Abstract
Guar (Cyamopsis tetragonoloba (L.) Taub.) is an annual legume crop native to India and Pakistan. Seeds of the plant serve as a source of galactomannan polysaccharide (guar gum) used in the food industry as a stabilizer (E412) and as a gelling agent in oil and gas fracturing fluids. There were several attempts to introduce this crop to countries of more northern latitudes. However, guar is a plant of a short photoperiod, therefore, its introduction, for example, to Russia is complicated by a long day length during the growing season. Breeding of new guar varieties insensitive to photoperiod slowed down due to the lack of information on functional molecular markers, which, in turn, requires information on guar genome. Modern breeding strategies, e.g., genomic predictions, benefit from integration of multi-omics approaches such as transcriptome, proteome and metabolome assays. Here we present an attempt to use transcriptome-metabolome integration to understand the genetic determination of flowering time variation among guar plants that differ in their photoperiod sensitivity. This study was performed on nine early- and six delayed-flowering guar varieties with the goal to find a connection between 63 metabolites and 1,067 differentially expressed transcripts using Shiny GAM approach. For the key biomarker of flowering in guar myo-inositol we also evaluated the KEGG biochemical pathway maps available for Arabidopsis thaliana. We found that the phosphatidylinositol signaling pathway is initiated in guar plants that are ready for flowering through the activation of the phospholipase C (PLC) gene, resulting in an exponential increase in the amount of myo-inositol in its free form observed on GC-MS chromatograms. The signaling pathway is performed by suppression of myo-inositol phosphate kinases (phosphorylation) and alternative overexpression of phosphatases (dephosphorylation). Our study suggests that metabolome and transcriptome information taken together, provide valuable information about biomarkers that can be used as a tool for marker-assisted breeding, metabolomics and functional genomics of this important legume crop.
Highlights
Guar (Cyamopsis tetragonoloba (L.) Taub.) seeds serve as a rich source of a galactomannan polysaccharide that is commonly used in food, cosmetic and oil industry worldwide
Analysis using GMD and NIST libraries identified 69 metabolites. These metabolites were merged with the KEGG database Arabidopsis IDs and, a matrix of 63 metabolites was obtained (Table S1)
In the present study we employed ‘omics’ technologies and systems biology, aiming to provide solutions to a key issue that arises in breeding practice
Summary
Guar (Cyamopsis tetragonoloba (L.) Taub.) seeds serve as a rich source of a galactomannan polysaccharide (guar gum) that is commonly used in food, cosmetic and oil industry worldwide. Due to the high commercial value of guar gum, many attempts have been made in the last few decades to introduce this short-day legume crop to the countries in more northern latitudes. Researchers repeatedly reported a common issue – short day plants had delayed flowering under conditions of long photoperiod which led to late seed maturation and, to a significant loss of yield (e.g., [1]). Dissection of genes involved in flowering time of legume species is a complex task due to a large number of genetic factors required for the initiation of the generative phase. The onset of flowering time depends on genetic factors related to the speed of seed germination and the formation of the first true leaf [6]. Focusing not just on the flowering phenotype per se, but rather on the biochemical or metabolic landscape that accompanies transition to flowering in guar can be useful in searching for genes responsible for flowering time in this legume species
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