Mycorrhiza stimulates root-hair growth and IAA synthesis and transport in trifoliate orange under drought stress

Abstract

Root-hair growth and development regulated by soil microbes is associated with auxin. In this background, we hypothesized that mycorrhizal fungal inoculation induces greater root-hair growth through stimulated auxin synthesis and transport under water stress conditions. Trifoliate orange (Poncirus trifoliata) was inoculated with an arbuscular mycorrhizal (AM) fungus (Funneliformis mosseae) under well-watered (WW) and drought stress (DS) for 9 weeks. Compared with non-AM seedlings, AM seedlings displayed significantly higher density, length, and diameter of root hairs and root indoleacetic acid (IAA) level, whereas lower total root IAA efflux, regardless of soil moisture status. Root PtYUC3 and PtYUC8 involved in IAA biosynthesis were up-regulated by mycorrhization under WW and DS, whereas AM-modulated expression in PtTAA1, PtTAR2, PtYUC4, and PtYUC6 depended on status of soil moisture. Mycorrhizal inoculation down-regulated the transcript level of root auxin efflux carriers like PtPIN1 and PtPIN3, whereas significantly up-regulated the expression of root auxin-species influx carriers like PtABCB19 and PtLAX2 under DS. These results indicated that AMF-stimulated greater root-hair growth of trifoliate orange under DS that is independent on AMF species is related with mycorrhiza-modulated auxin synthesis and transport, which benefits the host plant to enhance drought tolerance.

Effects of Arbuscular Mycorrhizal Fungi on Growth and Physiological Performance of Catalpa bungei C.A.Mey. under Drought Stress

“…Our results indicated that inoculation with AMF considerably augmented IAA (with the exception of MD stress) and GA 3 levels, but reduced zeatin (ZT, a cytokinin) in the leaves of C. bungei seedlings, exposed either to WW or drought stress conditions. This is in accordance with previous findings [22,66,99]. It implies that AMF could postpone leaf senescence and cause a quick adaptation to drought stress by influencing the auxin signal transduction.…”

Benefits of Arbuscular Mycorrhizal Fungi Application to Crop Production under Water Scarcity

“…Similarly, stimulation of biosynthesis and transport of IAA in roots of trifoliate orange under water restrictions were demonstrated [97]. Under drought conditions, AM colonization overexpressed PtYUC3 and PtYUC8 involved in IAA biosynthesis, and downregulated auxin efflux carriers (PtPIN1 and PtPIN3), while up-regulated auxin-species influx carriers (PtABCB19 and PtLAX2) in roots, leading to significantly higher IAA accumulation in mycorrhizal roots versus non-AM roots [97]. Together with higher IAA, colonized trifoliate orange plants showed a significant increase in MeJA, nitric oxide, and calmodulin in roots, supporting greater root adaptation of morphology as a crucial strategy for drought adaptation [93].…”

“…In a recent study, an increased content of indole-3-acetic acid (IAA) which is the dominant naturally occurring auxin was found in mycorrhizal tomato plants exposed to drought [91]. Similarly, stimulation of biosynthesis and transport of IAA in roots of trifoliate orange under water restrictions were demonstrated [97]. Under drought conditions, AM colonization overexpressed PtYUC3 and PtYUC8 involved in IAA biosynthesis, and downregulated auxin efflux carriers (PtPIN1 and PtPIN3), while up-regulated auxin-species influx carriers (PtABCB19 and PtLAX2) in roots, leading to significantly higher IAA accumulation in mycorrhizal roots versus non-AM roots [97].…”

Isolation and Properties of Enterobacter sp. LX3 Capable of Producing Indoleacetic Acid

“…Paenibacillus polymyxa could be developed to control pathogens and increase crop yield by producing IAA in field applications [6]. Additionally, inoculation of Funneliformis mosseae with trifoliate orange resulted in greater root-hair growth in density, length and diameter of seedling roots [7]. Overproduction of IAA improved nitrogen-fixing performances of endophytic microbes in culture or inoculated host plants [8].…”