RESUMEN
Ascorbate peroxidases (APXs) are antioxidant enzymes that play vital roles in redox homeostasis in plants. Citrus is susceptible to infection by Xanthomonas citri subsp. citri (Xcc), resulting in citrus bacterial canker (CBC). The present study used bioinformatic and expression analyses to investigate the APX family in Citrus sinensis. Bioinformatic research revealed the chromosomal locations, phylogeny, gene structure, promoter elements, functional domains, conserved motifs, and most likely physicochemical properties of the sequences. Six APXs clustered in three groups were identified, with each protein containing a single peroxidase domain. The promoter regions contained a variety of transcription factor-binding and hormone-response components. Xcc infection induced different CsAPX01 and CsAPX02 expressions in the CBC-susceptible Wanjincheng and CBC-resistant Kumquat varieties. Subcellular localization and transient expression showed that CsAPX01 and CsAPX02 were expressed in the cytoplasm and nucleus and had hydrogen peroxide (H2O2)-scavenging activity. Virus-induced gene silencing (VIGS) of CsAPX01 and CsAPX02 resulted in strong resistance to CBC and H2O2 bursts without effects on the plant phenotype. The current study focused on investigating and characterizing the citrus APX family. It was found that CsAPX01 and CsAPX02 exacerbated CBC by altering the balance of H2O2. These findings emphasize the importance of APXs in enhancing plant resistance to pathogens.
RESUMEN
MT3 shows apparently different properties and function from MT1 even though they have 70% sequence homology. Possibly the two inserts, Thr5 and a negatively charged hexapeptide at position-55 in MT3, play important roles. A series of MT3 variants around the EAAEAE hexapeptide have been prepared by site-directed mutagenesis and their properties and reactivity towards pH, EDTA and DTNB have been studied. Our detailed studies revealed that the EAAEAE insert is essential to the property of MT3. It is the hexapeptide insert, to some extent, making the MT3 alpha-domain looser and lower stability of the metal-thiolate cluster, which could be accessed more easily.