S: Grafting is a highly useful technique, and its success largely depends on graft union formation. In this study, we found that root-specific expression of the auxin biosynthetic gene iaaM in tobacco, when used as rootstock, resulted in more rapid callus formation and faster graft healing. However, overexpression of the auxin-inactivating iaaL gene in rootstocks delayed graft healing. We observed increased endogenous auxin levels and auxin-responsive DR5::GUS expression in scions of WT/iaaM grafts compared with those found in WT/WT grafts, which suggested that auxin is transported upward from rootstock to scion tissues. A transcriptome analysis showed that auxin enhanced graft union formation through increases in the expression of genes involved in graft healing in both rootstock and scion tissues. We also observed that the ethylene biosynthetic gene ACS1 and the ethylene-responsive gene ERF5 were upregulated in both scions and rootstocks of the WT/iaaM grafts. Furthermore, exogenous applications of the ethylene precursor ACC to the junction of WT/WT grafts promoted graft union formation, whereas application of the ethylene biosynthesis inhibitor AVG delayed graft healing in WT/WT grafts, and the observed delay was less pronounced in the WT/iaaM grafts. These results demonstrated that elevated auxin levels in the iaaM rootstock in combination with the increased auxin levels in scions caused by upward transport/diffusion enhanced graft union formation and that ethylene was partially responsible for the effects of auxin on grafting. Our findings showed that grafting success can be enhanced by increasing the auxin levels in rootstocks using transgenic or gene-editing techniques.

Root sprouts—the formation of new shoots from roots—is an important mechanism for local gene flow from poplar (Populus spp). An effective strategy to reduce root sprout formation could therefore help to ensure containment during field research and commercial deployment of poplar when grown as exotic or transgenic forms. We used a flavonoid glycosyltransferase gene promoter from Scutellaria barbata (SbUGT) to drive the expression of AtCKX2, a cytokinin oxidase from Arabidopsis that converts active to inactive cytokinins in roots of poplar. In the greenhouse, SbUGT::AtCKX2 transgenic plants exhibited a similar shoot growth habit, but had enhanced root growth and fewer root sprouts, compared to the wild-type control and transgenic events with low transgene expression in roots. Under field conditions, the transgenic trees also had similar growth habits and stem growth rates that were not statistically different from wild-type trees over 3 years. Removal of trunks generally induced high rates of root sprouting; however, in selected SbUGT::AtCKX2 transgenic poplar events there was an absence or fewer root sprouts compared to wild-type trees, consistent with the greenhouse results. Our study demonstrates that the SbUGT::AtCKX2 gene can effectively inhibit root sprouting of poplar trees under field conditions, and thus may provide a useful tool to address concerns associated with root-sprouting-mediated transgene spread.

Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f. sp. cubense ( Foc ), threatens global banana production. Lignin reinforces cell walls against pathogens and lodging, yet its regulatory mechanisms in banana remain elusive. Through genome‐wide association study (GWAS) of lignin content across 184 banana accessions, we identified MaERF110 (encoding an AP2/ERF transcription factor) as a key negative regulator. Overexpression of MaERF110 in banana and Arabidopsis significantly reduced lignin deposition, impaired plant structural integrity and enhanced susceptibility to Foc TR4. Integrative RNA‐seq, yeast one‐hybrid and electrophoretic mobility shift assays revealed that MaERF110 directly binds the MaMYB308 promoter and activates its transcription. MaMYB308 overexpression similarly suppressed lignin biosynthesis genes and compromised disease resistance. Mechanistically, MaERF110 ‐overexpression plants exhibited disrupted reactive oxygen species (ROS) homeostasis, with elevated H ₂ O ₂ and superoxide anion accumulation, reduced antioxidant enzyme activities and increased cell damage upon pathogen infection. We elucidate a MaERF110‐MaMYB308 transcriptional module that represses lignin biosynthesis and disables lignin‐mediated defence against Foc TR4. This pathway highlights dual roles for lignin in plant architecture and pathogen defence, providing targets for breeding resistant banana cultivars.