Deciphering molecular mechanisms involved in salinity tolerance in guar (Cyamopsis tetragonoloba (L.) Taub.) using transcriptome analyses

Authors: ACHARYA, BISWA - University Of California; Sandhu, Devinder; DUEÑAS, CHRISTIAN - University Of California; Ferreira, Jorge; GROVER, KULBHUSHAN - New Mexico State University

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2022
Publication Date: 1/22/2022
Citation: Acharya, B.R., Sandhu, D., Dueñas, C., Ferreira, J.F., Grover, K.K. 2022. Deciphering molecular mechanisms involved in salinity tolerance in guar (Cyamopsis tetragonoloba (L.) Taub.) using transcriptome analyses. Plants. 11(3). Article 291. https://doi.org/10.3390/plants11030291.
DOI: https://doi.org/10.3390/plants11030291

Interpretive Summary: Guar is a legume crop, which is primarily grown in resource-deficient conditions in semiarid and arid regions because of its drought and heat tolerance. The whole plant is used as protein-rich forage for animals, and beans are commonly used for human consumption due to their high nutritional value. In addition, the endosperm of guar seeds is a rich source of guar gum. Guar gum is an important industrial crop used in various industries, including food, textile, petroleum, natural gas, mining, pharmaceutical, cosmetics, paper, and paint. The productivity of guar is negatively affected by salinity. Hence, identification and molecular analysis of salt-tolerant genotypes are essential for crop productivity under saline conditions. To study molecular mechanisms of salinity tolerance in guar, we employed RNA-Sequencing (RNA-Seq) approach to study salinity-regulated transcriptomes in leaves and roots of a salt-tolerant genotype Matador (genotype 03) and a salt-sensitive genotype PI 340261 (genotype 22) under control and salinity conditions. Our analyses suggested that expression differences between salt treatment and control were more pronounced than between two genotypes. Transcriptome analysis and phenotypic and physiological characterizations of salt-tolerant and salt-sensitive genotypes helped understand the importance of different pathways critical for salinity tolerance in guar. A wide variety of genes contributed toward salinity tolerance in ‘03’ compared to ‘22’, including transporters, hormonal signaling, calcium signaling, redox signaling, and transcription factors. This understanding may become instrumental in developing new guar genotypes tolerant to saline conditions without compromising crop productivity. Hence, our results will help breeders and geneticists develop new salt-tolerant guar varieties, allowing farmers to increase crop yields in marginal lands. Successful guar cultivation in the U.S. will reduce the burden of importing guar gum from foreign countries and increase farmers' profitability by efficiently utilizing marginal soils/waters for crop cultivation.

Technical Abstract: Guar is a commercially important legume crop known for guar gum. Guar is tolerant to various abiotic stresses, but the mechanisms involved in its salinity tolerance are not well established. This study aimed to understand molecular mechanisms of salinity tolerance in guar. RNA sequencing (RNA-Seq) was employed to study the leaf and root transcriptomes of salt-tolerant (Matador) and salt-sensitive (PI 340261) guar genotypes under control and salinity. Our analyses identified a total of 296,114 unigenes assembled from 527 million clean reads. Transcriptome analysis revealed that the gene expression differences were more pronounced between salinity treatments than between genotypes. Differentially expressed genes associated with stress-signaling pathways, transporters, chromatin remodeling, microRNA biogenesis, and translational machinery play critical roles in guar salinity tolerance. Genes associated with several transporter families that were differentially expressed during salinity included ABC, MFS, GPH, and P-ATPase. Furthermore, genes encoding transcription factors/regulators belonging to several families, including SNF2, C2H2, bHLH, C3H, and MYB were differentially expressed in response to salinity. This study revealed the importance of various biological pathways during salinity stress and identified several candidate genes that may be used to develop salt-tolerant guar genotypes that might be suitable for cultivation in marginal soils with moderate to high salinity or using degraded water.