FBW7 targets KLF10 for ubiquitin-dependent degradation.

FBW7, a key component of SCFFBW7 E3 ubiquitin ligase, targets various proteins for degradation via the conserved Cdc4 phosphodegron (CPD) in substrates. In this study, we report that KLF10 is degraded by FBW7 via a conserved CPD. Through systematic analysis of the degradation of KLF transcription factors by FBW7, we identified KLF10 as a novel degradation target of FBW7. Ectopic expression of FBW7 markedly promoted the degradation of KLF10 while knockdown of endogenous FBW7 increased the protein levels of KLF10. In addition, simultaneous mutations of both threonine 82 (T82) and serine 86 (S86) significantly reduced the FBW7-mediated KLF10 degradation. Moreover, KLF10 containing a conserved putative CPD (TPPXSP) from amino acids 82 to 87, directly interacted with WD40 domain of FBW7 in a phosphorylation-dependent manner. Importantly, FBW7 could reverse the KLF10-mediated inhibition of Smad7 activity. Thus, our study uncovers a novel regulatory mechanism underlying which KLF10 stability and its biological function are mediated by FBW7.

Isolation and characterization of a catalase gene "HuCAT3" from pitaya (Hylocereus undatus) and its expression under abiotic stress.

Abiotic stresses usually cause H2O2 accumulation, with harmful effects, in plants. Catalase may play a key protective role in plant cells by detoxifying this excess H2O2. Pitaya (Hylocereus undatus) shows broad ecological adaptation due to its high tolerance to abiotic stresses, e.g. drought, heat and poor soil. However, involvement of the pitaya catalase gene (HuCAT) in tolerance to abiotic stresses is unknown. In the present study, a full-length HuCAT3 cDNA (1870 bp) was isolated from pitaya based on our previous microarray data and RACE method. The cDNA sequence and deduced amino acid sequence shared 73-77% and 75-80% identity with other plant catalases, respectively. HuCAT3 contains conserved catalase family domain and catalytic sites. Pairwise comparison and phylogenetic analysis indicated that HuCAT3 is most similar to Eriobotrya japonica CAT, followed by Dimocarpus longan CAT and Nicotiana tabacum CAT1. Expression profile analysis demonstrated that HuCAT3 is mainly expressed in green cotyledons and mature stems, and was regulated by H2O2, drought, cold and salt stress, whereas, its expression patterns and maximum expression levels varied with stress types. HuCAT activity increased as exposure to the tested stresses, and the fluctuation of HuCAT activity was consistent with HuCAT3 mRNA abundance (except for 0.5 days upon drought stress). HuCAT3 mRNA elevations and HuCAT activities changes under cold stress were also in conformity with the cold tolerances among the four genotypes. The obtained results confirmed a major role of HuCAT3 in abiotic stress response of pitaya. This may prove useful in understanding pitaya's high tolerance to abiotic stresses at molecular level.