphorylase and phosphomannomutase fructokinase contributes to glucomannan synthesis during the corm expansion period while high expression of starch synthase, starch branching enzyme and phosphoglucomutase is responsible for starch synthesis in the late corm development stage. In conclusion, we generate a high-quality genome of A. konjac with different sequencing technologies. The expansion of transposable elements has caused the large genome of this species. And the identified key genes in the glucomannan biosynthesis provide valuable candidates for molecular breeding of this crop in the future.

Comparative Transcriptome Sequencing of Taro Corm Development With a Focus on the Starch and Sucrose Metabolism Pathway

Taro (Colocasia esculenta) is an important tuber crop and staple food. Taro corms have higher nutritional value and starch contents as compared to most of the other root/tuber crops. However, the growth and development of the taro rhizome have not been critically examined in terms of transcriptomic signatures in general or specific to carbohydrates (starch and sucrose) accumulation. In current study, we have conducted a comprehensive survey of transcripts in taro corms aged 1, 2, 3, 4, 5, and 8 months. In this context, we have employed a whole transcriptome sequencing approach for identification of mRNAs, CircRNAs, and miRNAs in corms and performed functional enrichment analysis of the screened differentially expressed RNAs. A total of 11,203 mRNAs, 245 CircRNAs, and 299 miRNAs were obtained from six developmental stages. The mRNAs included 139 DEGs associated with 24 important enzymes of starch and sucrose metabolism. The expression of genes encoding key enzymes of starch and sucrose metabolism pathway (GBSS, AGPase, UGPase, SP, SSS, βFRUCT and SuSy) demonstrated significant variations at the stage of 4 months (S4). A total of 191 CircRNAs were differentially expressed between the studied comparisons of growth stages and 99 of these were associated with those miRNA (or target genes) that were enriched in starch and sucrose metabolism pathway. We also identified 205 miRNAs including 46 miRNAs targeting DEGs enriched in starch and sucrose biosynthesis pathway. The results of current study provide valuable resources for future exploration of the molecular mechanisms involved in the starch properties of Taro.

Uncovering the mechanism preliminarily of formation and development of taro corm in vitro by morphological physiology and transcriptomic analysis

In vitro virus-free corms as propagules provide a feasible alternative to the convenient transport and the high survival rate of transplant for typical asexual crop of taro (Colocasia esculenta (L.) Schott). However, the mechanism of formation and expansion of in vitro corm remains unclear. In this study, in vitro corms were obtained from virus-free test-tube plantlet of taro in optimized induced medium (Murashige-Skoog medium + 2 mg L−1 6-Benzylaminopurine + 0.5 mg L−1 1-naphthalene acetic acid + 3% sucrose) (OIM), and then inoculated into the medium with Murashige-Skoog medium + 8% sucrose (MS8) for corm expansion. During this process, morphological observations by paraffin section, plant growth regulators (PGRs) content determination by enzyme-linked immunosorbent assay, and transcriptome assay by Illumina platform were carried out at days 0 (T0), 45 (T1), 90 (T2), and 135 (T3) under different corm expansion stages. The results showed that parenchymal cells enlarge continuously, accompanied with starch particles increase during corm expansion. Besides, three PGRs of indoleacetic acid (IAA), zeatin-riboside (ZR), and abscisic acid (ABA) were positively correlated with corm expansion, the contents of IAA and ABA remained at a high level. Moreover, the transcriptome results showed that plant hormone signal transduction and the starch and sucrose metabolism pathways are enriched significantly based on Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The genes (SBE2.2, GBSS, SUS4), related to starch biosynthesis were up-regulated, meanwhile, three genes of AMYs involved in starch metabolism were down-regulated, which probably promote starch accumulation and corms expansion. Eight genes from plant hormone signal transduction and the starch and sucrose metabolism pathway were selected randomly to validate the result of RNA-seq, and the RT-qPCR results were consistent with the RNA-seq data. These results will provide valuable information for uncovering the mechanism of in vitro corm expansion.

Antagonism between abscisic acid and gibberellin regulates starch synthesis and corm development in Gladiolus hybridus

Understanding corm development in flower bulbs is of importance for securing the quality of cut flowers and propagation of commercial stocks. Gladiolus is one of the most popular bulb plants worldwide. Its corm development is characterized by starch accumulation. Previous research has shown that phytohormones (especially gibberellin (GA)) are involved in tuber development. However, the relationship between abscisic acid (ABA)/GA and starch during corm development remains unclear. To gain deeper insights into the biological process of corm development, we performed a detailed anatomical characterization of different stages of corm development and analyzed phytohormone levels. Our study showed that corm development is linked to hormones (ABA and GA) and carbohydrates (sucrose and starch). Exogenous hormone treatment and silencing of endogenous hormone biosynthesis genes indicated that ABA positively regulates corm development, while GA acts as an antagonist of ABA function. A sucrose synthase gene (GhSUS2) was shown to be involved in the antagonism between ABA and GA. GhSUS2 was upregulated by ABA and downregulated by GA. The increase in the transcript level of GhSUS2 coincided with the development of corm/cormels. Silencing of GhSUS2 repressed corm development and starch accumulation. In conclusion, we propose that GhSUS2, an essential enzyme in sucrose degradation, is differentially regulated by ABA and GA and controls corm development in Gladiolus.

Effect of gypsum and micronutrients on spike and corm yield of gladiolus (Gladiolus grandiflorus ) cv. Guvari

Gladiolus is a nutrient responsive crop that requires major and micro-nutrients viz. N, P, K, Zn, Mn, Fe, B, along with gypsum significantly improves the growth, flowering, yield and quality of corms. In addition, gypsum acts as a source of calcium and soil loosening factor that is needed for corm development. Hence, field experiment was conducted during 2019-2020 at Department of Horticulture, Annamalai University, Tamil Nadu, India on gladiolus cv. Guvari to maximize the yield and quality of spikes and corms. The treatments comprised of ten different combinations of recommended dose of fertilizers (120:150:150 kg/ha NPK), Gypsum (100, 200 and 300 kg/ha) and foliar application of FeSO4, MnSO4 ZnSO4 and HBO(0.5% each in single spray on 30 days 44, 4 33 after planting (DAP) and two sprays on 30 and 45 DAP laid out in Randomized Block Design with three replications. The growth, flowering, and corm yield parameters were periodically assessed. The results revealed that application of gypsum and micronutrients significantly increased the vegetative growth, flowering, spike yield, and corm yield. Application of 300 Kg/ha gypsum was found effective when compared to low doses. Among the ten treatments, application of 120:150:150 kg/ha NPK + 300 kg/ha Gypsum + foliar spray of (0.5% each) FeSO4, MnSO4 ZnSO4 and H3BO3 at 30 and 45 DAP found most 44, 4 33 effective with higher plant height, leaf area, root dry weight, dry matter production, spike length, floret diameter, spike yield, and number of marketable spikes per plant. The corm yield parameters including corm weight, number of daughter corms per plant, number of cormels per plant and weight of daughter corms were also superior in this treatment. Hence, it is confirmed that the application of 300 kg/ha gypsum + foliar spray of (0.5% each) FeSO4, MnSO4ZnSO4 and H3BO3 at 30 and 45 days after planting P along 44, 4 33 with 120:150:150 kg/ha NPK proved maximizing the spike and corm yield of gladiolus.

Enzymatic and transcriptomic analysis reveals the essential role of carbohydrate metabolism in freesia (Freesia hybrida) corm formation

Starch and sucrose metabolism plays a crucial role in the formation and development of bulbs in bulbous plants. However, these mechanisms remain unclear and unexplored in the corms of Freesia hybrida. Herein, we investigated the dynamics of the major form of carbohydrates and related enzyme activities and profiled the transcriptome of freesia corms at four developmental stages with the aim to reveal the relation between the expression of genes involved in the metabolism of carbohydrates and the accumulation of carbohydrates in corm developmental stages for further exploring the mechanism on the starch and sucrose metabolism regulating the formation and development of corms in F. hybrida. The content of starch, sucrose and soluble sugars followed an overall upward trend across the corm developmental stages. Activities of the adenosine diphosphoglucose pyrophosphorylase, starch branching enzyme and β-amylase generally followed the pattern of the starch and sucrose levels. Activities of sucrose phosphate synthase increased from corm formation till the initial swelling stage and subsequently reached a plateau. Activities of invertase and sucrose synthase peaked at the later rapid swelling stage. These suggested that the starch and sucrose dynamics paralleled corm swelling under the action of metabolic enzymes. A total of 100,999 unigenes were assembled in the transcriptomic analysis, and 44,405 unigenes of them were annotated. Analysis based on Clusters of Orthologous Groups suggested that carbohydrate transport and metabolism (9.34% of the sequences) was prominent across the corm developmental process. In total 3,427 differentially expressed genes (DEGs) were identified and the enrichment analysis detected starch and sucrose metabolism as a critical pathway in corm development, especially at the rapid swelling stage. Further, DEGs encoding key carbohydrate-metabolizing enzymes were identified and correlated to enzyme activities and carbohydrate accumulation. The results construct a valuable resource pool for further molecular-level studies, which are helpful for metabolic regulation of carbohydrates and improvement in F. hybrida.

Cloning and Expression Analysis of <i>EdAGPL1</i> in <i>Eleocharis dulcis</i>

In order to clone the cDNA sequence of water chestnut AGPase large subunit gene ( EdAGPL1 ) and analyze its structural characteristics and its expression in different tissues and corm development of water chestnut. Using water chestnut 'Guilin water chestnut ' as research material. The EdAGPL1 gene was cloned by RT-PCR and analyzed by bioinformatics. The expression of EdAGPL1  in different tissues and corm development process was analyzed by real-time fluorescence quantitative PCR technology. The results showed that the length of the cloned EdAGPL1 gene was 1 744 bp, its open reading frame was 1 599 bp, it encoded 532 amino acids, the protein molecular mass was 58.84 kD, the isoelectric point was 7.54, and it had NTP_transferase and PbH1 domains. The secondary structure was composed of helix (13.72%), for the strand (25.19%) and the loop (61.09%). The tertiary structure consists of 17 α-helices, 34 β-sheets, and 51 β-turn (curl) composition. Homology and phylogenetic analysis showed that the homology of amino acid sequence of EdAGPL1 and other plants AGPL protein was 57.54%~61.64%, and has far evolutionary kinship with other plants. Fluorescence quantitative PCR analysis showed that the expression of EdAGPL1  in different tissues was corm> leaf stem > stolon > root. The expression of EdAGPL1  was the highest in the initial stage of corm development, and then it decreased and remainedstable. The study of this gene will help to clarify the regulation mechanism of starch synthesis in water chestnut and provide a theoretical basis for the breeding of high-starch varieties.

Corm reserve composition during dormancy, sprouting and early plant development of gladiolus (Gladiolus hybridus Hort.)

The changes in corm reserve composition during dormancy, sprouting and early plant development were analysed in four varieties of gladiolus viz., Red Ginger, Little Prince, Sunset Jubilee and Pacifica. The results showed that starch and total lipid content of gladiolus corms were increased to 2.62 and 1.08 mg g−1 f.w., respectively during sprouting stage and after that declined in regardless of varieties. While protein content decreased during sprouting of corms (1.76mg g−1 f.w.) and then increased during early plant development (2.20 mg g−1 f.w.). Total phenol content was increased progressively from dormant (10.06 mg g−1 f.w.) to early plant development stage (14.43 mg g−1 f.w.). The results of the study highlighted the potential of these gladiolus species (corms) has been established, based on the synthesis and accumulation pattern of bioactive constituents during sprouting and early plant development of gladiolus corm.

Transcript profiling of carotenoid/apocarotenoid biosynthesis genes during corm development of saffron (Crocus sativus L.).

The dried stigmas of saffron constitute the world's costliest spice. Saffron has many therapeutic applications due to the presence of apocarotenoids. The latter are synthesized at different stages of development, and the biosynthetic pathway involves several genes encoding different enzymes. In order to understand the differential expression of various genes of the pathway, eight distinct developmental stages (S1-early to S8-late) were identified. The corms were assorted into three groups (I, II, and III) based on corm weight. Expression profiles of 12 carotenoid/apocarotenoid genes were studied. The expression of all genes was minimum/least in groups I and II corms during bud development. Lowest expression of carotenogenic genes (CsPSY, CsPDS, CsZDS, CsCRTISO, CsLYC-β1, CsLYC-ε, CsBCH2, and CsNCED) was observed during early stages (S1-S3) of corm growth (dormant period). In group III corms, increased expression of apocarotenoid genes (CsZCO, CsCCD2, CsUGT, and CsALDH) was observed during S4 to S8 stages (reproductive period, floral differentiation). Besides, expression profiles of genes in apical and axillary buds were also examined. Of all the genes studied, apocarotenoid biosynthesis genes (CsBCH2, CsZCO, CsCCD2, CsALDH, and CsUGT) were found to be upregulated in apical bud than in the axillary bud. The results indicated that interaction of phytohormones and sugars, mother corm reserves and the influence of internal and external factors may be contributing to the growth of saffron corm/bud. The study has laid a foundation for further research on the molecular mechanisms underlying bud dormancy/growth in saffron.

Irrigation schedule for maximum corm yield and water productivity in elephant foot yam (Amorphophallus paeoniifolius)

Field experiments were carried out on elephant foot yam [Amorphophallus paeoniifolius (Dennst.) Nicolson] during 2013-2014 and 2014-2015 to study the effect of different irrigation schedules in order to arrive at an optimum schedule for attaining maximum corm yield and water productivity. Two methods (Drip and Flood methods ) and two levels of irrigation (75% and 100% pan evaporation) were applied at different stages of growth as first 12 weeks, 13-24 weeks, 1-24 weeks, 75% during first 12 weeks and 100% during 13-24 weeks after planting and vice versa. Whole corm size of 500 g each of the variety 'Gajendra' was uniformly used as the planting material. Pooled analysis of the data showed superiority of drip irrigation over flood irrigation. Among the treatment combinations, drip irrigation at 100% pan evaporation during 13-24 weeks after planting resulted in the maximum corm yield (40.59 t/ha). However, this was at par with drip or flood irrigation given during the entire period of 1-24 weeks at 75% and 100% levels. Drip irrigation at 100% pan evaporation during 13-24 weeks resulted in maximum water productivity (4.57 kg/m3). Under flood irrigation, maximum water productivity recorded was 3.87 kg/m3. Irrigation during 13-24 weeks after planting coinciding with corm development stage was found to be more critical than irrigation given during the initial stages of planting. The study revealed that drip irrigation at 100% pan evaporation during 13-24 weeks after planting is the most ideal for attaining maximum corm yield and water productivity in elephant foot yam.

Discovery of UDP-Glycosyltransferases and BAHD-Acyltransferases Involved in the Biosynthesis of the Antidiabetic Plant Metabolite Montbretin A.

Plant specialized metabolism serves as a rich resource of biologically active molecules for drug discovery. The acylated flavonol glycoside montbretin A (MbA) and its precursor myricetin 3-O-(6'-O-caffeoyl)-glucosyl rhamnoside (mini-MbA) are potent inhibitors of human pancreatic α-amylase and are being developed as drug candidates to treat type-2 diabetes. MbA occurs in corms of the ornamental plant montbretia (Crocosmia x crocosmiiflora), but a system for large-scale MbA production is currently unavailable. Biosynthesis of MbA from the flavonol myricetin and MbA accumulation occur during early stages of corm development. We established myricetin 3-O-rhamnoside (MR), myricetin 3-O-glucosyl rhamnoside (MRG), and mini-MbA as the first three intermediates of MbA biosynthesis. Contrasting the transcriptomes of young and old corms revealed differentially expressed UDP-sugar-dependent glycosyltransferases (UGTs) and BAHD-acyltransferases (BAHD-ATs). UGT77B2 and UGT709G2 catalyze the consecutive glycosylation of myricetin to produce MR and of MR to give MRG, respectively. In addition, two BAHD-ATs, CcAT1 and CcAT2, catalyze the acylation of MRG to complete the formation of mini-MbA. Transcript profiles of UGT77B2, UGT709G2, CcAT1, and CcAT2 during corm development matched the metabolite profile of MbA accumulation. Expression of these enzymes in wild tobacco (Nicotiana benthamiana) resulted in the formation of a surrogate mini-MbA, validating the potential for metabolic engineering of mini-MbA in a heterologous plant system.