The dicer-like1 Homolog fuzzy tassel Is Required for the Regulation of Meristem Determinacy in the Inflorescence and Vegetative Growth in Maize

Plant architecture is determined by meristems that initiate leaves during vegetative development and flowers during reproductive development. Maize (Zea mays) inflorescences are patterned by a series of branching events, culminating in floral meristems that produce sexual organs. The maize fuzzy tassel (fzt) mutant has striking inflorescence defects with indeterminate meristems, fasciation, and alterations in sex determination. fzt plants have dramatically reduced plant height and shorter, narrower leaves with leaf polarity and phase change defects. We positionally cloned fzt and discovered that it contains a mutation in a dicer-like1 homolog, a key enzyme required for microRNA (miRNA) biogenesis. miRNAs are small noncoding RNAs that reduce target mRNA levels and are key regulators of plant development and physiology. Small RNA sequencing analysis showed that most miRNAs are moderately reduced in fzt plants and a few miRNAs are dramatically reduced. Some aspects of the fzt phenotype can be explained by reduced levels of known miRNAs, including miRNAs that influence meristem determinacy, phase change, and leaf polarity. miRNAs responsible for other aspects of the fzt phenotype are unknown and likely to be those miRNAs most severely reduced in fzt mutants. The fzt mutation provides a tool to link specific miRNAs and targets to discrete phenotypes and developmental roles.     

The Mechanics of the Grass Flower: Anther Dehiscence and Pollen Shedding in Maize

In this paper on the flower mechanics of the grasses, the openingmechanism of the maize anther is studied. Both the septum betweeneach two locules and the stomium of these porate-dehiscing anthersappear to be opened due to lysis of the middle lamellae of theircells. Additional mechanical force of the expanding pollen mightbe necessary to completely dissociate the parenchyma cells ofthe septum. A number of hours before anthesis the anther isstructurally able to dehisce. At anthesis the dehydrating endotheciumcells bend the locule walls bordering the pore in outward direction.Presumably evaporation is not the only cause for this dehydration. Poaceae; Zea mays ; flower; anther; dehiscence; endothecium; pollen     

MRN1 Implicates Chromatin Remodeling Complexes and Architectural Factors in mRNA Maturation

A functional relationship between chromatin structure and mRNA processing events has been suggested, however, so far only a few involved factors have been characterized. Here we show that rsc nhp6ΔΔ mutants, deficient for the function of the chromatin remodeling factor RSC and the chromatin architectural proteins Nhp6A/Nhp6B, accumulate intron-containing pre-mRNA at the restrictive temperature. In addition, we demonstrate that rsc8-ts16 nhp6ΔΔ cells contain low levels of U6 snRNA and U4/U6 di-snRNA that is further exacerbated after two hours growth at the restrictive temperature. This change in U6 snRNA and U4/U6 di-snRNA levels in rsc8-ts16 nhp6ΔΔ cells is indicative of splicing deficient conditions. We identify MRN1 (multi-copy suppressor of rsc nhp6ΔΔ) as a growth suppressor of rsc nhp6ΔΔ synthetic sickness. Mrn1 is an RNA binding protein that localizes both to the nucleus and cytoplasm. Genetic interactions are observed between 2 µm-MRN1 and the splicing deficient mutants snt309Δ, prp3, prp4, and prp22, and additional genetic analyses link MRN1, SNT309, NHP6A/B, SWI/SNF, and RSC supporting the notion of a role of chromatin structure in mRNA processing.     

The DEFECTIVE IN ANTHER DEHISCENCE1 Gene Encodes a Novel Phospholipase A1 Catalyzing the Initial Step of Jasmonic Acid Biosynthesis, Which Synchronizes Pollen Maturation, Anther Dehiscence, and Flower Opening in Arabidopsis

The Arabidopsis mutant defective in anther dehiscence1 (dad1) shows defects in anther dehiscence, pollen maturation, and flower opening. The defects were rescued by the exogenous application of jasmonic acid (JA) or linolenic acid, which is consistent with the reduced accumulation of JA in the dad1 flower buds. We identified the DAD1 gene by T-DNA tagging, which is characteristic to a putative N-terminal transit peptide and a conserved motif found in lipase active sites. DAD1 protein expressed in Escherichia coli hydrolyzed phospholipids in an sn-1–specific manner, and DAD1–green fluorescent protein fusion protein expressed in leaf epidermal cells localized predominantly in chloroplasts. These results indicate that the DAD1 protein is a chloroplastic phospholipase A1 that catalyzes the initial step of JA biosynthesis. DAD1 promoter::β-glucuronidase analysis revealed that the expression of DAD1 is restricted in the stamen filaments. A model is presented in which JA synthesized in the filaments regulates the water transport in stamens and petals.     

The Interaction of knotted1 and thick tassel dwarf1 in Vegetative and Reproductive Meristems of Maize

In Arabidopsis, SHOOT MERISTEMLESS (STM) and CLAVATA1 (CLV1) competitively regulate meristem homeostasis. Here, we explore the interaction of their maize homologs knotted1 (kn1) and thick tassel dwarf1 (td1). kn1 mutants form fewer lateral organs and td1 inflorescences are fasciated with additional floral organs. Double mutants show kn1 epistatic to td1 in seedling and ear development but dose-sensitivity exists later to promote leaf initiation. Thus kn1 and td1 function in a pathway to maintain meristem homeostasis but their products may interact with different partners during development.     

Analysis of Leaf Sectors in the NCS6 Mitochondrial Mutant of Maize

The nonchromosomal stripe (NCS6) mutation of maize is a partial deletion of the mitochondrial cytochrome oxidase subunit 2 (Cox2) gene. The Cox2 deletion and a narrow yellow striping phenotype are inherited together in a maternal fashion. The striped plants are heteroplasmic for mutant and normal Cox2 genes. Only the mutant Cox2 gene is detected within the yellow stripes, whereas both normal and mutant forms of the gene are present in the green sectors of the NCS6 plants. In the green leaves of nonstriped relatives, only the normal Cox2 gene is found. Both the structure and functioning of the chloroplasts in the yellow leaf sectors of NCS6 plants are altered. The pleiotropic effects of the NCS6 mutation suggest that mitochondrial function is required for the development of photosynthetically competent chloroplasts.     

Characterization of the Arrest in Anther Development Associated with Gibberellin Deficiency of the gib-1 Mutant of Tomato

The role of gibberellins in flower bud development was investigated by studying the gib-1 mutant of tomato, Lycopersicon esculentum. This gibberellin-deficient mutant initiates flower buds, but floral development is not completed unless the mutant is treated with gibberellin. Treatment with other plant growth regulators does not induce normal flower development. Development of gib-1 flower buds, as measured by progress toward anthesis, ceases at a bud length of 2.5 millimeters; however, increase in size of the bud continues. Buds between 2.5 and 3.7 millimeters are developmentally arrested but still are capable of developing normally after treatment with gibberellic acid. Anthers of these developmentally arrested buds contain pollen mother cells that are in the G1 phase of premeiotic interphase. Following treatment of developmentally arrested buds with gibberellic acid, premeiotic DNA synthesis and callose accumulation in pollen mother cells are evident by 48 hours posttreatment, and within 66 hours, prophase I of meiosis- and meiosis-related changes in tapetum development are observable.     

Experimental Analysis of Tassel Development in the Maize Mutant Tassel Seed 6

The maize (Zea mays L.) mutation Tassel seed 6 (Ts6) disrupts both sex determination in the tassel and the pattern of branching in inflorescences. This results in the formation of supernumerary florets in tassels and ears and in the development of pistils in tassel florets where they are normally aborted. A developmental analysis indicated that extra florets in Ts6 inflorescences are most likely the result of delayed determinacy in spikelet meristems, which then initiate additional floret meristems rather than initiating floral organs as in wild type. I have used culturing experiments to assay whether delayed determinacy of Ts6 mutant tassels is reflected in an altered timing of specific determination events. Length of the tassel was used as a developmental marker. These experiments showed that although Ts6 tassels elongate much more slowly than wild type, both mutant and wild-type tassels gained the ability to form flowers with organs of normal morphology in culture at the same time. In situ hybridization patterns of expression of the maize gene Kn, which is normally expressed in shoot meristems and not in determinate lateral organs, confirmed that additional meristems, rather than lateral organs, are initiated by spikelet meristems in Ts6 tassels.     

microRNA在玉米生长发育及非生物胁迫响应中的调控功能

microRNA（miRNA）是一类广泛存在于真核生物中长度为20~24 nt的内源非编码小RNA，它们通过对靶基因mRNA进行切割或翻译抑制，在转录后水平调控靶基因的表达。近期研究表明，miRNA参与植物生长发育与逆境胁迫响应的多个重要生物学过程，对作物的农艺性状也起到重要的调控作用。玉米作为重要的粮食、饲料和工业原料，提高其产量和品质对于保障世界粮食安全至关重要，然而与模式植物拟南芥和水稻相比，玉米中miRNA的研究仍然相对较少，理解miRNA在玉米中的功能和调控机理有助于通过分子育种对关键农艺性状进行遗传改良。本文综述了玉米中miRNA的发现与鉴定，系统总结了参与玉米miRNA代谢途径的关键蛋白DCL、AGO和HEN1的研究进展，重点阐述了在玉米生长发育和非生物胁迫响应过程中已开展功能研究miRNA的调控作用，并对玉米miRNA研究当前存在的问题和未来的发展趋势进行了讨论。     

玉米花药培养和单倍体育种的研究新进展

利用花药培养获得单倍体,从而加速育种进程,是一顶新兴的生物技术,目前在玉米育种中广泛应用,本文综合近几年来国内外玉米的花药培养、单位体育种以及基因工程等方面的研究进展,重点对影响玉米花药培养效率的诸多因素进行了详细论述,并讨论了利用单7保体植株进行基因转导的潜力。     

一个玉米旱敏感突变体的遗传分析与基因定位

玉米干旱胁迫相关突变体在发掘玉米耐旱关键基因研究中具有重要利用价值。在玉米自交系综31的田间扩繁过程中,发现一个玉米干旱胁迫敏感的自然突变体,该突变体在轻度干旱条件下叶片发生卷曲,严重干旱时叶尖变黄,衰老坏死。遗传分析表明突变性状受1对主效单基因控制,表现为隐性遗传,将突变基因命名为DS。利用B73与突变体ds组配F2分离群体,以干旱条件下叶片是否卷曲为指标,将DS基因初定位在第3号染色体SSR标记umc1772和umc2158之间,物理距离为5 Mb。以上研究结果为该基因的克隆及功能分析奠定了基础。     

玉米花药培养和单倍体育种的研究新进展

利用花药培养获得单倍体,从而加速育种进程,是一项新兴的生物技术,目前在玉米育种中广泛应用。本文综合近几年来国内外玉米的花药培养、单倍体育种以及基因工程等方面的研究进展,重点对影响玉米花药培养效率的诸多因素进行了详细论述,并讨论了利用单倍体植株进行基因转导的潜力。     

Fertility,Inheritance and Amino Acid Analysis of Lysine Plus Threonine-Resistant Mutant Progenies of Maize

Sixth generation of mutant maize seed homozygous for lysine plus threonine resistancewhich was derived from the resistant callus cultures has been harvested. The resistance could be inherited stably. The fertility, however, was very poor. The resistant homozygotes have been obtained by backcross of the wild type with the resistant plants (W77-R3019 ×R0), and their fertility could be parlty recovered after selection for the resistant plants from backcross progenies. Genetic analysis showed that the resistance inherited as a single dominant nuclear allele. All of the free amino acids except phenylalan inc in the homozygote are increased by 4 folds. and free essential amino acids by 5 folds which are higher than those in the wild types. Total amino acids increased by 5.53%. The dramatic increase (11 times) in free threonine adds up the total threonine by 17.73%. Difference of the protein content between the homozygote and wild type was not obvious. These results show that selection for the resistance to lysine plus threonine in maize and other cereals is probably very useful for improving their value of protein nutrition.     

水稻台中65与其花粉不育近等基因系的杂种F1的裂药性研究

以台中65及其7个F1花粉不育近等基因系为材料,对水稻亚种间杂种F1裂药性及其与小穗育性的关系进行了研究。结果表明,杂种F1的裂药性受花粉不育基因互作控制。不同杂合座位内等位花粉不育基因互作导致杂种F1花药不开裂的程度不同,S-b座位导致杂种F1部分花药不开裂;不同杂合座位问非等位花粉不育基因互作明显降低杂种F1的裂药程度;杂种F1中含杂合花粉不育基因座位数越多,其裂药指数越小,裂药程度越低,含三个杂合花粉不育基因座位的杂种F1裂药指数为2．27,35．3％的花药不开裂。杂种F1花药不开裂的原因随其所含的杂合花粉不育基因座位种类和数目不同而异。杂种F1裂药程度的下降显著减少落在其柱头上的花粉总数和萌发的花粉数。杂种F1裂药指数和结实率呈极显著的正相关关系。     

A Tandem Duplication Causes the Kn1-O Allele of Knotted, a Dominant Morphological Mutant of Maize

Molecular and genetic techniques are used to define Kn1-O, a mutation which interferes with the normal differentiation of vascular tissue in leaves. Sequences associated with a previously cloned allele, Kn1-2F11, were used as hybridization probes in a Southern analysis of Kn1-O. By this analysis, Kn1-O lacks the Ds2 transposable element that causes Kn1-2F11 but instead is associated with a sequence duplication. Sequence and restriction analysis of genomic clones show that the duplication consists of a tandem array of two 17-kb repeats. Analysis of Kn1-O derivatives indicates that the duplication itself conditions the mutant phenotype; a severely knotted line, Kn1-Ox, has gained a repeat unit to form a triplication, whereas normal derivatives have either lost a repeat unit or sustained insertions that disrupt the tandem duplication. These insertions map near the central junction of the tandem duplication, suggesting that the mutant phenotype results from the novel juxtaposition of sequences. We discuss models that relate the tandem duplication of sequences to altered gene expression.