SCPL48 regulates the vessel cell programmed cell death during xylem development in Arabidopsis thaliana

Secondary cell wall (SCW) deposition is tightly coordinated with programmed cell death (PCD) during xylem development and plays a crucial role in plant stress responses. In this study, we characterized a serine carboxypeptidase-like gene, SCPL48, which exhibits xylem cell-specific expression patterns in stem xylem during vascular development. The scpl48 plants exhibited reduced stem xylem cell numbers, particularly vessel cells, accompanied by delayed organelle degradation during PCD and increased secondary wall thickness in xylem vessel cells. In contrast, SCPL48 overexpression resulted in increased vessel cell abundance and accelerated degradation of vessel cell contents, suggesting its critical role in xylem vessel cell differentiation. Notably, SCPL48 expression was significantly up-regulated in response to ABA treatment and drought stress, with SCPL48 overexpression lines demonstrating enhanced drought resistance. Further molecular analyses revealed that SCPL48 was directly targeted and transcriptionally activated by key SCW regulators VND6, and MYB46. Furthermore, the expression of PCD-related protease genes, including XCP1, XSP1, RNS3, MC9, γVPE, and CEP1, showed compensatory changes in both scpl48 mutants and SCPL48 overexpression lines. Collectively, our findings demonstrate that SCPL48 functions as a key regulator in xylem vessel cell differentiation, PCD and drought stress responses.