RNase T2 genes from rice and the evolution of secretory ribonucleases in plants.
The plant RNase T2 family is divided into two different subfamilies. S-RNases are involved in rejection of self-pollen during the establishment of self-incompatibility in three plant families. S-like RNases, on the other hand, are not involved in self-incompatibility, and although gene expression studies point to a role in plant defense and phosphate recycling, their biological roles are less well understood. Although S-RNases have been subjects of many phylogenetic studies, few have included an extensive analysis of S-like RNases, and genome-wide analyses to determine the number of S-like RNases in fully sequenced plant genomes are missing. We characterized the eight RNase T2 genes present in the Oryza sativa genome; and we also identified the full complement of RNase T2 genes present in other fully sequenced plant genomes. Phylogenetics and gene expression analyses identified two classes among the S-like RNase subfamily. Class I genes show tissue specificity and stress regulation. Inactivation of RNase activity has occurred repeatedly throughout evolution. On the other hand, Class II seems to have conserved more ancestral characteristics; and, unlike other S-like RNases, genes in this class are conserved in all plant species analyzed and most are constitutively expressed. Our results suggest that gene duplication resulted in high diversification of Class I genes. Many of these genes are differentially expressed in response to stress, and we propose that protein characteristics, such as the increase in basic residues can have a defense role independent of RNase activity. On the other hand, constitutive expression and phylogenetic conservation suggest that Class II S-like RNases may have a housekeeping role.
MacIntosh
Gustavo C
GC
Interdepartmental Genetics Program, Iowa State University, 2214 Molecular Biology Bldg., Ames, IA 50011, USA. gustavo@iastate.edu
Hillwig
Melissa S
MS
Meyer
Alexander
A
Flagel
Lex
L
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004722:Endoribonucleases / Q000737:chemistry / Q000235:genetics*; D019143:Evolution, Molecular; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D007527:Isoenzymes / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010802:Phylogeny; D016415:Sequence Alignment
D007527:Isoenzymes; D004722:Endoribonucleases; C022543:ribonuclease T(2)