The Vital Role of ShTHIC from the Endophyte OsiSh-2 in Thiamine Biosynthesis and Blast Resistance in the OsiSh-2-Rice Symbiont

Abstract

Endophytes can benefit the growth and stress resistance of host plants by secreting bioactive components. Thiamine is an essential vitamin involved in many metabolic pathways and can only be synthesized by microbes and plants. In this study, we found that thiamine could inhibit the development of the phytopathogen Magnaporthe oryzae and decrease the rice blast index under field conditions. In the thiamine biosynthesis pathway, the key enzyme ShTHIC of an endophyte Streptomyces hygroscopicus OsiSh-2 and OsTHIC of rice (Oryza sativa) were highly homologous. Gene overexpression or knockout approaches revealed that both THIC contributed to thiamine synthesis and resistance to M. oryzae. Furthermore, S. hygroscopicus OsiSh-2 colonization led to a decrease in the thiamine synthesis level of rice but still maintained thiamine homeostasis in rice. However, inoculation with the ShTHIC knockout strain ΔTHIC reduced the thiamine content in rice, although the thiamine synthesis level of rice was increased. After infection with M. oryzae, blast resistance was dramatically improved in OsiSh-2-inoculated rice but decreased in ΔTHIC-inoculated rice compared with non-inoculated rice. This result demonstrated that ShTHIC could regulate thiamine biosynthesis and consequently assist blast resistance in the OsiSh-2-rice symbiont. Our results revealed a novel blast-resistance mechanism mediated by a key thiamine biosynthetic enzyme from an endophyte OsiSh-2.

Ferroptosis induction in host rice by endophyte OsiSh-2 is necessary for mutualism and disease resistance in symbiosis

“…For M. oryzae punch inoculation assays. Rice leaf inoculation assays were performed following a previously described method 68 . Briefly, detached leaves of four-week-old rice were lightly wounded with a mouse ear punch, and then 6 μl of M. oryzae spore suspension (concentration of 5 × 10 5 conidia/mL in 0.02% Tween-20) was applied to the wounded leaves.…”

“…To investigate the antagonism of OsiSh-2 (WT) and Δ cchH against M. oryzae , a dual-culture assay was performed 68 . Briefly, M. oryzae was inoculated in the centre of the PDA plate, and the strains were streaked one line 30 mm above the centre.…”

“…Plasmid construction and intergeneric conjugation between Escherichia coli and Streptomyces were performed as described previously 68 . Briefly, the plasmid pYH7- cchH was introduced into the wild-type strain OsiSh-2, with the helper plasmid pUZ8002 in E. coli ET12567 through conjugation on the MS agar plates.…”

The Rice Endophyte-Derived α-Mannosidase ShAM1 Degrades Host Cell Walls To Activate DAMP-Triggered Immunity against Disease

“…In our previous study, we found that the rice endophyte Streptomyces hygroscopicus OsiSh-2 and its cell-free culture filtrate (CFC) had strong antagonistic activity against M. oryzae via the action of nigericin and siderophores ( 3 , 29 ). OsiSh-2 could regulate thiamine biosynthesis and thus assist in blast resistance in the OsiSh-2-rice symbiont ( 30 ). Specifically, OsiSh-2 also has ISR activity in rice for resisting M. oryzae , including induction of a priming response ( 31 ).…”