Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide.In this study,a two-year field experiment was conducted to investigate the effect of coronatine(COR),a functional analog of jasmonic acid(JA),on maize drought resistance.The experiment included two water treatments(rainfed and irrigation),four COR concentrations(mock,0μmol L^(-1);A1,0.1μmol L^(-1);A2,1μmol L^(-1);A3,10μmol L^(-1))and two maize genotypes(Fumin 985(FM985),a drought-resistant cultivar and Xianyu 335(XY335),a drought-sensitive cultivar).Spraying 1μmol L^(-1)COR at seedling stage increased surface root density and size,including root dry matter by 12.6%,projected root area by 19.0%,average root density by 51.9%,and thus root bleeding sap by 28.2%under drought conditions.COR application also increased leaf area and SPAD values,a result attributed to improvement of the root system and increases in abscisic acid(ABA),JA,and salicylic acid(SA)contents.The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation.COR application reduced anthesis and silking interval,increasing kernel number per ear.COR treatment at 1μmol L^(-1)increased the yield of XY335 and FM985 by 7.9%and 11.0%,respectively.Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area,increasing maize drought resistance mainly via leaf area index and dry matter accumulation.Overall,COR increased maize drought resistance mainly by increasing root dry weight and root area,with 1μmol L-^(-1)COR as an optimal concentration.

Role of Coronatine in Inducing Infection and Improving Resistance to Pseudomonas syringae pv.mori in Mulberry Seedlings

Mulberry bacterial blight is caused by Pseudomonas syringae pv.mori.Coronatine(COR),a phytotoxin and phytohormone produced by several strains of Pseudomonas syringae,is suggested to have an important role in pathogen-plant interaction.The aim of our study was to examine the influence of COR on mulberry in the process of pathogen infection.Results showed that COR could suppress stomatal closure induced by pathogen-associated molecular patterns(PAMPS),assist pathogenic bacteria into the leaves,and promote bacterial proliferation in the tissues.High-concentration(1 μmol/L) exogenous COR and COR-producing bacterial pathogen induced chlorosis symptom and decrease of chlorophyll content,contrary to the effects of low-concentration(0.001 μmol/L) exogenous COR and non-COR-producing bacterial pathogen.Treatments with COR and DC3000 enhanced the production of reactive oxygen species(ROS),namely,hydrogen peroxide(H_2O_2) and superoxide anion(O_2),but there were two H_2O_2 peaks at 1-3 hpi and 8-24 hpi in the DC3000-treated leaves while only one peak at 1-3 h was observed 1-3 h in the COR-treated ones.H_2O_2 could kill the pathogenic bacteria,on the other hand,it also acted as an upstream signaling molecule to promote nitric oxide(NO) production to further participate in the signaling pathway.Enzymatic antioxidant systems(superoxide dismutase,peroxidase and catalase) and defensive enzyme systems(lipoxygenase,polyphenol oxidase and phenylalnine ammonialyase) were activated by COR.Therefore,COR could cooperate on the invasion and proliferation of COR-producing bacterial pathogens,and induce the chlorosis symptom in mulberry.At the same time,exogenously applied COR also could enhance the resistance to P.syringae pv.mori by production of signal molecules to activate signaling pathway and promoting defense-related metabolism.

Coronatine promotes maize water uptake by directly binding to the aquaporin ZmPIP2;5 and enhancing its activity

Water uptake is crucial for crop growth and development and drought stress tolerance. The water channel aquaporins(AQP) play important roles in plant water uptake. Here, we discovered that a jasmonic acid analog, coronatine(COR), enhanced maize(Zea mays) root water uptake capacity under artificial water deficiency conditions. COR treatment induced the expression of the AQP gene Plasma membrane intrinsic protein 2;5(ZmPIP2;5).In vivo and in vitro experiments indicated that COR also directly acts on ZmPIP2;5 to improve water uptake in maize and Xenopus oocytes. The leaf water potential and hydraulic conductivity of roots growing under hyperosmotic conditions were higher in ZmPIP2;5-overexpression lines and lower in the zmpip2;5 knockout mutant, compared to wild-type plants. Based on a comparison between ZmPIP2;5 and other PIP2s, we predicted that COR may bind to the functional site in loop E of ZmPIP2;5. We confirmed this prediction by surface plasmon resonance technology and a microscale thermophoresis assay, and showed that deleting the binding motif greatly reduced COR binding. We identified the N241 residue as the COR-specific binding site, which may activate the channel of the AQP tetramer and increase water transport activity,which may facilitate water uptake under hyperosmotic stress.