Gastrodia elata Blume is commonly called Tian ma in Chinese and is primarily distributed in mountainous areas of East Asia, Southeast Asia and Oceania (Ahn, Jeon, Lim, Jung, & Park, 2007; Chen, Ji, & Zhu, 1999; Liu et al., 2015; Tang & Eisenbrand, 1992; Zhan et al., 2016). Modern pharmacological experiments have demonstrated that extracts of G. elata or its active compounds possess wide-reaching biological activities, including antitumor, anti-virus, memory-improving, antioxidation and anti-aging actions (Heo et al., 2007; Hu & Shen, 2014; Huang & Wang, 1985). As a perennial, non-photosynthetic orchid, G. elata needs to establish a symbiotic relationship with Armillaria strains at late stages to obtain nutrients and energy (Chen et al., 2020; Lan & Li, 1994; Wang, Yang, Zeng, & Hu, 2007; Zou, Bai, Lv, Xu, & Sun, 2010). The species of genus Armillaria were well known as phytopathogens that caused serious root rot disease on natural forests, tree plantations for timber production, orchards, vineyards, and gardens (Heinzelmann et al., 2019; Koch, Wilson, Sense, Henkel, & Aime, 2017; Labbé et al., 2017; Onsando, Wargo, & Waudo, 1997). However, several species of Armillaria had been identified to be able to form symbiont with G. elata (Cha & Igarashi, 1995; Cha & Igarashi, 1996; Guo, Wang, Xue, Zhao, & Yang, 2016; Sekizaki et al., 2008), and affect both the yields and the quality of the tubers of Tian ma (Guo et al., 2016).
It has been known for many years that phytohormones and their signaling network play a central role on the regulation of plant growth and development during plant life cycle, recent research revealed that these signaling pathways are probably present in nonplant species (Bari & Jones, 2009; Grant & Jones, 2009). Various microbes can produce or affect the phytohormones levels of their hosts, furthermore, auxins, cytokinins(CKs), GAs, abscisic acid (ABA) and ethylene (ET) had been isolated from microbial fermentation (Chanclud & Morel, 2016; R. Eichmann et al., 2021; Ludwig-Müller, 2015). On the other side, many works disclosed that host hormones played an important role in plant-microbe interaction. IAA had been proved to be able to induced production of invasive filaments in Saccharomyces cerevisiae (Prusty et al., 2004), and increased the antimicrobial activity of Streptomycetaceae strains isolated from Arabidopsis roots (van der Meij et al., 2018). CKs improves the progression of fungal biotrophic pathogens and stimulate beneficial AMF interactions in pea (Chanclud & Morel, 2016). Exogenous ABA induced vast gene expression changes in the endophyte Aspergillus nidulans (Xu, Yang, Meng, & Wang, 2018). GAs inhibits the nodulation and AMF formation, while BRs seem to support it (Foo, Mcadam, Weller, & Reid, 2016; Foo, Ross, Jones, & Reid, 2013).
Historically, GA was primarily known as a prominent type of phytohormone that regulate many aspects of plant development and physiology (de Lucas et al., 2008; Olszewski, Sun, & Gubler, 2002). Although GAs biosynthesis by fungi has been documented and reviewed, few research focused on the signaling pathways of GAs in fungi (Hedden, 2020). Through transcriptome analysis and phytohormone quantification, Takeda et al. revealed the accumulation of GA in Japanese lotus root lines infected with AM fungi, indicating the importance of de novo synthesis of GA in arbuscular mycorrhizal development (Takeda et al., 2015). It was reported that exogenous GA3 significantly increased hyphopodium formation at the epidermis, thus leading to the promotion of fungal colonization and arbuscule formation in the root cortex (Tominaga et al., 2020). Furthermore, GAs could promote the germination of conidia and the growth of the mycelium of Neurospora crassa (Barker & Tagu, 2000). However, no specific studies have been carried out at the transcriptome level to clarify the responses of Armillaria starin to GA3 and how they relate to the symbiotic relationships.
Some research works have investigated the mechanisms of its symbiotic relationship with G. elata (Li, Guo, & Lee, 2020; Tsai et al., 2016). Yuan et al. observed that the strigolactone, as a phytohormone, could promote the branching and development of Armillaria mellea hyphae (Yuan et al., 2018). However, there is still limited knowledge on the symbiotic molecular mechanism between the Armillaria strain and G. elata. In previous works, we sequenced the genome of A. gallica 012m isolated from the tuber of G. elata collected from a plantation field, and investigated the symbiotic relationship with G. elata (Zhan et al., 2020). During the experiment, we found that the vegetative mycelium of A. gallica 012m grew significantly better in the media containing GA3 than the control. The experimental phenomenon implied us that GA3 might be an important signal molecule for A. gallica 012m. Here, we show the genome-guided analysis of differential expression between additional GA3 and BK. These studies provide a foundation to characterize GA3 signaling in A. gallica 012m.