The Polyketides and Sesquiterpenes for Enhancing Plant Resistance from Endophyte Nigrospora lacticolonia

Sixteen new secondary metabolites, including one unprecedented 2-butylresorcinol-ketone hybrid (1) with 6/6/5/6 tetra-cyclic benzannulated spiroketal scaffold, two xyloketal analogues 2 and 3 with an unique 5,6-dihydro-2H-pyran-2-one residue, one caryophyllene sesquiterpene (4), three C₁₀ polyketides (6, 7, 9), four γ-lactone derivatives (12, 14-16), one unusual botryodiplodin-hydroxy ketone hybrid (17), and four unusual C₁₀ polyketide-botryodiplodin hybrids (19-22) were isolated from Paris polyphylla endophyte, Nigrospora lacticolonia. Their structures were identified mainly by NMR, ECD, and X-ray crystallography. The biosynthetic pathway of 1 was proposed. Compounds 6-8, 12, 17, 19, and 21 demonstrated significant antiphytopathogenic activities against Fusarium oxysporum, comparable to nystatin. Most compounds exhibited growth-promoting effects on rice seeds under F. oxysporum, salinity, and cold stresses. At 100 μg/mL, compounds 3 and 16 exhibited insecticidal activities with mortality rates of 55.0% and 48.3%, respectively. Significantly, compound 3 showed plant resistance against phytopathogens, salt stress, and insecticidal activity. The structure-activity relationship was also discussed.