Growth ofArabidopsisseedlings on high fungal doses ofPiriformospora indicahas little effect on plant performance, stress, and defense gene expression in spite of elevated jasmonic acid and jasmonic acid-isoleucine levels in the roots

Abstract

The endophytic fungus Piriformospora indica colonizes the roots of many plant species including Arabidopsis and promotes their performance, biomass, and seed production as well as resistance against biotic and abiotic stress. Imbalances in the symbiotic interaction such as uncontrolled fungal growth result in the loss of benefits for the plants and activation of defense responses against the microbe. We exposed Arabidopsis seedlings to a dense hyphal lawn of P. indica. The seedlings continue to grow, accumulate normal amounts of chlorophyll, and the photosynthetic parameters demonstrate that they perform well. In spite of high fungal doses around the roots, the fungal material inside the roots was not significantly higher when compared with roots that live in a beneficial symbiosis with P. indica. Fifteen defense- and stress-related genes including PR2, PR3, PAL2, and ERF1 are only moderately upregulated in the roots on the fungal lawn, and the seedlings did not accumulate H2O2/radical oxygen species. However, accumulation of anthocyanin in P. indica-exposed seedlings indicates stress symptoms. Furthermore, the jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile) levels were increased in the roots, and consequently PDF1.2 and a newly characterized gene for a 2-oxoglurate and Fe2+-dependent oxygenase were upregulated more than 7-fold on the dense fungal lawn, in a JAR1- and EIN3-dependent manner. We conclude that growth of A. thaliana seedlings on high fungal doses of P. indica has little effect on the overall performance of the plants although elevated JA and JA-Ile levels in the roots induce a mild stress or defense response.

Arabidopsis thalianaroot colonization by the nematophagous fungusPochonia chlamydosporiais modulated by jasmonate signaling and leads to accelerated flowering and improved yield

“…Overcolonized plants looked healthy without any symptom beyond growth limitation (not shown). A very similar situation has been described for the association between A. thaliana and a typical mutualist such as P. indica (Vahabi et al ., ). Indeed, beneficial endophytes including P. indica have been suggested to maintain a behavior that is closer to that of biotrophic fungi (Lahrmann et al ., ), which typically evoke SA signaling.…”

Colonization by the endophyte Piriformospora indica leads to early flowering in Arabidopsis thaliana likely by triggering gibberellin biosynthesis

“…nutrient uptake and promotes plant growth [19,20], confers drought tolerance to Arabidopsis and barley [21,22], and alleviates salt stress in barley and rice by increasing the activity of detoxifying enzymes and the content of photosynthetic pigments in colonized plants [16,23]. Recently, P indica has been shown to promote inflorescence development leading to early flowering in the medicinal plant Coleus forskohill [18].…”

The endophytic fungus Piriformospora indica enhances Arabidopsis thaliana growth and modulates Na + /K + homeostasis under salt stress conditions

“…The symbiosis between P. indica and roots of colonized plants has been shown to improve plant tolerance to different abiotic and biotic stresses [36]. P. indica has been reported to alter plant specialized metabolites, increase nutrient uptake, and promote plant growth [37,38]. In addition, P. indica improves drought tolerance to Arabidopsis and barley [39,40] and was shown to alleviate salt stress in barley and rice by increasing the activity of detoxifying enzymes and photosynthetic pigment content in colonized plants [41,42].…”