Transcript analysis of two spinach cultivars reveals the complexity of salt tolerance mechanisms

Authors: ZHAO, CHAOYANG - University Of California; Sandhu, Devinder; Ferreira, Jorge

Submitted to: ACS Agricultural Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2021
Publication Date: 1/29/2021
Citation: Zhao, C., Sandhu, D., Ferreira, J.F. 2021. Transcript analysis of two spinach cultivars reveals the complexity of salt tolerance mechanisms. ACS Agricultural Science and Technology. 1(2):64-75. https://doi.org/10.1021/acsagscitech.0c00063.
DOI: https://doi.org/10.1021/acsagscitech.0c00063

Interpretive Summary: Modern agriculture is constrained by many resource issues and human practices, among which, soil salinization is a widespread and important one that can substantially reduce plant productivity. Most of the research to understand salt tolerance mechanisms in plants is mainly focused on model species such as Arabidopsis. Thus, genetic and molecular responses to salinity in spinach, an agronomically important crop, will help plant breeders develop new salinity-tolerant varieties. Spinach is an economically important vegetable crop that is extremely rich in many core nutrients. Besides, spinach is an excellent source of antioxidant compounds providing important health benefits to humans. In this study, we explored gene expression changes in roots and leaves of two spinach varieties differing in their salt tolerance, exposed to irrigation with either high- or low-salinity water treatments. RNA of 24 spinach samples was sequenced, which led to the identification of several candidate genes involved in salinity stress. These include genes involved in ion uptake, ion movement, calcium signaling, and hormonal signaling. Further studies focusing on these genes may allow geneticists and molecular biologists to develop a deeper understanding of different factors involved in salinity stress and help plant breeders develop new salt-tolerant spinach varieties, which will enable farmers to grow spinach in marginal lands and/or with recycled waters.

Technical Abstract: Increasing soil salinization threatens global crop productivity. An understanding of the genetic networks involved in salinity tolerance mechanisms of high-value crops, such as spinach, is lacking. RNA-Seq analysis of leaves and roots of two spinach genotypes, Monstrans Viroflag and Palek, subjected to high-salinity irrigation, revealed that a higher degree of differential gene expression was caused by salinity rather than by genotype. Genotypic comparisons suggested that the low salt tolerance index for root and shoot biomass of Palek, compared to Monstrans Viroflag, was due to the differential expression of genes involved in water/nutrient uptake rather than tissue salt accumulation. Montrans Viroflag displayed a better Cl- exclusion than Palek and was more efficient in restricting Na+ from entering its roots, thus protecting leaves from ion toxicity. In addition, differentially expressed genes (DEGs) involved in MAPK signaling, hormonal signaling, and transport revealed salinity- and genotype-specific differences and resulted in the identification of candidate genes that may function to mediate ion influx across cell membranes to maintain osmotic homeostasis when plants are under salt stress. The quantitative reverse transcription assay validated the overall expression trends of the selected RNA-Seq-based DEGs among different spinach samples. Collectively, the assays used in this study highlighted the complexity of the salinity tolerance mechanism and isolated several putative genes with the potential to improve salinity tolerance in spinach.