Salinity induces discontinuous protoxylem by a DELLA-dependent mechanism promoting salt tolerance in Arabidopsis seedlings

Abstract

SummarySalinity is detrimental to plants and developmental adjustments limiting salt uptake and transport is therefore important for acclimation to high salt. These parameters may be influenced by xylem morphology, however, how plant root xylem development is affected by salt stress remains unclear.Through detailed phenotypic analyses, molecular and genetic techniques, we demonstrate that salt causes distinct effects on Arabidopsis seedling root xylem, and reveal underlying molecular mechanisms.Salinity causes intermittent inhibition of protoxylem cell differentiation, generating protoxylem gaps, in Arabidopsis and other eudicot seedlings. The extent of protoxylem gaps positively correlates with salt tolerance. Reduced gibberellin signaling is required for protoxylem gap formation. Mutant analyses reveal that the xylem differentiation regulator VASCULAR RELATED NAC DOMAIN 6 (VND6), along with secondary cell wall-producing and cell wall modifying enzymes, including EXPANSIN A1 (EXP1), are involved in protoxylem gap formation, in a DELLA-dependent manner.Salt stress impacts seedling survival and formation of protoxylem gaps is a means of enhancing salt tolerance. Salt stress likely reduces levels of bioactive gibberellins, stabilizing DELLAs, which in turn activate multiple factors modifying protoxylem differentiation. Formation of protoxylem gaps is induced in diverse eudicot species suggesting that this is an evolutionary conserved response for salt acclimation in seedlings.