The Medicago truncatula hydrolase MtCHIT5b degrades Nod factors of Sinorhizobium meliloti and cooperates with MtNFH1 to regulate the nodule symbiosis.

Nod factors secreted by nitrogen-fixing rhizobia are lipo-chitooligosaccharidic signals required for establishment of the nodule symbiosis with legumes. In , the Nod factor hydrolase 1 (MtNFH1) was found to cleave Nod factors of . Here, we report that the class V chitinase MtCHIT5b of expressed in can release lipodisaccharides from Nod factors. Analysis of mutant plants indicated that MtCHIT5b, together with MtNFH1, degrades Nod factors in the rhizosphere. expression was induced by treatment of roots with purified Nod factors or inoculation with rhizobia. MtCHIT5b with a fluorescent tag was detected in the infection pocket of root hairs. Nodulation of a knockout mutant was not significantly altered whereas overexpression of resulted in fewer nodules. Reduced nodulation was observed when and were simultaneously silenced in RNA interference experiments. Overall, this study shows that nodule formation of is regulated by a second Nod factor cleaving hydrolase in addition to MtNFH1.