Sinorhizobium meliloti-induced chitinase gene expression in Medicago truncatula ecotype R108-1: a comparison between symbiosis-specific class V and defence-related class IV chitinases.
The Medicago truncatula (Gaertn.) ecotypes Jemalong A17 and R108-1 differ in Sinorhizobium meliloti-induced chitinase gene expression. The pathogen-inducible class IV chitinase gene, Mtchit 4, was strongly induced during nodule formation of the ecotype Jemalong A17 with the S. meliloti wild-type strain 1021. In the ecotype R108-1, the S. meliloti wild types Sm1021 and Sm41 did not induce Mtchit 4 expression. On the other hand, expression of the putative class V chitinase gene, Mtchit 5, was found in roots of M. truncatula cv. R108-1 nodulated with either of the rhizobial strains. Mtchit 5 expression was specific for interactions with rhizobia. It was not induced in response to fungal pathogen attack, and not induced in roots colonized with arbuscular mycorrhizal (AM) fungi. Elevated Mtchit 5 gene expression was first detectable in roots forming nodule primordia. In contrast to Mtchit 4, expression of Mtchit 5 was stimulated by purified Nod factors. Conversely, Mtchit 4 expression was strongly elevated in nodules formed with the K-antigen-deficient mutant PP699. Expression levels of Mtchit 5 were similarly increased in nodules formed with PP699 and its parental wild-type strain Sm41. Phylogenetic analysis of the deduced amino acid sequences of Mtchit 5 (calculated molecular weight = 41,810 Da, isoelectric point pH 7.7) and Mtchit 4 (calculated molecular weight 30,527 Da, isoelectric point pH 4.9) revealed that the putative Mtchit 5 chitinase forms a separate clade within class V chitinases of plants, whereas the Mtchit 4 chitinase clusters with pathogen-induced class IV chitinases from other plants. These findings demonstrate that: (i) Rhizobium-induced chitinase gene expression in M. truncatula occurs in a plant ecotype-specific manner, (ii) Mtchit 5 is a putative chitinase gene that is specifically induced by rhizobia, and (iii) rhizobia-specific and defence-related chitinase genes are differentially influenced by rhizobial Nod factors and K antigens.
Salzer
Peter
P
Botanisches Institut der Universität Basel, Hebelstrasse 1, 4056, Switzerland. Peter.Salzer@unibas.ch
Feddermann
Nadja
N
Wiemken
Andres
A
Boller
Thomas
T
Staehelin
Christian
C
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000494:pharmacology; D000954:Antigens, Surface / Q000494:pharmacology; D002688:Chitinases / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D017343:Genes, Plant; D008070:Lipopolysaccharides / Q000494:pharmacology; D029902:Medicago / Q000235:genetics / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012231:Rhizobium / Q000235:genetics; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000235:genetics; D013559:Symbiosis; D013997:Time Factors
D000942:Antigens, Bacterial; D000954:Antigens, Surface; C030659:K antigens; D008070:Lipopolysaccharides; D002688:Chitinases