The involvement of a cysteine proteinase in the nodule development in Chinese milk vetch infected with Mesohizobium huakuii subsp rengei

Cys proteinases play important roles in plant cell development and senescen ce. A cDNA, AsNODf32, obtained by differential screening of a nodule cDNA l ibrary of the leguminous plant Chinese milk vetch (Astragalus sinicus), rep resents a nodule-specific Cps proteinase similar to that reported for the a ctinorhizal Alnus glutinosa-Flankin symbiosis. A characteristic feature of this proteinase is the presence of a putative vacuolar targetting signal, L QDA, within its propeptide. Expression of the AsNODf32 gene, which was stud ied on northern blots and in situ hybridization, showed good correlation wi th the onset of nodule senescence. In situ hybridization studies revealed t hat AsNODf32 was expressed in senescent-infected tissue at the base of the nodule, as well as in interzone II-III of the infected nodules. In addition to degrading old nodule tissues and bacteroids, AsNODf32 protein may be re quired as a component of tissue remodeling during nodule development.