Abstract

A wide range of biological processes are regulated by sumoylation, a post-translational modification involving the conjugation of SUMO (Small Ubiquitin-Like Modifier) to protein. In Arabidopsis thaliana , AtSIZ1 encodes a SUMO E3 ligase for SUMO modification. siz1 mutants displayed defective secondary cell walls (SCWs) in inflorescence fiber cells. Such defects were caused by repression of SND1/NST1 -mediated transcriptional networks. Yeast two-hybrid assay indicated that SIZ1 interacts with the LBD30 C-terminal domain, which was further confirmed using bimolecular fluorescence complementation and immunoprecipitation. Mass spectrometry and co-immunoprecipitation indicated that SIZ1 mediates SUMO conjugation to LBD30 at the K226 residue. Genes controlling SCW formation were activated by the overexpression of LBD30 , but not in the LBD30 ( K226R ) mutant. LBD30 enhancement of SCW formation resulted from upregulation of SND1/NST1 -mediated transcriptional networks. This study presents a mechanism by which sumoylation of LBD30, mediated by SIZ1, regulates SCW formation in A . thaliana . Secondary cell wall (SCW) is essential for upright plant growth and long-distance transport of water and solutes. Regulation of SCW formation at the transcriptional level has been much studied. Here we show that AtSIZ1, a small ubiquitin-related modifier (SUMO) E3 ligase, mediates the sumoylation of transcription factor LBD30, a process that regulates SCW formation. Elucidating a role of sumoylation in the post-translational regulation of SCW formation, complementing the body of research on regulation at the transcriptional level, provides additional insight into a key process that is essential for upright growth and the long-distance transport of water and solutes in plants.