The AGCVIII kinase Dw2 modulates cell proliferation, endomembrane trafficking, and MLG/xylan cell wall localization in elongating stem internodes of Sorghum bicolor

SUMMARY Stems of bioenergy sorghum (Sorghum bicolor L. Moench.), a drought‐tolerant C4 grass, contain up to 50 nodes and internodes of varying length that span 4–5 m and account for approximately 84% of harvested biomass. Stem internode growth impacts plant height and biomass accumulation and is regulated by brassinosteroid signaling, auxin transport, and gibberellin biosynthesis. In addition, an AGCVIII kinase (Dw2) regulates sorghum stem internode growth, but the underlying mechanism and signaling network are unknown. Here we provide evidence that mutation of Dw2 reduces cell proliferation in internode intercalary meristems, inhibits endocytosis, and alters the distribution of heteroxylan and mixed linkage glucan in cell walls. Phosphoproteomic analysis showed that Dw2 signaling influences the phosphorylation of proteins involved in lipid signaling (PLDδ), endomembrane trafficking, hormone, light, and receptor signaling, and photosynthesis. Together, our results show that Dw2 modulates endomembrane function and cell division during sorghum internode growth, providing insight into the regulation of monocot stem development. Significance Statement Bioenergy sorghum (Sorghum bicolor L. Moench.) is a promising drought‐tolerant high‐biomass crop that produces 4–5 m stems that account for approximately 80% of harvested biomass. In this study, Dw2, a signaling kinase shown to regulate stem growth, altered the phosphorylation of proteins involved in lipid signaling and endomembrane function and modified endocytosis, internode cell proliferation, vascular bundle anatomy, and the localization of heteroxylan and mixed linkage glucan in cell walls.