Alternative splicing of PeGA20ox1 impairs PeRAP2-1-mediated GA/ABA homeostasis leading to short internodes in the dwarf variant of Moso bamboo, Phyllostachys edulis 'Heterocycla'.

Internode morphology critically determines bamboo wood quality. Phyllostachys edulis 'Heterocycla' (GJ) is a natural dwarf mutant of P. edulis (WT), yet regulatory mechanisms remain unclear. Here, we show that impaired parenchyma cell elongation is the primary cellular basis for dwarfism in GJ. This phenotype correlates with a marked reduction in gibberellin (GA) and an increase in abscisic acid (ABA) levels. Through weighted gene co-expression network analysis, we identified PeGA20ox1 as a critical regulator of internode elongation. In GJ, PeGA20ox1 undergoes alternative splicing (AS), producing a transcript, PeGA20ox1-GJ, with a premature termination codon. Moreover, we characterized that a bifunctional transcription factor PeRAP2-1 mediates GA/ABA homeostasis, which is an activator of PeABA3 and an inhibitor of PeGA20ox1 by binding to different cis-acting elements. Intriguingly, this AS event results in the loss of function of PeGA20ox1-GJ, which disrupts the PeRAP2-1-mediated hormonal balance, ultimately inhibiting internode elongation. This study suggests that the posttranscriptional regulation induced by AS may adapt to the rapid growth of bamboo plants and provides important genetic resources for the molecular breeding of bamboo with improved culm traits.