Mp. Goettingminesky et Bc. Mullin, DIFFERENTIAL GENE-EXPRESSION IN AN ACTINORHIZAL SYMBIOSIS - EVIDENCE FOR A NODULE-SPECIFIC CYSTEINE PROTEINASE, Proceedings of the National Academy of Sciences of the United Statesof America, 91(21), 1994, pp. 9891-9895
Nodules formed on the roots of actinorhizal plants as a consequence of
nitrogen-fixing symbioses with the actinomycete Frankia appear to res
ult from modification of the developmental pathway that leads to later
al root formation. Presently no information exists about factors that
control, this developmental switch or, until now, about genes that are
differentially expressed as a result of an altered developmental path
way. Differential screening of an Alnus glutinosa nodule cDNA library
revealed altered levels of gene expression in nodules as compared with
roots and allowed isolation of host plant nodule-specific cDNA sequen
ces. The deduced amino acid sequence of one full-length cDNA, AgNOD-CP
1, represents a nodule-specific cysteine proteinase similar to cystein
e proteinases of the papain superfamily. Residues critical to catalysi
s, active site, and disulfide bridges are conserved. Suggested roles f
or this enzyme are as a defense response to Frankia invasion, as a com
ponent of tissue remodeling in root and nodule tissues, as a cell cycl
e component, or as an element of protein turnover. Complexity of hybri
dization patterns revealed by Southern blot analysis suggests that the
gene for AgNOD-CP1 is a member of a multigene family, Northern hybrid
ization results indicate that this gene may have been recruited for a
role specific to this symbiosis, a phenomenon observed in the Rhizobiu
m-legume symbioses, perhaps common to many microbe-plant interactions.