(100-95) Specificity in root domain-accumulation of Phytoglobin1 and nitric oxide (NO) determines meristematic viability in water-stressed Brassica napus roots.
research Associate University of Manitoba Winnipeg, Manitoba, Canada
Body of Abstract: Brassica napus is an economically relevant species with high susceptibility to water stress. To further explore the function of the nitric oxide (NO) scavenger, phytoblobin, we generated B. napus lines over-expressing [BnPgb1(S)] or down-regulating [BnPgb1(A)] BnPgb1, and exposed them to polyethylene glycol (PEG)-induced drought. During the stress, BnPgb1 protein accumulates preferentially in the peripheral domains of the elongation zone, exposing the meristem to NO, which inhibits auxin polar transport (PAT), likely by interfering with PIN1 endomembrane trafficking, and synthesis of auxin. Diminished auxin at the root tip depresses the synthesis of BRs and causes the degradation of the RAM and inhibition of root growth. The strength of BnPgb1 signal in the elongation zone is increased in BnPgb1(S) roots, where BnPgb1 also impinges partially in the meristematic region excluding the RAM. In these roots NO is confined to the most apical cells of the root. Consequently, PAT and auxin synthesis are retained, and the integrity of the RAM is preserved. The auxin preservation of the RAM (through BnPgb1) requires BRs. Inhibition of BRs synthesis with Brassinazole (BrZ) causes the degeneration of the RAMs in dehydrating BnPgb1(S) roots, and reversion of the positive effects of exogenous auxins on the structure of the RAMs. However, BRs alone are not sufficient to rescue drought-damaged RAMs in environments depleted of auxin. Overall, this study emphasizes the importance of tissue-specific localization of BnPgb1 and NO for root drought survival, and provides a preliminary model integrating auxin and BRs in the BnPgb1 in the preservation of meristematic cells.