Phytohormones in Seedlings of Maize Hybrids Differing in Their Tolerance to High Temperatures

The contents of phytohormones (IAA, ABA, cytokinins, and gibberellin-like compounds) were measured in shoots and roots of eight-day-old seedlings of two maize (Zea mays L.) hybrids differing in their tolerance to elevated temperatures. More tolerant seedlings initially contained more ABA and cytokinins, and the contents of these hormones changed less after a temperature increase than in seedlings of the sensitive hybrid. Hyperthermia induced a destruction of chloroplast lamellar structure in the leaf sheath cells of the sensitive but not of the tolerant hybrid.     

Identification and Fine Mapping of rhm1 Locus for Resistance to Southern Corn Leaf Blight in Maize

rhm1 is a major recessive disease resistance locus for Southern corn leaf blight (SCLB).To further narrow down its genetic position,F 2 population and BC 1 F 1 population derived from the cross between resistant (H95 rhm) and susceptible parents (H95) of maize (Zea mays) were constructed.Using newly developed markers,rhm1 was initially delimited within an interval of 2.5 Mb,and then finally mapped to a 8.56 kb interval between InDel marker IDP961-503 and simple sequence repeat (SSR) marker A194149-1.Three polymorphic markers IDP961-504,IDP B2-3 and A194149-2 were shown to be co-segregated with the rhm1 locus.Sequence analysis of the 8.56 kb DNA fragment revealed that it contained only one putative gene with a predicted amino acid sequence identical to lysine histidine transporter 1 (LHT1).Comparative sequence analysis indicated that the LHT1 in H95 rhm harbors a 354 bp insertion in its third exon as compared with that of susceptible alleles in B73,H95 and Mo17.The 354 bp insertion resulted in a truncation of the predicted protein of candidate resistance allele (LHT1-H95 rhm).Our results strongly suggest LHT1 as the candidate gene for rhm1 against SCLB.The tightly linked molecular markers developed in this study can be directly used for molecular breeding of resistance to Southern corn leaf blight in maize.     

外引玉米种质对两种穗腐病原镰孢菌抗性鉴定

采用双牙签接种技术,2016-2017年连续2年对从美国、加拿大、罗马尼亚、德国、法国、荷兰等国家引进的177份玉米种质资源抗玉米穗腐病原拟轮枝镰孢(F.verticillioides)和禾谷镰孢(F.graminearum)进行了鉴定。结果表明,鉴定的177份玉米种质资源中,对拟轮枝镰孢表现高抗(HR)的资源2份,占总数的1.13%;抗病(R)38份,占总数的21.47%;中抗(MR)75份,占总数的42.37%;感病(S)48份,占总数的27.12%;高感(HS)14份,占总数的7.91%。177份玉米种质资源中,对禾谷镰孢(F.graminearum)表现抗病(R)12份,占鉴定资源总数的6.78%;中抗(MR)66份,占总数的37.29%;感病(S)64份,占总数的36.16%;高感(HS)35份,占总数的19.77%,未发现对禾谷镰孢菌表现高抗的材料。在177份玉米种质资源中,兼抗两种穗腐病原镰孢菌的种质资源有12份。     

General and Exact Inbreeding Coefficient of Maize Synthetics Derived from Three-Way Line Hybrids

Synthetic varieties (SVs) are populations generated by randomly mating their parents. They are a good alternative for low-input farmers who grow onions, maize, and other allogamous crops since the seed produced by a SV does not change from one generation to the next. Although SV progenitors are commonly pure lines, in this case a synthetic (Syn_TC) whose parents are t three-way line crosses, a very common type of maize hybrid grown in Mexico, is studied. The aim was to develop a general and exact equation for the inbreeding coefficient of a Syn_TC Syn_TC because of its relationship with the mean of economically important traits. This objective arose due to the need for a more advanced study in terms of determining whether Syn_TC can be applied specifically and accurately for any number of parents (t), plants per parent (m) and inbreeding coefficient (IC) of the initial lines (F_L). A formula for the IC of the Syn_TC was derived that, given any values of F_L (0 ≤ F_L ≤ 1) and t, is specific for any value of m, not just for “large” numbers associated with the context in which the Hardy-Weinberg law is stated. It was found that Syn_TC is very sensitive to changes in m when m is not greater than eight, after which it tends to stabilize very quickly. In summary, unlike previously derived formulas, Syn_TC is exact for any values of t, m and F_L.     

玉米比较基因组学研究进展

玉米是世界上重要的粮食作物 ,长期以来一直是遗传学、分子生物学和基因组学研究的重点对象。近十多年来 ,涉及到玉米的基因组学研究取得了很大进展。不仅在利用比较遗传作图方法方面发现玉米和其它植物 (尤其是禾谷类作物 )的基因组存在广泛的共线性 ,在较小的DNA区域上也发现存在微共线性。尽管还存在一些共线性的例外情形 ,进一步的比较基因组学研究将深入阐明玉米基因组的结构和进化 ,并把这些研究成果应用于基因发掘中。     

Involvement of FST1 from Fusarium verticillioides in virulence and transport of inositol

Fumonisin B1 (FB1), a polyketide mycotoxin produced by Fusarium verticillioides during the colonization of maize kernels, is detrimental to human and animal health. FST1 encodes a putative protein with 12 transmembrane domains; however, its function remains unknown. The FST1 gene is highly expressed by the fungus in the endosperm of maize kernels compared with the levels of expression in germ tissues. Previous research has shown that FST1 affects FB1 production, virulence, hydrogen peroxide resistance, hydrophobicity and macroconidia production. Here, we examine the phylogeny of FST1, its expression in a Saccharomyces cerevisiae strain lacking a functional myo‐inositol transporter (ITR1) and the effect of amino acid changes in the central loop and C‐terminus regions of FST1 on functionality. The results indicate that expression of FST1 in an ITR1 mutant strain restores growth on myo‐inositol medium to wild‐type levels and restores the inhibitory effects of FB1, suggesting that FST1 can transport both myo‐inositol and FB1 into yeast cells. Our results with engineered FST1 also indicate that amino acids in the central loop and C‐terminus regions are important for FST1 functionality in both S. cerevisiae and F. verticillioides. Overall, this research has established the first characterized inositol transporter in filamentous fungi and has advanced our knowledge about the global regulatory functions of FST1.     

Transcriptional and Metabolic Changes Associated to the Infection by Fusarium verticillioides in Maize Inbreds with Contrasting Ear Rot Resistance

Fusarium verticillioides causes ear rot and grain mycotoxins in maize (Zea mays L.), which are harmful to human and animal health. Breeding and growing less susceptible plant genotypes is one alternative to reduce these detrimental effects. A better understanding of the resistance mechanisms would facilitate the implementation of strategic molecular agriculture to breeding of resistant germplasm. Our aim was to identify genes and metabolites that may be related to the Fusarium reaction in a resistant (L4637) and a susceptible (L4674) inbred. Gene expression data were obtained from microarray hybridizations in inoculated and non-inoculated kernels from both inbreds. Fungal inoculation did not produce considerable changes in gene expression and metabolites in L4637. Defense-related genes changed in L4674 kernels, responding specifically to the pathogen infection. These results indicate that L4637 resistance may be mainly due to constitutive defense mechanisms preventing fungal infection. These mechanisms seem to be poorly expressed in L4674; and despite the inoculation activate a defense response; this is not enough to prevent the disease progress in this susceptible line. Through this study, a global view of differential genes expressed and metabolites accumulated during resistance and susceptibility to F. verticillioides inoculation has been obtained, giving additional information about the mechanisms and pathways conferring resistance to this important disease in maize.     

玉米杂种与亲本穗分化期功能叶基因差异表达与杂种优势

为探讨玉米杂种优势的分子机理,以10个玉米自交系及其组配的38个杂交种为材料,利用cDNA-AFLP技术,分析杂种与亲本在玉米雌穗小穗分化期功能叶片的基因差异表达类型与主要农艺性状的杂种表现及杂种优势的关系。研究表明：（1）杂种的基因相对于其双亲,存在质和量的表达差异,其中质的差异表达类型包括：单亲沉默表达,双亲沉默表达,亲本显性表达和杂种特异表达等类型。（2）在雌穗小穗分化期,同一差异表达类型中不同杂交组合间差异很大;从总体平均看,杂种特异表达类型占25.22%,亲本显性表达类型占21.46%,双亲沉默表达类型占8.27%,单亲沉默表达类型占33.49%。（3）单亲沉默表达与株高的杂种表现呈显著正相关;双亲沉默表达与穗粗的杂种优势呈显著负相关,显性表达与行粒数和单株粒重的杂种优势呈显著负相关,其余表达类型与所有农艺性状杂种表现及杂种优势均不相关,并对结果进行了讨论。     

Investigation and a New Evaluation Method of the Resistance of Maize Hybrids grown in Hungary to Fusarium moulds

Thirty maize hybrids grown in Hungary representing groups FAO 200–299, FAO 400–499 and FAO 500-were studied in order to obtain information about genotypic resistance to Fusarium moulds. The plants were grown on an experimental farm and were inoculated using the toothpick method with Fusarium graminearum and Fusarium culmorum . In addition maize grain meals were also inoculated with isolates of moulds. Measurements were made of the mould-covered surface area of the ears 9 weeks after inoculation and of the zearalenone and T2-toxin content of the inoculated maize meals. Large differences among hybrids were observed for the mould-covered area of the ear surface (2.00–38.88%), the zearalenone content (4.20–71.20 mg/kg) and the T2-toxin content (1.60–122.50 mg/kg). Relatively poor correlation ( r =0.489) was found between the area of mould covering the ear surface and mycotoxin content of maize. Bearing in mind that the user of feed grain is interested in obtaining a feed with the lowest mycotoxin content, a new method of evaluation of hybrids which uses a toxin–mould index (TMI) was introduced. This index is calculated on the basis of both growth rate of moulds and their toxin-producing activity. Although a decreasing tendency in resistance of hybrids with a longer growing vegetation period could be observed, resistant genotypes were found in every FAO group, confirming the views that in addition to the influence of duration of the vegetation period on the resistance, genetic factors may also play a significant role.     

玉米雌、雄穗与叶片内几种激素含量的比较

以甜玉米为材料,采用扫描电镜观察雌、雄花序发育过程,并用ＥＬＩＳＡ 和ＨＰＬＣ 检测雌、雄花序发育过程中内源激素（ｉＰＡｓ 、ＺＲｓ、ＤＨＺＲｓ、ＺＴ、ＩＡＡ、ＧＡ３） 和内源玉米赤霉烯酮（ｚｅａｒａｌｅｎｏｎｅ, ＺＥＮ） 含量,分析激素含量变化与玉米性别决定的关系。结果表明：玉米花序经过了无性、双性到单性的发育过程,在茎尖伸长和小穗原基突起时期,雄花序中内源ｉＰＡｓ、ＺＲｓ、ＧＡ３ 和ＺＥＮ 含量最高并高于雌花序;在玉米性别决定的关键时期,即花器官原基突起到雌、雄性器官选择退化阶段,雄花序中ｉＰＡｓ、ＺＲｓ、ＺＴ 和ＺＥＮ 含量明显增加并高于雌花序,此时在两种花序中的ＧＡ３ 含量差异不明显。正常果穗上、中、下不同部位果穗内源ｉＰＡｓ、ＺＲｓ、ＺＴ、ＧＡ３ 和ＺＥＮ 含量无明显差异,顶端小穗雄性化的果穗顶部内源ｉＰＡｓ、ＺＲｓ、ＺＴ、ＧＡ３ 和ＺＥＮ 含量急剧增加。这些结果说明高水平的细胞分裂素、ＧＡ３ 和ＺＥＮ 可能有利于玉米雄性器官的发育。     

农杆菌介导的玉米原位转化方法改良

原位转化是一种简便的植物转基因方法,在拟南芥中已经应用较为成熟,在玉米上的应用并不多见.本文在玉米开花期间,将含有目标载体pCAMBIA1301的农杆菌菌株LBA4404的细胞悬浮液直接涂抹到事先授粉约8小时后并去除掉苞叶和花丝的幼穗上.转化后种子的幼苗,经过gus活性染色和潮霉素基因(hpt)的PCR扩增,证实有部分的种子T-DNA整合进入了基因组.在潮霉素筛选后,有2.6 %抗性苗存活.其中57.7 %抗性植株表现出GUS阳性,相当于全部检测幼苗的1.5 %.这一结果通过潮霉素基因的PCR扩增,得到进一步的证实.     

Leaf Stripe and Stem Rot Caused by Burkholderia gladioli,a New Maize Disease in Mexico

A disease in maize plants, not previously observed, appeared in 2003–2004 in Cosoleacaque, Tlalixcoyan and Paso de Ovejas counties, in the state of Veracruz, Mexico. Initial symptoms on leaves were small white‐yellow watery spots, which coalesced into dry necrotic stripes 0.3 wide and up to 8 cm long. Reddening sometimes developed on these leaves. Stems developed a rot in the crown. The flag leaf became rot and necrotic at the base, rolled inwards and dried out. Necrosis developed at the base of the corn ears and their growth was inhibited. These symptoms were initially observed in Asgrow‐7573 commercial maize plantings. A bacterium characterized by white colonies, gram negative, aerobic, rod‐shape, opaque, round colonies with entire margins on casaaminoacid peptone and glucose media was consistently isolated from diseased maize plants. On King’s Medium B, the isolates produced yellow, non‐mucoid colonies, with the majority of the strains secreting a diffusible yellow pigment into the media. The bacterium identity was confirmed by PCR amplification and sequencing of 16S and 23S genes rDNA fragments. The bacterium was identified as Burkholderia gladioli. Its pathogenicity on maize plants in Mexico is a new record.     

玉米籽粒胚乳细胞增殖及其与淀粉充实的关系

用纤维素酶解离胚乳、滤膜法统计玉米胚乳细胞的数目,进一步借助Logistic方程模拟胚乳细胞增殖动态的结果表明,整个灌浆期间胚乳细胞增殖呈现“慢-快-慢”的变化趋势。授粉15d后,不同类型胚乳的细胞数目依序为普通玉米〉糯玉米〉甜玉米〉爆裂玉米;胚乳细胞数目主要取决于细胞的增殖速率,并与淀粉充实和粒重关系密切。胚乳发育前期以胚乳细胞增殖为主,后期以淀粉积累为主。     

玉米叶形相关性状的Meta-QTL及候选基因分析

叶长、叶宽、叶面积及叶夹角不仅影响玉米(Zea mays)光合效率, 也是株型的重要构成因素。通过对620个叶形QTL进行整合, 构建不同遗传背景下的叶形QTL整合图谱, 利用元分析发掘出22个叶长、22个叶宽、12个叶面积以及17个叶夹角mQTL; 进一步运用生物信息学手段, 确定44个与叶片发育密切相关的候选基因。分析发现, 仅有NAL7-like、YABBY6- like和GRF2等13个基因位于mQTL区间内, 而玉米中已克隆的KNOTTED1、AN3/GIF1、rgd1/lbl1、mwp1及SRL2-like、HYL1-like和CYCB2;4-like等水稻(Oryza sativa)和拟南芥(Arabidopsis thaliana)叶形同源基因位于未被整合的QTL内; 对44个候选基因在叶片长、宽、厚发育过程中基部-末端、中央-边缘、远轴-近轴的调控机理进行归纳分析, 发现玉米中仅有少数几个候选基因被报道, 揭示了叶形发育的部分分子机理。因此, 对玉米叶形相关mQTL/QTL及基因进行全面深入的分析, 不仅有助于增加对其遗传结构的了解, 发掘更多候选基因, 阐明叶形发育和形成的分子机制, 还可为耐密理想株型的分子标记辅助选择提供依据。     

Defining Plant Resistance to Phytophthora cinnamomi: A Standardized Approach to Assessment

Phytophthora cinnamomi is a soil‐borne plant pathogen that causes devastating disease in agricultural and natural systems worldwide. While a small number of species survive infection by the pathogen without producing disease symptoms, the nature of resistance, especially under controlled conditions, remains poorly understood. At present, there are no standardized criteria by which resistance or susceptibility to P. cinnamomi can be assessed, and we have used five parameters consisting of plant fresh weight, root growth, lesion length, relative chlorophyll content of leaves and pathogen colonization of roots to analyse responses to the pathogen. The parameters were tested using two plant species, Zea mays and Lupinus angustifolius, through a time course study of the interactions and resistance and susceptibility defined 7 days after inoculation. A scoring system was devised to enable differentiation of these responses. In the resistant interaction with Z. mays, there was no significant difference in fresh weight, root length and relative chlorophyll content in inoculated compared with control plants. Both lesion size and pathogen colonization of root tissues were limited to the site of inoculation. Following inoculation L. angustifolius showed a significant reduction in plant fresh weight and relative leaf chlorophyll content, cessation of root growth and increased lesion lengths and pathogen colonization. We propose that this technique provides a standardized method for plant–P. cinnamomi interactions that could be widely used to differentiate resistant from susceptible species.