Unraveling the mechanism of adventitious bud formation in sugarcane spontaneous adventitious bud (SAB) mutant.

The spontaneous adventitious bud (SAB) mutant of sugarcane, which forms clustered buds on the stem, provides a unique system for elucidating the mechanisms underlying in vivo regeneration and plant meristem differentiation anomalies. The present study investigated the mechanism underlying SAB formation in the sugarcane mutant 'YZ2018-81' through an integrated approach combining histological analysis, endogenous hormone profiling, and RNA-sequencing. Histological analysis revealed that the adventitious buds originated from the dedifferentiating cortical parenchyma cells, following a developmental sequence of dedifferentiation, proliferation, callus-like protrusion formation, and bud differentiation. Further profiling of the endogenous hormones revealed significantly elevated levels of trans-zeatin (tZ) in the second internode below the shoot apical meristem (SAM) (the 2nd IN) and upper stem nodes (the sixth internode below the SAM, the 6th IN), respectively, abscisic acid (ABA), and auxin (IAA) but lower levels of isopentenyladenine (IP) and jasmonic acid (JA) in SAB than in CK, suggesting synergistic roles for tZ, IAA, and ABA in bud initiation, and the inhibitory role of JA in cell division. Meanwhile, elevated gibberellin (GA3) in the 6th IN indicated its participate in promoting bud elongation in the SAB mutant. Transcriptome analysis identified 20,858 differentially expressed genes (DEGs) in the samples, including upregulated genes such as meristem development regulators (RS1, REL2, and DCL), hormone signaling components (ARFs and RRs), and regeneration factors (GRF10, PLT2, and CYCD2-2). These DEGs were enriched in "plant hormone signal transduction" and "MAPK signaling pathway". The heterologous overexpression of ScGRF10 in rice induced ectopic roots at stem nodes, confirming its involvement in ectopic organogenesis. Our work elucidates the cellular, hormonal, and transcriptional framework of in vivo bud regeneration in sugarcane. The mutant also serves as a novel model for monocot regeneration and valuable genetic resources for enhancing sugarcane biotechnology.