Pathogenesis and defense gene response in Crocus sativus (saffron) against the root-lesion nematode Pratylenchus...

Crocus sativus (saffron) gains its global reputation due to presence of unique apocarotenoids such as crocin, picrocrocin and safranal. However, due to its limited geographic distribution and various abiotic and biotic stresses, saffron is facing significant loss in production and quality. Among biotic stresses, plant parasitic nematodes remain unexplored so far. This study was carried out to investigate pathogenic potential of the root-lesion nematode, Pratylenchus penetrans and the defense gene response of C. sativus. The P. penetrans parasitism resulted in the production of a smaller number of flowers with delayed time required for flower emergence. The nematode parasitism also affected stigma length and weight. Crocin, the major apocarotenoid in saffron, was significantly reduced in flowers arising from nematode parasitized corms. A down-regulation was also observed for some apocarotenoid pathway genes such as phytoene synthase, lycopene β-cyclase and carotenoid cleavage dioxygenase 2, the key biosynthetic enzymes for crocin biosynthesis. To understand the molecular interactions between C. sativus and P. penetrans, we performed RNA-seq of control and nematode parasitized corms identifying 1316 significantly differentially expressed genes (DEGs). Gene ontology and pathway enrichment analyses showed that genes associated with plant signaling, stress response and secondary metabolism were among these DEGs. Phenylpropanoid pathway genes were predominantly expressed in response to the nematode attack. Some genes uniquely associated with plant defense were differentially up-regulated in response to parasitism including NOI1, ILITYHIA, JOKA2, LIFEGUARD 4, and SAWADEE HOMEODOMAIN HOMOLOG. These findings may deepen our understanding on the saffron-nematode interactions.