Transcriptomic analyses reveal clathrin-mediated endocytosis involved in symbiotic seed germination of Gastrodia elata.

Gastrodia elata is a well-known medicinal orchid. In nature, the germination rate of G. elata is extremely poor, because there is no endosperm within the mature seed. It is crucial for G. elata to obtain nutrition from mycorrhizal fungi (Mycena) at the early-stage of germination. After germination, the seed gives rise to a protocorm. However, there are no "omic" studies on understanding the interaction between Gastrodia and Mycena. Here, we used transcriptomic approaches to explore changes in seed germination of G. elata. Based on RNA-Seq, a total of ~221 million clean reads were assembled denovo into 139,756 unigenes, including 42,140 unigenes that were annotated in public databases. Meanwhile, 1750 unigenes were identified as differentially expressed genes. Most of these differentially expressed genes were putatively involved in energy metabolism, plant defense, molecular signaling, and secondary metabolism. Additionally, numerous genes involved in clathrin-mediated endocytosis were identified from our data. Most of these genes (e.g., clathrin, adaptor protein, dynamin, HSC70) were basally expressed in seeds and highly expressed in protocorms. Our data suggested that clathrin-mediated endocytosis could play important roles in symbiotic seed germination of G. elata with Mycena infections.