Phosphotransferase activity of acid phosphatases of a Citrobacter sp.

The acid phosphatase of an atypical Citrobacter sp. was purified in two isoforms, designated CPI and CPII, which had different K_m values for glycerol 1-phosphate and glycerol 2-phosphate The enzyme was not inhibited by the end-product glycerol. Enzyme activity was increased in the presence of phosphate acceptor molecules having free hydroxyl groups (glycerol, methanol, ethanol). ³¹P-nuclear magnetic resonance spectroscopy indicated transfer of the liberated phosphate onto the alcohol, with the de novo production of (e.g.) glycerol 1-phosphate by enzyme supplemented with phosphomonoester substrate and glycerol.     

GhXB38D represses cotton fibre elongation through ubiquitination of ethylene biosynthesis enzymes GhACS4 and GhACO1

Ethylene plays an essential role in the development of cotton fibres. Ethylene biosynthesis in plants is elaborately regulated by the activities of key enzymes, 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS); however, the potential mechanism of post-translational modification of ACO and ACS to control ethylene synthesis in cotton fibres remains unclear. Here, we identify an E3 ubiquitin ligase, GhXB38D, that regulates ethylene biosynthesis during fibre elongation in cotton. GhXB38D gene is highly expressed in cotton fibres during the rapid elongation stage. Suppressing GhXB38D expression in cotton significantly enhanced fibre elongation and length, accompanied by the up-regulation of genes associated with ethylene signalling and fibre elongation. We demonstrated that GhXB38D interacts with the ethylene biosynthesis enzymes GhACS4 and GhACO1 in elongating fibres and specifically mediates their ubiquitination and degradation. The inhibition of GhXB38D gene expression increased the stability of GhACS4 and GhACO1 proteins in cotton fibres and ovules, resulting in an elevated concentration of ethylene. Our findings highlight the role of GhXB38D as a regulator of ethylene synthesis by ubiquitinating ACS4 and ACO1 proteins and modulating their stability. GhXB38D acts as a negative regulator of fibre elongation and serves as a potential target for enhancing cotton fibre yield and quality through gene editing strategy.