Integrated transcriptome and metabolite profiling highlights the role of benzoxazinoids in wheat resistance against Fusarium crown rot

Fusarium crown rot(FCR), caused by Fusarium spp., is a chronic and severe plant disease worldwide. In the last years, the incidence and severity of FCR in China has increased to the point that it is now considered a threat to local wheat crops. In this study, for the first time, the metabolites and transcripts responsive to FCR infection in the partial resistant wheat cultivar 04 Zhong 36(04 z36) and susceptible cultivar Xinmai 26(XM) were investigated and compared at 20 and 25 days post inoculation(dpi). A total of 443 metabolites were detected, of which 102 were significantly changed because of pathogen colonization.Most of these 102 metabolites belonged to the flavonoid, phenolic acid, amino acid and derivative classes.Some metabolites, such as proline betaine, lauric acid, ribitol, and arabitol, were stably induced by Fusarium pseudograminearum(Fp) infection at two time points and may have important roles in FCR resistance. In line with the reduced seedling height of 04 z36 and XM plants, RNA-seq analysis revealed that FCR infection significantly affected the photosynthesis activities in two cultivars. Furthermore, 15 jasmonate ZIM-domain genes(JAZ) in the significantly enriched ‘regulation of jasmonic acid mediated signaling pathway’ in 04 z36 were down-regulated. The down-regulation of these JAZ genes in 04 z36 may cause a strong activation of the jasmonate signaling pathway. Based on combined data from gene expression and metabolite profiles, two metabolites, benzoxazolin-2-one(BOA) and 6-methoxy-benzoxazolin-2-one(MBOA), involved in the benzoxazinoid-biosynthesis pathway, were tested for their effects on FCR resistance. Both BOA and MBOA significantly reduced fungal growth in vitro and in vivo, and, thus, a higher content of BOA and MBOA in 04 z36 may contribute to FCR resistance. Above all, the current analysis extends our understanding of the molecular mechanisms of FCR resistance/susceptibility in wheat and will benefit further efforts for the genetic improvement of disease resistance.

Salicylic acid positively regulates maize defenses against lepidopteran insects

In response to insect attack,plants use intricate signaling pathways,including phytohormones,such as jasmonate(JA),ethylene(ET),and salicylic acid(SA),to activate defenses.Maize(Zea mays)is one of the most important staple food crops around the world.Previous studies have shown that the JA and ET signaling play important roles in maize defense against insects,but little is known about whether and how SA regulates maize resistance to insect herbivores.In this study,we ectopically expressed the NahG(salicylate hydroxylase)gene in maize plants(NahG maize)to block the accumulation of SA.It was found that compared with the wild-type(WT)maize,the NahG-maize exhibited decreased resistance to the generalist insects Spodoptera litura and Spodoptera frugiperda and the specialist Mythimna separata,and the compromised resistance in the NahG maize was associated with decreased levels of defensive metabolites benzoxazinoids(Bxs)and chlorogenic acid(CA).Quantification of simulated S.litura feedinginduced JA,JA-isoleucine conjugate(JA-Ile),and ET in the WT and NahG maize indicated that SA does not regulate JA or JA-Ile,but positively controls ET.We provide evidence suggesting that the SA pathway does not crosstalk with the JA or the ET signaling in regulating the accumulation of Bxs and CA.Transcriptome analysis revealed that the bHLH,ERF,and WRKY transcription factors might be involved in SAregulated defenses.This study uncovers a novel and important phytohormone pathway in maize defense against lepidopterous larvae.

Horizontal transfer and evolution of the biosynthetic gene cluster for benzoxazinoids in plants

Benzoxazinoids are a class of protective and allelopathic plant secondary metabolites that have been identified in multiple grass species and are encoded by the Bx biosynthetic gene cluster(BGC)in maize.Data mining of 41 high-quality grass genomes identified complete Bx clusters(containing genes Bx1–Bx5 and Bx8)in three genera(Zea,Echinochloa,and Dichanthelium)of Panicoideae and partial clusters in Triticeae.The Bx cluster probably originated from gene duplication and chromosomal translocation of native homologs of Bx genes.An ancient Bx cluster that included additional Bx genes(e.g.,Bx6)is presumed to have been present in ancestral Panicoideae.The ancient Bx cluster was putatively gained by the Triticeae ancestor via horizontal transfer(HT)from the ancestral Panicoideae and later separated into multiple segments on different chromosomes.Bx6 appears to have been under less constrained selection compared with the Bx cluster during the evolution of Panicoideae,as evidenced by the fact that it was translocated away from the Bx cluster in Zea mays,moved to other chromosomes in Echinochloa,and even lost in Dichanthelium.Further investigations indicate that purifying selection and polyploidization have shaped the evolutionary trajectory of Bx clusters in the grass family.This study provides the first candidate case of HT of a BGC between plants and sheds new light on the evolution of BGCs.

板蓝根中甙类成分的研究

从板蓝(Baphicacanthuscusia(Nees) Bremek.)根甲醇提取物的正丁醇萃取部分中分离鉴定了4个甙类成分,分别为(2R)-2-O-β-D-吡喃葡萄糖基- 1,4-苯并噁嗪-3-酮(1)、(2R)-2-O-β-D-吡喃葡萄糖基-4-羟基-1,4-苯并噁嗪-3-酮(2)、松脂酚-4-O-β-D-芹菜糖基- (1→2)-β-D-吡喃葡萄糖甙(3) 和尿苷。这些化合物均为首次从板蓝根中发现。板蓝根中存在苯并噁嗪酮衍生物(1和2)可能与其消炎作用有关。

苯并噁嗪类化合物研究进展

以丁布(2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one,DIMBOA)为代表的苯并噁嗪类化合物是广泛存在于禾本科作物中的次生物质,对植物病虫害具有广谱抗性,上世纪中叶开始即引起人们重视并开始了一系列研究。近年来,随着分子生物学技术的应用和诱导抗性理论的发展,对这类物质的功能有了进一步的认识。该文综述这类化学物质的最新研究进展。苯并噁嗪类化合物是从色氨酸合成途径分支出来的一类次生代谢物,其含量是随着植物组织和年龄而变化的;植食性昆虫的取食和病菌的感染能够引起苯并嗪类化合物含量的变化以及苯并噁嗪糖苷的水解。基于其独特的分子结构,苯并噁嗪类化合物具有多种生物活性作用,包括抗虫性、对植物的毒性、抗病性、化感作用等。

苯并噁唑嗪酮类化合物的研究进展

苯并噁唑嗪酮化合物是禾本科作物中一类重要的植物次生代谢物,具有抗菌、抗虫、化感等重要生物活性,此类化合物的研究一直是近几年的热点。本文介绍了其在植物中的分布、结构、种类、生物合成、遗传性和生物活性。

麦类全谷物中生物标记物质的研究进展

全谷物除了含有淀粉、脂质和蛋白等主要营养元素之外,还含有许多对人体有益的健康成分,且大多存在于谷物的皮层或胚芽中。现有研究表明其中一些生物活性成分,如烷基间苯二酚、苯并恶唑嗪酮、燕麦蒽酰胺和皂苷等还具有作为生物标记物的潜力,可用于鉴定全谷物以及精确反映人体中全谷物摄入量,有助于评估全谷物品质和深入了解全谷物对人体健康的影响。本文综述了小麦、大麦、黑麦、燕麦等麦类全谷物中潜在的生物标记物的研究进展,以期为全谷物中生物标记物的研究提供借鉴。

ZmMYC2s play important roles in maize responses to simulated herbivory and jasmonate

Both herbivory and jasmonic acid(JA)activate the biosynthesis of defensive metabolites in maize,but the mechanism underlying this remains unclear.We generated maize mutants in which ZmMYC2a and ZmMYC2b,two transcription factor genes important in JA signaling,were individually or both knocked out.Genetic and biochemical analyses were used to elucidate the functions of ZmMYC2 proteins in the maize response to simulated herbivory and JA.Compared with the wild-type(WT)maize,the double mutant myc2ab was highly susceptible to insects,and the levels of benzoxazinoids and volatile terpenes,and the levels of their biosynthesis gene transcripts,were much lower in the mutants than in the WT maize after simulated insect feeding or JA treatment.Moreover,ZmMYC2a and ZmMYC2b played a redundant role in maize resistance to insects and JA signaling.Transcriptome and Cleavage Under Targets and TagmentationSequencing(CUT&Tag-Seq)analysis indicated that ZmMYC2s physically targeted 60%of the JAresponsive genes,even though only 33%of these genes were transcriptionally ZmMYC2-dependent.Importantly,CUT&Tag-Seq and dual luciferase assays revealed that ZmMYC2s transactivate the benzoxazinoid and volatile terpene biosynthesis genes IGPS1/3,BX10/11/12/14,and TPS10/2/3/4/5/8 by directly binding to their promoters.Furthermore,several transcription factors physically targeted by ZmMYC2s were identified,and these are likely to function in the regulation of benzoxazinoid biosynthesis.This work reveals the transcriptional regulatory landscapes of both JA signaling and ZmMYC2s in maize and provides comprehensive mechanistic insight into how JA signaling modulates defenses in maize responses to herbivory through ZmMYC2s.

9,10-KODA,an α-ketol produced by the tonoplastlocalized 9-lipoxygenase ZmLOX5,plays a signaling role in maize defense against insect herbivory

13-Lipoxygenases(LOXs)initiate the synthesis of jasmonic acid(JA),the best-understood oxylipin hormone in herbivory defense.However,the roles of 9-LOX-derived oxylipins in insect resistance remain unclear.Here,we report a novel anti-herbivory mechanism mediated by a tonoplast-localized 9-LOX,ZmLOX5,and its linolenic acid-derived product,9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid(9,10-KODA).Transposon-insertional disruption of ZmLOX5 resulted in the loss of resistance to insect herbivory.lox5 knockout mutants displayed greatly reduced wound-induced accumulation of multiple oxylipins and defense metabolites,including benzoxazinoids,abscisic acid(ABA),and JA-isoleucine(JA-Ile).However,exogenous JA-Ile failed to rescue insect defense in lox5 mutants,while applications of 1 mM 9,10-KODA or the JA precursor,12-oxo-phytodienoic acid(12-OPDA),restored wild-type resistance levels.Metabolite profiling revealed that exogenous 9,10-KODA primed the plants for increased production of ABA and 12-OPDA,but not JA-Ile.While none of the 9-oxylipins were able to rescue JA-Ile induction,the lox5 mutant accumulated lower wound-induced levels of Ca^(2+),suggesting this as a potential explanation for lower wound-induced JA.Seedlings pretreated with 9,10-KODA exhibited rapid or more robust woundinduced defense gene expression.In addition,an artificial diet supplemented with 9,10-KODA arrested fall armyworm larvae growth.Finally,analysis of single and double lox5 and lox10 mutants showed that ZmLOX5 also contributed to insect defense by modulating ZmLOX10-mediated green leaf volatile signaling.Collectively,our study uncovered a previously unknown anti-herbivore defense and hormonelike signaling activity for a major 9-oxylipin α-ketol.

The Auxin-Regulated Protein ZmAuxRPI Coordinates the Balance between Root Growth and Stalk Rot Disease Resistance in Maize

To optimize fitness, plants must efficiently allocate their resources between growth and defense. Although phytohormone crosstalk has emerged as a major player in balancing growth and defense, the genetic basis by which plants man age this balance remai ns elusive. We previously ide ntified a quantitative disease . resistance locus, qRfg2, in maize (Zea mays) that protects against the fungal disease Gibberella stalk rot. Here, through map-based cloning, we demonstrate that the causal gene at qRfg2 is ZmAuxRPI, which encodes a plastid stroma-localized auxin-regulated protein. ZmAuxRPI responded quickly to pathogen challenge with a rapid yet transient reduction in expression that led to arrested root growth but enhanced resista nee to Gibberella stalk rot and Fusarium ear rot. ZmAuxRPI was show n to promote the biosynthesis of indole-3-acetic acid (IAA), while suppressing the formation of benzoxazinoid defense compounds. ZmAuxRPI presumably acts as a resource regulator modulating indole-3-glycerol phosphate and/or indole flux at the branch point between the IAA and benzoxazinoid biosynthetic pathways. The concerted interplay between IAA and benzoxazinoids can regulate the growth-defense balance in a timely and efficient manner to optimize plant fitness.

先玉335、郑单958和京科968抗虫能力的比较研究

以先玉335、郑单958、京科968为材料,以玉米螟(Ostrinia furnacalis)、黏虫(Mythimna separata)和禾谷缢管蚜(Rhopalosiphum padi)为供试昆虫,探究玉米品系大喇叭口期对玉米螟和黏虫及抽雄期对禾谷缢管蚜抗性差异,测定其主要抗虫化合物丁布类物质的含量。结果发现,京科968对玉米螟及禾谷缢管蚜抗性均高于另外两个品系;对黏虫的抗性,郑单958和京科968高于先玉335。大喇叭口期京科968中丁布类物质含量最高,抽雄期郑单958和京科968中主要丁布成分含量均高于先玉335,上述组织中丁布合成相关基因在郑单958及京科968中的表达量也均高于先玉335。本研究揭示杂交玉米抗虫性与抗性相关化合物含量及其相关基因表达间存在正向相关关系,为抗虫玉米分子育种提供理论参考。

苯并恶唑嗪酮类化合物功能与生物合成研究进展

苯并恶唑嗪酮(benzoxazinoids,BXs)是植物体内一种重要的次生代谢物,因其具有防御作用和化感作用得到了广泛的关注和研究。随着基因组学及分子生物学的发展,苯并恶唑嗪酮的生物合成在分子领域的研究取得了很大的进展。介绍了苯并恶唑嗪酮概况、苯并恶唑嗪酮的功能以及苯并恶唑嗪酮生物合成参与基因及表达调控。

植物中防御相关物质苯并噁嗪类的研究进展

苯并噁嗪类(BXs)化合物是禾本科中广泛存在的一类与防御相关的次生代谢物,主要为苯并噁嗪酮和苯并噁唑啉酮两大类。该类物质以不同的形式存在于植物的不同组织,参与植物的各种防御反应,帮助植物抵抗生物和非生物胁迫。本文综述了BXs的合成与分布、提取和鉴定、诱导影响因子以及多重防御功能。近期的研究表明,BXs除了具有杀虫、抗病、化感等作用外,还能络合金属离子并作为信号因子参与调节其他防御反应,如影响根食动物取食,调控开花时长和生长素代谢,调控根际微生物群落等。对BXs结构和功能的全面了解,有助于将该类物质开发成为新型环境友好型的抗有害生物的化合物,同时挖掘更多与BXs防御功能相关的基因,为农田系统有害生物防治和可持续发展增添新思路和方向。