Arabidopsis DELLA Protein Degradation Is Controlled by a Type-One Protein Phosphatase, TOPP4

Abstract

Gibberellins (GAs) are a class of important phytohormones regulating a variety of physiological processes during normal plant growth and development. One of the major events during GA-mediated growth is the degradation of DELLA proteins, key negative regulators of GA signaling pathway. The stability of DELLA proteins is thought to be controlled by protein phosphorylation and dephosphorylation. Up to date, no phosphatase involved in this process has been identified. We have identified a dwarfed dominant-negative Arabidopsis mutant, named topp4-1. Reduced expression of TOPP4 using an artificial microRNA strategy also resulted in a dwarfed phenotype. Genetic and biochemical analyses indicated that TOPP4 regulates GA signal transduction mainly via promoting DELLA protein degradation. The severely dwarfed topp4-1 phenotypes were partially rescued by the DELLA deficient mutants rga-t2 and gai-t6, suggesting that the DELLA proteins RGA and GAI are required for the biological function of TOPP4. Both RGA and GAI were greatly accumulated in topp4-1 but significantly decreased in 35S-TOPP4 transgenic plants compared to wild-type plants. Further analyses demonstrated that TOPP4 is able to directly bind and dephosphorylate RGA and GAI, confirming that the TOPP4-controlled phosphorylation status of DELLAs is associated with their stability. These studies provide direct evidence for a crucial role of protein dephosphorylation mediated by TOPP4 in the GA signaling pathway.

TYPE-ONE PROTEIN PHOSPHATASE4 Regulates Pavement Cell Interdigitation by Modulating PIN-FORMED1 Polarity and Trafficking in Arabidopsis

“…In addition, two transfer DNA insertion lines of TOPP4, SALK_090980, and N466328 did not show any obvious PC defects (Qin et al, 2014;Supplemental Fig. S6), possibly due to the high expression level of TOPP4 in these two lines or functional redundancy among TOPP genes.…”

“…In our previous work, we identified a severely dwarfed dominant-negative mutant topp4-1 and found that TOPP4 acts as a positive regulator in GA signaling through dephosphorylating DELLA proteins (Qin et al, 2014). The topp4-1 mutant was also found to show PC defects.…”

“…To confirm whether the single nucleotide substitution in TOPP4 is responsible for the defective PC phenotype, we observed four independent 35S:TOPP4 topp4-1 T1-transformed lines (Qin et al, 2014). Three lines (complement [COM] 1#-COM 3#) showed a completely recovered PC phenotype (Fig.…”

“…Therefore, it appeared that the recovery effect on PCs was positively correlated with the expression level of TOPP4 gene in topp4-1. We also analyzed PC morphology of five individual TOPP4: TOPP4 topp4-1-transformed lines (Qin et al, 2014). They all showed a slightly recovered PC phenotype (two lines are showed in Supplemental Fig.…”

The number of cell types, information content, and the evolution of complex multicellularity

“…Plants and animals use small molecules for inter-cellular signaling that are transduced by binding to disorder-containing receptor proteins, and PONDR VSL2b [45] and other disorder predictors indicate that the various plant homeodomain-containing transcription factors contain significant amounts of disorder, and they undergo PTM [46]. For example, rice KNOX undergoes tissue-specific AS [47], whereas DELLA proteins are phosphorylated for degradation [48].…”