Regulation of chronic hypoxia adaptation by truncated hemoglobin in Moso bamboo (Phyllostachys edulis) shoots

Rapid growth of Moso bamboo shoots relies on efficient energy metabolism, but their dense phloem structure and high oxygen consumption lead to a chronic hypoxic environment. In this study, we measured the oxygen concentration, respiratory metabolism, and analyzed hypoxia-responsive gene expression profiles via RNA-seq in bamboo shoots at different growth stages. Combining molecular dynamics simulation, subcellular localization, and hypoxia stress experiments, we identified a Moso bamboo truncated hemoglobin (PeTrHb) and investigated its potential role in maintaining hypoxic homeostasis. The results revealed that the internal oxygen level of bamboo shoots (0.68–3.60 % [v/v]) was significantly lower than that of soil water (17.48 % [v/v]), and the basal low-oxygen region (meristem-enriched area) overlapped with the region of high PeTrHb1 expression. The percentage of aerobic respiration was only 38–47 % under air treatment, but the ethanol concentration did not significantly increase under nitrogen stress, these findings suggest that bamboo shoots may maintain energy homeostasis through a nonethanol fermentation pathway; PeTrHb1/2 exhibit a superb oxygen affinity ( K a = 10 8 -10 9 M −1 ), and their nucleoplasmic localization characteristics suggest that they may limit mitochondrial oxygen availability by binding free oxygen molecules. Finally, the crucial role of PeTrHb1 in maintaining cell viability under hypoxia was validated in both Moso bamboo and transiently transformed tobacco leaves. Our study identified chronic hypoxia during the growth and development of Moso bamboo shoots and proposed that PeTrHb1 may be involved in regulating oxygen partitioning to maintain hypoxic niches, a mechanism that may avoid the toxic accumulation of ethanol fermentation and provide a new pathway for energy metabolism. These findings provide a reference for future analyses of the relationship between rapid growth and hypoxia tolerance in Moso bamboo. • Oxygen concentrations in Moso bamboo meristems range from 0.68–3.60 % (v/v). • Truncated hemoglobin 1 (TrHb1) expression in Moso bamboo shoots negatively correlates with oxygen levels. • TrHb exhibits ultrahigh oxygen-binding capacity (k a =1.14 × 10 9 –2.11 × 10 8 M −1 ). • TrHb maintains hypoxia by oxygen sequestration and metabolic gene coordination. • TrHb provides a new target for breeding industrial crops tolerant to hypoxia induced by waterlogging stress.