长枝木霉代谢物对极细链格孢产毒抑制机制解析

邵学辉,张树武*,徐秉良*

(甘肃农业大学植物保护学院·甘肃省农作物病虫害生物防治工程实验室,兰州 730070)

摘 要:【目的】明确长枝木霉(SC5)代谢粗提物对极细链格孢(ABL2)产毒抑制机制。【方法】以富士苹果的叶片为供试材料,通过生长速率法、LC-MS和RT-qPCR技术测定了SC5代谢粗提物对ABL2菌落生长、6种非寄主选择性毒素产生及产毒相关基因表达的抑制作用。【结果】质量浓度为0.5 mg∙mL-1的SC5代谢粗提物对ABL2菌落生长和致病力具有显著的抑制作用,第6天时抑制率分别为38.08%和76.96%;同时,0.5 mg∙mL-1 SC5代谢粗提物对ABL2菌株产生的非寄主选择性毒素TEN、ALT和TeA均具有显著抑制作用,其中处理2 d后对毒素的抑制作用最显著,其含量分别降低69.39%、98.51%和48.99%,并且其合成相关基因TESTES(1)、PksAPksJ 的表达量显著下调,分别降低89.02%、98.20%、46.49%和40.13%,但是对ABL2菌株非寄主选择性毒素ATX-Ⅰ含量和参与编码其合成的PksF基因表达量具有提升作用。【结论】质量浓度为0.5 mg∙mL-1的SC5代谢粗提物对ABL2菌株生长和致病力具有抑制作用,可能通过调控ABL2菌株TESTES(1)、PksAPksJ基因下调表达,进而降低TEN、ALT和TeA的毒素的产生量及致病力。

关键词:苹果叶片;极细链格孢;长枝木霉;毒素;基因表达;生物防治

植物病原链格孢(Alternaria spp.)引起的苹果病害,在世界各大产区普遍发生[1]。如苹果链格孢专化型(A. alternata f.sp. mail)引起的苹果斑点落叶病,主要危害苹果叶片,使叶部出现褐色病斑,最终导致提前落叶[2]。同时,也可危害嫩枝和果实,导致树势衰弱,影响花芽形成和果实正常生长[3]。但是,近年来笔者课题组在甘肃省苹果产区首次发现由极细链格孢(A.tenuissima)引起的苹果叶枯病,发生后严重导致苹果叶片枯死脱落。据报道,链格孢菌可通过产生链格孢毒素危害植物。已发现的链格孢毒素可分为5 类,分别为二苯-α-吡喃酮类及其衍生物、苝醌类及其衍生物、四氨基酸及其衍生物、长链氨基多元醇的丙三羧酸酯类化合物、混杂多样结构[4-5]。目前,研究最多的链格孢毒素有交链孢酚(AOH:Alternariol)、交链孢单甲醚(AME:Alternariol monomethyl ether)、交链孢烯(ALT:Altenuene)、交链孢毒素(ATX-Ⅰ、Ⅱ、Ⅲ:Altertoxin)、腾毒素(TEN:Tentoxin)、细交链孢菌酮酸(TeA:Tenuazonic Acid),其不仅对植物产生严重危害[6-7],而且危及农产品食品安全[8-9]。同时,相关研究发现链格孢毒素的生物合成受相关基因调控。Wenderoth 等[10]鉴定了AOH、AME生物合成相关的基因簇PksIomtImoxIaohRsdrIdoxI并确定其功能;Liu等[11]发现聚酮合酶基因Pks参与链格孢代谢途径且参与次生代谢物的合成,进而影响链格孢毒素含量;Li等[12]研究发现和验证了TESTES(1)基因是链格孢合成TEN毒素所需的两个基因簇。目前,化学防治依旧是防控链格孢属真菌引起的病害的主要手段[13],但是长期大量使用可导致链格孢菌抗药性产生和污染环境[14],因此,寻找一类对链格孢具有较好防治效果的生防制剂对该病害的防控具有重要意义。

木霉作为一种优良的生防菌,被广泛应用于农业生产中的病害防治[15]。前期Abdel-Lateff 等[16]从长枝木霉代谢物中分离出一种吡喃酮衍生物,发现其具有清除自由基、抗氧化、抑菌活性;Mironenka等[17]发现哈茨木霉(Trichoderma harzianum)代谢物可抑制黄色镰孢菌产孢,同时减少其色素和主要毒素的含量。但是,目前有关木霉代谢物对极细链格孢产毒抑制机制尚未见报道。因此,笔者在本试验中评价了长枝木霉代谢粗提物对极细链格孢的抑菌效果和毒素产生的影响,旨在为防治链格孢引起的苹果叶枯病提供参考依据和理论基础。

1 材料和方法

1.1 材料

1.1.1 供试菌株 极细链格孢(A.tenuissima)ABL2(序列号:MZ222271)和长枝木霉(T. longibrachiatum)SC5(序列号:ON786721)菌株由甘肃农业大学植物保护学院植物病毒学和分子生物学实验室分离、鉴定并保存。

1.1.2 供试叶片 供试叶片采自甘肃农业大学苹果种植园,品种为富士。

1.1.3 标准溶液与试剂 链格孢毒素标准溶液(AOH、AME、ALT、TEN、TeA、ATX-Ⅰ)购自青岛普瑞邦生物工程有限公司;乙酸乙酯(分析纯)、甲酸(色谱纯)、乙醇(分析纯)、甲醇(色谱纯)和乙腈(色谱纯)均购自天津市大茂化学试剂厂;TRNzol Universal 总RNA 提取试剂购自TⅠANGEN 公司;cDNA 合成试剂盒、RT-qPCR 试剂盒和DNA Marker 均购自TaKaRa Bio 公司;上下游引物由北京擎科生物科技有限公司西安分公司合成。

1.2 方法

1.2.1 长枝木霉SC5 和极细链格孢ABL2 菌株活化 将低温保存的SC5 和ABL2 菌株分别接种于PDA 培养基活化培养7 d 后,并再次制取菌饼接种于新的PDA培养基活化备用。

1.2.2 长枝木霉SC5代谢粗提物制备 SC5代谢粗提物制备参照Liu 等[18]的方法并稍作修改。利用无菌打孔器制取活化3 d 且直径为5 mm 的SC5 菌饼,并接种于200 mL PDB培养基(3个菌饼),然后置于光照、28 ℃、150 r∙min-1的恒温振荡培养箱中振荡培养。待培养15 d 后,利用中速定性滤纸抽滤去除菌丝,并将滤液经4 ℃、10 000 r∙min-1离心30 min 后,利用3倍体积的乙酸乙酯充分振荡并萃取。将乙酸乙酯相置于旋转蒸发仪蒸干浓缩并经1 mL 甲醇溶解和0.22 μm滤器过滤,再次浓缩获得SC5代谢粗提物。

1.2.3 长枝木霉SC5 代谢粗提物对极细链格孢ABL2 生长的抑制作用 将浓缩后的SC5 代谢粗提物利用甲醇配制质量浓度为200 mg∙mL-1母液。同时,分别取1.000、0.500、0.250、0.125、0.050、0.025 和0.005 mL的母液用甲醇制成1 mL的工作液,并加入99 mL 灭菌后待凝固的PDA 中,制得含SC5 代谢粗提物质量浓度为2.00、1.00、0.50、0.25、0.10、0.05 和0.01 mg∙mL-1含药培养基,以加入1 mL甲醇的培养基作为对照。然后,将直径为5 mm的ABL2菌饼接种于不同浓度含药培养基中央,并置于温度为25 ℃全光照培养箱中培养,每个处理和对照均设10次重复,分别在接种培养第2、4、6、8和10 d时,采用十字交叉法测量菌落直径,并计算SC5 代谢粗提物对ABL2生长抑制率。

1.2.4 长枝木霉SC5 代谢粗提物对极细链格孢ABL2致病力的影响 将1.2.3中经不同浓度SC5代谢粗提物和甲醇处理培养6 d 时的ABL2 菌株作为供试处理菌株和对照菌株,参照Desrochers 等[19]的方法提取ABL2 菌株代谢产物,并测定其致病力。利用直径为7 mm 打孔器制取5 个不同浓度处理菌株和对照菌株菌饼,并分别置于10 mL EP 管中,每个处理3 次重复。然后,分别加入8 mL 乙酸乙酯,并经涡旋振荡和超声提取后离心(8000 r∙min-1)去除菌饼、菌丝。待静置1 h 后将乙酸乙酯相置于旋转蒸发仪蒸干浓缩并经1 mL 甲醇溶解和0.22 μm滤器过滤,收集获得不同浓度处理菌株和对照菌株代谢产物。然后,将无菌滤纸片(直径5 mm)置于不同浓度处理菌株和对照菌株代谢产物浸泡1 h,制备含有ABL2 代谢产物的滤纸片备用。利用75%乙醇将健康的苹果叶片消毒后,经无菌水清洗3 次,然后,利用吸水纸吸干叶片表面水分,采用针刺接种法刺破叶片表面,并将含有不同浓度处理菌株和对照菌株ABL2 代谢产物(阳性对照)的滤纸片接种于刺伤部位,试验以1 mL 甲醇浸泡等时间的滤纸片作为阴性对照,每组5 个重复。接种后置于人工气候箱,于第5 天时利用十字交叉法测量其病斑大小。

1.2.5 长枝木霉SC5 代谢粗提物对极细链格孢ABL2 毒素含量的影响 将SC5 代谢粗提物对ABL2 菌落和致病力抑制最佳浓度作为供试浓度,测定SC5代谢粗提物对ABL2毒素含量的影响。试验以1.2.3 中SC5 代谢粗提物对ABL2 菌落生长抑制作用最佳浓度培养基培养的ABL2 菌株作为处理,并以加入等体积甲醇的培养基培养的ABL2 菌株作为对照,分别于培养2、4、6、8 和10 d 后制备处理和对照的菌饼,并参考1.2.4方法提取和制备处理和对照菌株代谢产物。待制备获得处理和对照菌株代谢产物后,利用LC-MS 检测其AOH、AME、ALT、TEN、TeA和ATX-Ⅰ含量。试验利用甲醇作为溶剂配制不同质量浓度(1000、500、250、100、50、25、10、5和1 ng ∙mL-1)链格孢毒素AOH、AME、ALT、TEN、TeA 和ATX-Ⅰ标准品的混标溶液,并利用LC-MS 测定后制作标准曲线(图1、表1)。

表1 标准品信息及标准曲线
Table 1 Standard information and standard curve

毒素Toxins ALT AOH TeA TEN ATX-ⅠAME分子式Compounds C15H16O6 C14H10O5 C10H15NO3 C22H30N4O4 C20H16O6 C15H12O5加合物Adducts[M+H]+[M+H]+[M+H]+[M+H]+[M+H]+[M+H]+时间Time/min 2.765 3.125 3.102 3.053 3.132 4.115回归方程Standard curve Y=64.467 733X+30.958 680 Y=2.547 454X+11.387 593 Y=2.764 007X+2.815 021 Y=65.262 738X+30.167 858 Y=0.200 634X+1.828 624 Y=2.371 551X+13.451 023拟合度R2 0.999 8 0.999 4 0.999 9 0.999 9 0.999 9 0.999 8

图1 链格孢毒素标准品定性、定量离子质谱图
Fig.1 Qualitative and quantitative ion mass spectrometry of alternaria toxin standard

A、B 和C 及对应数字分别为定性离子、定量离子和母离子及其质荷比。
A,B and C and the corresponding numbers are qualitative ions,quantitative ions and parent ions and their mass-to-charge ratios,respectively.

然后,利用LC-MS检测处理和对照菌株代谢产物AOH、AME、ALT、TEN、TeA和ATX-Ⅰ含量。超高效液相色谱条件为:Agilent 1290超高效液相色谱仪配备Elipse Plus C18(规格1.8 μm,2.1 mm×150 mm)色谱柱;柱温设置为30 ℃;流动相A为0.2%的甲酸水,B 为加入0.2%氨水的乙腈;进样量为5 μL;流速设置0.3 mL∙min-1(表2);质谱条件为:Agilent 6460三重四级杆质谱检测器配备电喷雾离子源,采用正离子模式(ESⅠ+);扫描范围(m∙z-1)设置为100~900;锥孔电压分别设置为80、95 eV:碰撞电压为15、25、35 eV;NMR数据监测模式;锥孔气流150 L∙h-1;离子源温度350 ℃;喷雾电压7500 V(表3)。同时,利用Agilent MassHunter Quantitative Analysis(For QQQ)分析并计算处理和对照菌株代谢产物AOH、AME、ALT、TEN、TeA和ATX-Ⅰ含量。

表2 色谱洗脱梯度
Table 2 Chromatographic elution gradients.

时间Time/min 0.00 1.00 4.00 5.00 7.00组分A Fraction A/%95 45 15 95 95组分B Fraction B/%5 55 85 55流速Flow/(mL∙min-1)0.3 0.3 0.3 0.3 0.3

表3 质谱参数
Table 3 Mass spectrometry parameters.

毒素Toxins ALT AOH TeA TEN ATX-ⅠAME母离子Parention 293.1 259.1 198.1 415.2 353.1 273.1碎片离子Daughterion 275.1/257.0 212.9/185.1 124.8/82.9 358.2/312.2 299.1/270.9 230.0/212.1锥孔电压Cone voltage/eV 80 95 80 95 80 95碰撞电压Collision voltage/eV 5/15 25/35 15/25 15/15 35/35 35/35

1.2.6 长枝木霉SC5 代谢粗提物对极细链格孢ABL2 毒素合成相关基因表达的影响(1)样品采集及总RNA 的提取和cDNA 第一链合成。将SC5代谢粗提物对ABL2菌落和致病力抑制最佳浓度作为供试浓度,测定SC5 代谢粗提物对ABL2 毒素合成相关基因表达的影响。试验以1.2.3 中SC5 代谢粗提物对ABL2菌落生长抑制作用最佳浓度培养基培养的ABL2 菌株作为处理,并以加入等体积甲醇的培养基培养的ABL2 菌株作为对照,待处理2、4、6、8 和10 d 后收集处理和对照ABL2 菌株菌丝。菌丝处理方法参照郑朋飞等[20]的,将处理和对照菌丝置于液氮中并充分研磨破碎,每个处理和对照均3个重复。然后,根据TRNzol Universal 总RNA 提取试剂说明书提取RNA,并进行浓度及A260/A280 比值测定。利用PrimeScript™RT reagent Kit (Perfect Real Time)试剂盒进行反转录,合成处理和对照样品cDNA第一链。

(2)ABL2 毒素合成相关基因表达量分析。试验以处理2、4、6、8 和10 d 后的处理和对照ABL2 菌株菌丝cDNA 第一链为模板,利用TB Green® Premix Ex Taq™(Tli RNaseH Plus)试剂盒测定SC5 代谢粗提物对ABL2 毒素合成相关基因[PksJPksAPksI、PksF、TESTES1)]表达的影响,以BenA 作为内参基因,并利用2-∆∆Ct法计算其相对表达量。利用Primer 5软件设计引物,引物序列见表4。

表4 引物信息
Table 4 Primer information

基因Gene PksJ PksA PksI PksF TES TES(1)BenA基因编号Gene ⅠD ATN-PG05411 ATN-PG11581 ATN-PG01857 ATN-PG07778 KT947104 KT947105 MK558218.1上游引物Forward primer(5’-3’)GTCCCAAATTCCTACCCTCAC CGGTCTATCTCGTCCCTCAA TGGCATACGGGTAAGGTCTA CCTTCTTGTCGCCTACTTCAG CTGATAGCCGAGCACTCCAG CCGGACGACATGATGCAATG GTTGAGAACTCAGACGAGACCTTCTGCATTG下游引物Reverse primer(3’-5’)GATAGCCATCGAAAGCATTCCC CGGCGTGCTGTAGTAGTGTAG CGTGACGCTCTGGATAGTTC AACTCCATCGCATCCTCCAA TCGGATAAGGCGTTACGTCG ATCGATCCGTCGCTGTTCAA GAACCATGTTGACGGCCAACTTCCTC

1.3 数据处理

采用MS office Excel 2021 和ⅠBM SPSS Statistics 27 软件对数据进行统计分析,并运用Duncan’s新复极差法进行多重比较,利用OriginPro 2021作图并分析。

2 结果与分析

2.1 长枝木霉SC5代谢粗提物对极细链格孢ABL2生长的抑制作用

SC5 代谢粗提物对ABL2 菌落的抑制作用随着代谢粗提物浓度的增加而逐渐增强(图2)。与对照(图2-A)相比,经质量浓度为2.00、1.00、0.50、0.25、0.10、0.05和0.01 mg∙mL-1的SC5代谢粗提物处理6 d的ABL2 菌落直径显著小于对照(图2-B~H),且不同质量浓度之间存在显著差异。如表5 所示,当培养2 d时,质量浓度为2 mg∙mL-1的SC5代谢粗提物对ABL2菌落生长抑制率达到最大值,为90.42%,当SC5 代谢粗提物质量浓度大于0.05 mg∙mL-1时,随着培养时间的增加,抑制率趋于平稳。

表5 不同时间和浓度SC5 代谢粗提物处理后的ABL2 菌落生长抑制率
Table 5 Different time and concentration of SC5 metabolic crude extract on ABL2 colony growth inhibition rate %

注:不同小写字母表示ABL2 经SC5 代谢粗提物处理不同时间后致病力差异显著(p<0.05)。
Note:Different small letters indicate that the pathogenicity of ABL2 was significantly different at different times after treatment with SC5 metabolic crude extract at p<0.05.

ρ/(mg∙mL-1)2.00 1.00 0.50 0.25 0.10 0.05 0.01时间Time/d 2 90.42±1.51 a 83.56±2.88 a 59.98±8.61 a 28.21±8.65 a 55.76±6.98 a 4.07±3.55 d 9.54±5.61 a 10 74.92±0.98 e 69.82±0.98 d 34.77±1.81 c 31.63±2.17 a 34.15±1.92 c 38.89±1.80 a 6.04±2.46 ab 4 6 8 86.67±1.04 b 78.01±1.22 b 47.96±3.16 b 28.05±4.07 a 43.78±2.62 b 8.15±2.96 d 8.09±4.30 a 81.30±1.58 c 72.66±2.51 c 38.08±3.45 c 31.21±3.92 a 33.20±6.87 c 17.37±9.16 c 4.16±2.17 b 77.67±1.21 d 70.78±1.22 d 35.77±1.60 c 30.27±0.96 a 33.86±1.04 c 23.08±1.53 b 6.62±2.27 ab

图2 不同浓度SC5 代谢粗提物对ABL2 菌落生长的抑制效果
Fig.2 The inhibitory effect of different concentrations of SC5 metabolic crude extracts on the growth of ABL2 colonies

图片分别表示对照、2.00、1.00、0.50、0.25、0.10、0.05 和0.01 mg∙mL-1 SC5 代谢粗提物处理ABL2 菌株6 d 时的菌落形态。
The pictures represent the colony morphology of ABL2 strain treated with control,2.00,1.00,0.50,0.25,0.10,0.05 and 0.01 mg∙mL-1 SC5 metabolic crude extract for 6 days.

2.2 长枝木霉SC5代谢粗提物对极细链格孢ABL2致病力的影响

结果如图3 所示,经不同浓度的SC5 代谢粗提物处理后的ABL2 代谢产物致病力随着浓度的增加而减弱。接种叶片5 d 后,经质量浓度为0.01~0.25 mg ∙mL-1(图3-A、B)SC5 代谢粗提物处理后的ABL2 代谢产物的致病力呈降低趋势,与其他处理相比,经质量浓度为0.50~2.00 mg ∙mL-1(图3-A、B)SC5 代谢粗提物处理后的ABL2 代谢产物致病力显著降低,与阳性对照相比分别降低了76.96%、81.94%和80.95%。

图3 SC5 代谢粗提物对ABL2 代谢产物致病力的影响
Fig.3 The effect of SC5 metabolites on the pathogenicity of ABL2 metabolites

A 和B 分别表示叶片致病形态特征和病斑直径。B 中CK1 和CK2 分别表示阴性和阳性对照。不同小写字母表示ABL2 经不同浓度SC5 代谢粗提物处理后致病力差异显著(p<0.05)。
A and B represent the pathogenic morphological characteristics and lesion diameter of leaves.CK1 and CK2 in B represent negative and positive controls.Different small letters indicated that the pathogenicity of ABL2 was significantly different after treatment with different concentrations of SC5 metabolic crude extracts at p<0.05.

2.3 长枝木霉SC5代谢粗提物对极细链格孢ABL2毒素产生的影响

结果表明(图4),SC5代谢粗提物对ABL2菌株ALT、AME、AOH、TeA、ATX-Ⅰ和TEN毒素含量具有显著的影响,并且不同时间段的毒素含量存在明显差异。与对照相比,处理2~8 d 后,SC5 代谢粗提物对ABL2 菌株ALT(图4-A)和TEN(图4-D)毒素含量具有显著的抑制作用,其处理时间段内平均含量分别较对照降低59.74%和84.41%。然而,处理2~8 d后,SC5 代谢粗提物对ABL2 菌株AME(图4-B)、AOH(图4-C)、TeA(图4-E)和ATX-Ⅰ(图4-F)毒素含量具有不同程度的影响,其中在处理2 d后均表现出一定的抑制作用,但是随着处理时间的增加,其抑制作用不显著,与对照相比,处理时间段内TeA含量整体呈降低趋势,ATX-Ⅰ含量整体呈上升趋势,AOH和AME含量在处理6~8 d时显著高于对照。

图4 SC5 代谢粗提物对ABL2 毒素产生的影响
Fig.4 Effect of crude extract of SC5 on toxin content of ABL2

不同小写字母表示ABL2 经SC5 代谢粗提物处理同一时间后毒素含量差异显著(p<0.05)。下同。
Different small letters indicated that the toxin content of ABL2 was significantly different after treatment with SC5 metabolic crude extract for different time at p<0.05.The same below.

2.4 产毒相关基因表达分析

结果表明(图5),SC5代谢粗提物对ABL2菌株产毒相关基因TESTES(1)、PksJPksAPksFPksI表达具有显著的影响,并且不同时间段的表达存在显著差异。与对照相比,处理2~10 d,SC5代谢粗提物对ABL2菌株TES(图5-A)、TES(1)(图5-B)、PksA(图5-D)和PksI(图5-F)基因表达量具有显著的抑制作用,其处理时间段内平均表达量较对照降低了61.35%、65.83%、56.94%和65.19%。然而,处理2~10 d,SC5 代谢粗提物对ABL2 菌株PksJ(图5-C)和PksF(图5-E)基因表达量具有不同程度的影响,其中在处理2~4 d 时对PksF 表现出一定的抑制作用,但随着处理时间的增加,抑制作用变为促进作用,而在处理2~8 d 时对PksJ 表现出一定的抑制作用,但在处理10 d后却由抑制变为促进。

图5 SC5 代谢粗提物对ABL2 产毒相关基因的影响
Fig.5 Effects of crude extract of SC5 on toxin-related genes of ABL2

3 讨 论

Liu 等[11]发现链格孢代谢途径中与毒素合成相关的聚酮合酶Pks 基因会受到肉桂醛的抑制;Yun等[21]证明TAS1 可催化异亮氨酸和乙酰辅酶合成TeA;Saha 等[22]研究发现PksJ 下调会直接抑制AOH和AME 的合成,PksBPksI 的下调并不直接影响AOH 和AME 的合成,而PksH 则通过调节PksJPksI 的表达来控制AOH和AME的合成。Li等[12]研究发现两个分别编码一个非核糖体合成酶和一种细胞色素P450蛋白的基因TESTES(1),并进一步验证TESTES(1)参与Tentoxin 合成。目前,利用长枝木霉代谢粗提物抑制极细链格孢产毒的研究尚未报道。笔者在本研究中发现0.5 mg∙mL-1的SC5 代谢粗提物对ABL2菌落生长和代谢产物的致病力有较好的抑制效果,并通过抑制产毒相关基因的表达减少毒素含量。通过分析基因表达量和毒素含量后发现随着培养时间的增加PksJ表达量呈下调趋势,同时TeA 含量呈下降趋势,且在第2 天、第4 天和第6 天时显著低于对照,但在第10 天时PksJ 表达量高于对照,同时TeA含量也高于对照,表明TeA的合成主要受PksJ调控,这与Liu等[11]的研究结果一致;而PksA 的表达量先上升后下降,在第6 天时达到最大值,但均显著低于对照,这与TEN 毒素含量的变化趋势相同,初步推测PksA参与了TEN毒素的生物合成,同时PksI表达量也随时间的增加呈上调趋势,但显著低于对照,且AOH 和AME 含量随时间变化呈上升趋势,在第6天和第8天时却显著高于对照,表明PksAPksI共同参与AOH和AME的生物合成,且PksA 在第6 天时开始参与调控TEN 毒素的生物合成,这与Liu 等[11]的研究结果一致,但与Saha 等[22]的研究结果略有差异,初步判断差异的原因是抑菌物质和致病菌的不同;TESTES(1)表达量与对照相比显著降低,同时TEN含量(ρ)在第6天达到最大值8.74 ng ∙mL-1,说明TESTES(1)主要参与调控TEN 的生物合成,这与Li 等[12]等的研究结果相同;ATX-Ⅰ含量呈上升趋势,在第4天、第6天、第8天和第10 天时均显著高于对照,这与PksF 表达情况相似,同时ALT 含量呈上升趋势且显著低于对照,这与PksI 表达情况相似,但PksFPksI 如何调控ATX-Ⅰ和ALT 的生物合成还有待研究。结果表明,SC5 代谢粗提物在0.5 mg∙mL-1的质量浓度下会抑制ABL2 菌落的生长和非寄主选择性毒素TEN、ALT和TeA的生物合成,从而减少毒素含量,但有关SC5代谢粗提物抑制ABL2菌株毒素合成及其相关基因表达的分子作用机制有待深入研究。

4 结 论

(1)筛选获得了长枝木霉SC5 代谢粗体物对极细链格孢ABL2菌株生长抑制作用及其代谢物质致病作用最佳质量浓度为0.5 mg∙mL-1,处理6 d后,其对ABL2菌落生长和致病力抑制率分别为38.08%和76.96%。

(2)初步推测SC5 代谢粗提物抑制ABL2 菌株产毒的机制可能通过抑制ABL2菌株生长同时抑制其产毒相关基因如TESTES1)、PksAPksJ 基因的表达,进而降低ALT、TEN 和TeA 毒素含量,削弱ABL2菌株致病力。

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Identification and mechanism of Trichoderma longibrachiatum metabolites in inhibiting the Alternaria tenuissima toxin production

SHAO Xuehui,ZHANG Shuwu*,XU Bingliang*

(College of Plant Protection,Gansu Agricultural University/Engineering Laboratory for Biological Control of Crop Diseases and Pests,Lanzhou,730070,Gansu,China)

Abstract:【Objective】Alternaria spp.can cause a variety of apple leaf diseases,which occur in all major apple producing areas in the world.Ⅰt can lead to brown disease spots in apple leaves and even result in early defoliation,which seriously affects the development of apple industry and causes huge economic losses.Apple leaf blight caused by Alternaria tenuissima was found for the first time in apple producing areas of Gansu province.This fungus can damage apple leaves and petioles, causing leaves to die and fall off.A. alternata mainly damages plants by producing Alternaria toxins.The Alternaria toxins that have been found can be divided into five categories, i. e, diphenyl-α-pyrones and their derivatives,perylenequinones and their derivatives,tetraamino acids and their derivatives,long-chain amino polyols of glycerol tricarboxylate compounds, and hybrid structures.All of them have obvious toxicity, which can cause serious harm to plants and endanger the food safety of agricultural products.At present,chemical control is still the main means to prevent and control the diseases caused by Alternaria fungi.However,due to the influence of Alternaria resistance and environmental pollution,it is of great significance to find a series of biocontrol agents with higher controlling effect on Alternaria.Biocontrol of Trichoderma is safer and greener than the traditional chemical control methods. Trichoderma metabolites are also good antifungal substances, with broad-spectrum and efficient antibacterial activity, inhibiting the growth and metabolism of pathogenic fungi.The growth and metabolism of A. tenuissima ABL2 strain were inhibited by Trichoderma longibrachiatum SC5 metabolites.The content of non-host selective toxins in the metabolites of A. tenuissima ABL2 strain and the relative expression of genes related to the synthesis of A.tenuissima toxin were determined.The inhibition mechanism of T.longibrachiatum SC5 metabolites on A. tenuissima ABL2 strain production was clarified.The aim was to provide a reference and theoretical basis for the prevention and control of apple leaf blight caused by A.tenuissima.【Methods】T.longibrachiatum SC5 and A.tenuissima ABL2 strains were cultured on PDA medium for 7 days.The PDB liquid medium was made,and the SC5 strain was cultured on the medium for 15 days.The fermentation broth was filtered with filter paper and the broth was retained.The liquid was added with 3-fold-volume-ethyl acetate and oscillated for 1 hour.After standing extraction, the organic phase was evaporated in a rotary evaporator, and 1 ml of methanol was added to dissolve and evaporate.The SC5 metabolites were made into an orginal liquid with a concentration of 200.00 mg∙mL-1,and added to the PDA medium to make a drug-containing medium with different concentrations of SC5 metabolites(0.01,0.05,0.10,0.25,0.50,1.00 and 2.00 mg∙mL-1).The ABL2 strain was inoculated on the drug-containing medium and cultured for 24 hours in a light incubator.The diameter of ABL2 colonies was measured and the colony inhibition rate was calculated on the 2,4,6,8 and 10 days by cross method.On the 6th day,5 mycelial plugs were prepared with a sterile puncher and placed in a 10 mL of EP tube,with 3 replicates per concentration.After adding 8 mL of ethyl acetate,ultrasonic oscillation was performed for 1.5 hours, centrifuged and filtered.After the ethyl acetate phase was evaporated to dryness, 1 mL of methanol was added to dissolve it,and 5 mm circular sterile filter paper was placed in it for later use.Ⅰnoculate healthy leaves after disinfection and rinsing using stab inoculation method.A circular filter paper soaked in ABL2 metabolites was placed at each wound,and placed in an artificial climate box for moisturizing culture for 7 days.The lesion size was measured and the pathogenic activity of the metabolites was calculated.The optimal inhibitory concentration of SC5 metabolites on the growth of ABL2 strain was screened.The total RNA and the metabolites of ABL2 strain growing in the optimal concentration of drug-containing medium was extracted on 2,4,6,8 and 10 days,and the quantitative standard curves of six non-host-selective toxins were made respectively.Six toxin-producing related gene primers were designed and verified for specificity.Liquid Chromatograph Mass Spectrometer and Real Time Quantitative PCR were used to determine the content of toxins in ABL2 metabolites and the relative expression of toxin-producing related genes.【Results】The crude extract of SC5 metabolism at a concentration of 0.5 mg∙mL-1 had a significant inhibitory effect on the growth and pathogenicity of ABL2,and the inhibition rates were 38.08%and 76.96%on the 6th day,respectively.0.5 mg∙mL-1 SC5 metabolic crude extract had a significant inhibitory effect on the non-host selective toxins TEN,ALT and TeA produced by ABL2 strain.The inhibitory effect was the most significant after 2 days treatment, and its content was reduced by 69.39%,98.51%and 48.99%,respectively.The expression levels of TES,TES(1),PksA and PksJ were significantly down-regulated by 89.02%,98.20%,46.49%and 40.13%,respectively.However, the content of non-host selective toxin ATX-Ⅰof ABL2 strain and the expression of PksF gene involved in its synthesis increased.【Conclusion】The SC5 metabolites of T.longibrachiatum at a concentration of 0.5 mg∙mL-1 had an inhibitory effect on the growth and pathogenicity of A.tenuissima ABL2 strain.Ⅰt could reduce and inhibit the content of TEN,ALT and TeA by down-regulating the expression of TES, TES (1), PksA and PksJ genes in ABL2 strain, thereby reducing its pathogenicity.This study can provide a theoretical basis for the biological control of ABL2 strain.

Key words: Fuji apple leaves; Alternaria tenuissima; Trichoderma longibrachiatum; Toxin; Gene expression;Biological control

中图分类号:S661.1 S436.661

文献标志码:A

文章编号:1009-9980(2024)01-0133-10

DOⅠ:10.13925/j.cnki.gsxb.20230369

收稿日期2023-09-15

接受日期:2023-11-23

基金项目甘肃省重点研发计划项目(23YFNA0020);甘肃省科技重大专项(22ZD6NA045);甘肃农业大学“伏羲杰出人才培育计划”项目(Gaufx-03J03);兰州市科技计划项目(2021-1-39)

作者简介邵学辉,男,在读硕士研究生,研究方向为资源利用与植物保护。E-mail:1030372086@qq.com

*通信作者Author for correspondence.E-mail:xubl@gsau.edu.cn;E-mail:zhangsw704@126.com