Abstract
Endophytes have the ability to improve plant nutrition alongside their agronomic performance, among which arbuscular mycorrhizal fungi provide the most benefits to their host. Previously, we reported for the first time that an arbuscular mycorrhizal-like fungus
Piriformospora indica
had the ability to colonize roots of trifoliate orange (
Poncirus trifoliata
) and conferred positive effects on nutrient acquisition. Present study showed the changes in fatty acids and sugars to unravel the physiological and symbiotic association of trifoliate orange with
P
.
indica
and an arbuscular mycorrhizal fungus,
Funneliformis mosseae
singly or in combination. All the endophytic fungi collectively increased fructose, glucose, and sucrose content in leaves and roots, along with a relatively higher increase with
P
.
indica
inoculation than with
F
.
mosseae
alone or dual inoculation. Treatment with
P
.
indica
increased the concentration of part unsaturated fatty acids such as C18:3N6, C20:2, C20:3N6, C20:4N6, C20:3N3, C20:5N3, C22:1N9, and C24:1. Additionally,
P
.
indica
induced the increase in the concentration of part saturated fatty acids such as C6:0, C8:0, C13:0, C14:0, and C24:0.
F
.
mosseae
hardly changed the content of fatty acids, except for increase in C14:0 and C20:5N3. Double inoculation only reduced the C21:0, C10:0, C12:0, C18:3N3, and C18:1 content and increased the C20:5N3 content. These endophytic fungi up-regulated the root
PtFAD2, PtFAD6, PtΔ9
, and
PtΔ15
gene expression level, coupled with a higher expression of
PtFAD2
and
PtΔ9
by
P
.
indica
than by
F
.
mosseae
. It was concluded that
P
.
indica
exhibited a stronger response, for sugars and fatty acids, than
F
.
mosseae
on trifoliate orange. Such results also reveal the
Pi
(an
in vitro
culturable fungus) as a bio-stimulator applying to citriculture.