Stable isotope labelling and gene expression analysis reveal dynamic nitrogen-supply mechanisms for rapid growth of Moso bamboo.

Rapid growth of Moso bamboo (Phyllostachys edulis) shoots (offspring ramet) is primarily fuelled by nitrogen (N) derived from parent ramet and absorbed by rhizome roots. However, the extent to which each N source supports the growth of offspring ramet and the underlying molecular mechanisms of N transport remain unclear. Here, clonal fragments consisting of a parent ramet, an offspring ramet, and an interconnected rhizome were established in a Moso bamboo forest. Additionally, (15)N isotope tracing and transcriptome profiling were conducted concurrently to quantify the N contribution from the parent ramet and rhizome roots to the offspring ramet, and to reveal the molecular mechanisms underlying N transport during rapid growth (i.e. early, peak, branching, and leafing stages). The N acquisition strategy of offspring ramet shifted from being primarily provided by the parent ramet (72.53%) during early stage to being predominantly absorbed by rhizome roots (69.85%) during the leafing stage. Approximately equal N contributions (45.82%-54.18%) from the parent ramet and rhizome roots were observed during peak and branching stages. PeAAP29123 was identified as a key gene for N transport, being most closely correlated with (15)N content. Biomolecular assays demonstrated that PeHDZ23987 could activate the expression of PeAAP29123 via two types of HD-motifs. Overexpression of PeHDZ23987 and PeAAP29123 significantly enhanced N starvation tolerance in transgenic rice with significantly improved N uptake efficiency. Our findings clarify the pattern and mechanisms of N supply for the rapid growth of Moso bamboo offspring ramet and provide transcriptomic evidence for long-distance N transport between clonal ramets.