Cloning And Analysis Of Metalloprotease Genes And A Pathogenesis-related Gene In S.surattense

Proteolytic enzymes are intricately involved in many aspects of plant physiology and development. Peptidases constitute of 1-5% of the gene content. In terms of both structure and function, metalloproteases are the most diverse of proteases. Recently researches on plant organellar metalloproteases have intrigued great interest in their potential functions. Here we reported on isolating, identifying and characterizing three novel cDNAs, namely Sszn-mp1, Sszn-mp2 and Sszn-mp3, from Solarium surattense. To identify the intracellular location, genomic organization, mature protein forms, structures and functions of these three isolated new cDNAs from S. surattense, integrated approaches were used. In this study, 9 Zn-MPs deduced or assembled from other plant species and six Zn-MPs from cyanobacteria in the GenBank database were used. Being specific to the plant and cyanobacterium kingdom and related to photosynthesis, the plant Zn-MP members shared more than 62% overall identity with SsZn-MP3 and the six cyanobacterium putative proteases had about 20% identity with SsZn-MP3 in which some residues and regions were highly conserved. Southern blot and genomic analyses revealed that there is probably only one or two copies of zn-mp in the genome and the mature mRNAs coding the Zn-MPs could be accurately spliced with seven or less extrons in plants. The plant zn-mp genes encoding membrane proteins are potentially targeted to chloroplast, endoplasmic reticulum (membrane) and plasma membrane, and the bacterium Zn-MPs to the cytoplasmic membrane. Sszn-mps expressed differently in tissues and regulated by various stimuli. Western blot analyses showed that only SsZn-MP1 exists as a membrane protein in S. surattense, the highly conserved family members could form different forms of mature proteins in plants, and these proteins will be cleaved off their N-terminal targeting peptide. Analyses revealed that these proteins belongs to a novel conserved membrane zinc metalloprotease (Zn-MP) family. The Zn-MP proteins contained a conserved zinc binding site (HEAGHX19E/DX46-48EX7EGG), a potential G-protein coupled receptor (GPCR) family 1 signature and a triplet motif ( the N-R/K-F motif in plant Zn-MPs and the D/E-R-Y/T motif in the six bacterium Zn-MPs), suggesting that the different mature forms of Zn-MPs may function as proteases or / and signal receptors. This study provides a basis for further investigating the biochemical and physiological functions of the new metalloprotease family in the future.