Integrative Multi-Omics Analysis of Barley Genotypes Shows Differential Salt-Induced Osmotic Barriers and Response Phases Among Rootzones

The mechanisms underlying rootzone-localised responses to salinity stress during early stage of barley development remains fragmentary and elusive. Here, we performed a comprehensive detection of the multi-root-omes (transcriptomes, metabolomes, lipidomes) of a domesticated barley cultivar (Clipper) and a landrace (Sahara) with seedling root growth maintained and restricted in response to salt stress, respectively. Novel generalized linear models were designed to determine differentially expressed genes (DEG) or abundant metabolites (DAM) specific to salt treatments, genotypes, or rootzones (meristematic Z1, elongation Z2, maturation Z3). Based on pathway over-representation of the DEG and DAM, phenylpropanoid biosynthesis is the most statistically over-represented biological pathways among all salinity responses observed. Together with the histological evidence, an intense salt-induced lignin impregnation was found only at the stelic cell wall of Clipper Z2, comparing to a unique elevation of suberin deposition across Sahara Z2. This suggests two differential salt-induced modulations of apoplastic flow between the genotypes. Based on global correlation network construction of the DEG and DAM, callose deposition that potentially adjusted the symplastic flow in roots was almost independent of salinity in rootzones of Clipper, but was markedly decreased in that of Sahara. Through closer examinations of molecular and hormonal clues, we further demonstrate that the salinity response in rootzones of Clipper were mostly at recovery phase, comparing to Sahara with rootzones retained at quiescence. Taken together, we propose that two distinctive salt tolerance mechanisms could exist in Clipper (growth-sustaining) and Sahara (salt-shielding), providing important clues for improving crop plasticity to cope with the deteriorating global salinization of soil.