Tasselseed5 encodes a cytochrome C oxidase that functions in sex determination by affecting jasmonate catabolism in maize

Maize (Zea mays L.) is a monoecious grass plant in which mature male and female florets form the tassel and ear, respectively. Maize is often used as a model plant to study flower development. Several maize tassel seed mutants, such as the recessive mutants tasselseed1 (ts1) and tasselseed2 (ts2), exhibit a reversal in sex determination, which leads to the generation of seeds in tassels. The phenotype of the dominant mutant, Tasselseed5 (Ts5), is similar to that of ts2. Here, we positionally cloned the underlying gene of Ts5 and characterized its function. We show that the GRMZM2G177668 gene is overexpressed in Ts5. This gene encodes a cytochrome C oxidase, which catalyzes the transformation of jasmonoyl‐L‐isoleucine (JA‐Ile) to 12OH‐JA‐Ile during jasmonic acid catabolism. Consistent with this finding, no JA‐Ile peak was detected in Ts5 tassels during the sex determination period, unlike in the wild type. Transgenic maize plants overexpressing GRMZM2G177668 exhibited a tassel‐seed phenotype similar to that of Ts5. These results indicate that the JA‐Ile peak in tassels is critical for sex determination and that the Ts5 mutant phenotype results from the disruption of this peak in tassels during sex determination.     

Class II tassel seed mutations provide evidence for multiple types of inflorescence meristems in maize (Poaceae)

The tassel seed mutations ts4 and Ts6 of maize cause irregular branching in its inflorescences, tassels, and ears, in addition to feminization of the tassel due to the failure to abort pistils. A comparison of the development of mutant and wild-type tassels and ears using scanning electron microscopy reveals that at least four reproductive meristem types can be identified in maize: the inflorescence meristem, the spikelet pair meristem, the spikelet meristem, and the floret meristem. ts4 and Ts6 mutations affect the fate of specific reproductive meristems in both tassels and ears. ts4 mutants fail to form spikelet meristems from spikelet pair meristems. Ts6 mutants are delayed in the conversion of certain spikelet meristems into floret meristems. Once floret meristems are established in both of these mutants, they form florets that appear normal but fail to undergo pistil abortion in the tassel. The abnormal branching associated with each mutant is suppressed at the base of ears, permitting the formation of normal, fertile spikelets. The classification of the different types of reproductive meristems will be useful in interpretation of gene expression patterns in maize. It also provides a framework for understanding meristem functions that can be varied to diversify inflorescence architectures in the Gramineae.     

DEVELOPMENT OF TASSEL SEED 2 INFLORESCENCES IN MAIZE

The normal pattern of maize floral development of staminate florets on the terminal inflorescence (tassel) and pistillate florets on the lateral inflorescences (ears) is disrupted by the recessive mutation tassel seed 2. Tassel seed 2 mutant plants develop pistillate florets instead of staminate florets in the tassel. In addition, the ears of tassel seed 2 plants display irregular rowing of kernels due to the development of the normally suppressed lower floret of each spikelet. The morphology of tassel and ear florets of the recessive maize mutant tassel seed 2 has been compared to those of wild-type maize through development. We have identified the earliest stages at which morphological signs of sex differentiation are evident. We find that sex determination occurs during the same stage on tassel and ear development. Early postsex determination morphology of florets in wild-type ears and in tassel seed 2 tassels and ears is identical.     

Regulation of sex determination in maize

Maize develops separate male and female flowers in different locations on a single plant. Male flowers develop at the tip of the shoot in the tassel, and female flowers develop on the ears, which terminate short branches. The development of male flowers in tassels and female flowers in ears is the result of selective abortion of pistils or stamens, respectively, in developing florets. Genetic analysis has shown that stamen abortion and pistil abortion are under the control of two different genetic pathways. Local levels of the plant hormone gibberellic acid determine whether or not stamens are suppressed. Pistil abortion is under the regulation of the tassel seed genes, one of which has been shown to encode a short-chain alcohol dehydrogenase. The tassel seed genes play a role in regulating the fate of inflorescence meristems as well as pistil primordium fate.     

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.     

BRANCHED SILKLESS mediates the transition from spikelet to floral meristem during Zea mays ear development

The molecular and genetic control of inflorescence and flower development has been studied in great detail in model dicotyledonous plants such as Arabidopsis and Antirrhinum . In contrast, little is known about these important developmental steps in monocotyledonous species. Here we report the analysis of the Zea mays mutant branched silkless1–2 (bd1–2) , allelic to bd1 , which we have used as a tool to study the transition from spikelet to floret development in maize. Floret development is blocked in the female inflorescence (the ear) of bd1–2 plants, whereas florets develop almost normally in the male inflorescence (the tassel). Detailed phenotypic analyses indicate that in bd1–2 mutants ear inflorescence formation initiates normally, however, the spikelet meristems do not proceed to form floret meristems. The ear spikelets, at anthesis, contain various numbers of spikelet-like meristems and glume-like structures. Furthermore, growth of branches from the base of the ear is often observed. Expression analyses show that the floral-specific MADS box genes Zea mays AGAMOUS1 ( ZAG1 ), ZAG2 and Zea mays MADS 2 ( ZMM2 ) are not expressed in ear florets in bd1–2 mutants, whereas their expression in tassel florets is similar to that of wild type. Taken together, these data indicate that the development from spikelet to floret meristem is differentially controlled in the ear and tassel in the monoecious grass species Zea mays , and that BRANCHED SILKLESS plays an important role in regulating the transition from spikelet meristem to floral meristem during the development of the female inflorescence of maize.     

New insight in the Gibberellin biosynthesis and signal transduction

Gibberellin (GA) plays important roles through plant growth and development. However, where GA is synthesized inside a cell and how it regulates sex determination is obscure. We analyzed the classic dwarf1 (d1) mutant in maize and revealed that D1 encodes GA 3-oxidase converting inactive GA intermediates to bioactive GA. As such, the D1 protein marks the sites where GA is potentially synthesized. Interestingly, the D1 protein was found to localize in the cytosol and nucleus, a dual-localization coinciding with the GA receptor. The same result was found for GA 20-oxidase catalyzing the upstream reaction. These results suggest that GA can be synthesized in the cytosol and nucleus. The D1 protein was highly and specifically expressed in the stamen primordia in the ear florets, but low in the whole tassel. Hence it is possible that low level of GA in the tassel is insufficient to suppress stamen development. As jasmonic acid (JA) plays antagonistic role to GA in the tassel florets, here we propose a model to explain this antagonism effect on the regulation of the stamen and pistil organ development in the tassel florets in maize.     

SUSTAINED TREATMENT WITH GIBBERELLIC ACID OF MAIZE PLANTS CARRYING ONE OF THE DOMINANT GENES TEOPOD AND CORN-GRASS

Nickerson , Norton H. (Washington U., St. Louis, Missouri.) Sustained treatment with gibberellic acid of maize plants carrying one of the dominant genes Teopod and Corn-grass. Amer. Jour. Bot. 47(10): 809–815. Illus. 1960.—Groups of field-grown plants of 2 dominant maize mutants, Corn-grass (Cg), and Teopod (Tp), were treated with either distilled water or with 1 of 3 concentrations of aqueous gibberellic acid (GA) every 3 days from the seedling stage until tassel emergence. Both dominant mutants were found to respond to GA in such manner that certain treated plants became essentially normal in phenotype. The role of GA in modifying expression of specific genes is briefly discussed.     

More mog genes that influence the switch from spermatogenesis to oogenesis in the hermaphrodite germ line of Caenorhabditis elegans

The Caenorhobditis elegans XX animal possesses a hermaphrodite germ line, producing first sperm, then oocytes. In this paper, we report the genetic identification of five genes, mog-2, mog-3, mog-4, mog-5, and mog-6, that influence the hermaphrodite switch from sper-matogenesis to oogenesis. In mcg-2-mog-6 mutants, spermatogenesis continues past the time at which hermaphrodites normally switch into oogenesis and no oocytes are observed. Therefore, in these mutants, germ cells are transformed from a female fate (oocyte) to a male fate (sperm). The fem-3 gene is one of five genes that acts at the end of the germline sex determination pathway to direct spermatogenesis. Analyses of mog;fem-3 double mutants suggest that the mog-2-mog-6 genes act before fem-3; thus these genes may be in a position to negatively regulate fem-3 or one of the other terminal regulators of germline sex determination. Double mutants of fem-3 and any one of the mog mutations make oocytes. Using these double mutants, we show that oocytes from any mog;fem-3 double mutant are defective in their ability to support embryogenesis. This maternal effect lethality indicates that each of the mog genes is required for embryogenesis. The two defects in mog-2-mog-6 mutants are similar to those of mog-1: all six mog genes eliminate the sperm/oocyte switch in hermaphrodites and cause maternal effect lethality. We propose that the mog-2-mog-6 mutations identify genes that act with mog-1 to effect the sperm/oocyte switch. We further speculate that the mog-1-mog-6 mutations all interfere with translational controls of fem-3 and other maternal mRNAs. © 1993 Wiley-Liss, Inc.     

两个相关基因表达量和SNP与玉米雄穗大小相关

玉米雄穗通常较发达,散粉量大于授粉需要,过量消耗能量会影响光合产物向果穗的分配,过于发达的雄穗还会影响群体透光性、降低光合效率。生产实践和育种研究证明,由于雄穗大小与玉米籽粒产量负相关,因此成为品种选育的间接选择指标。该研究根据前人的报道,从11个雄穗大小不同的玉米自交系中扩增角蛋白相关蛋白基因KAP5-4和受体样蛋白激酶基因CLV1的基因组序列,多重比较后用以分析其开放阅读框、保守结构和单核苷酸多态性,用荧光实时定量PCR检测其在雄穗原基中的差异表达,并与雄穗分枝数和雄穗干重两个度量雄穗小的指标进行了相关分析。结果表明:KAP5-4基因的相对表达量与雄穗分枝数(r=0.77,P0.01)和雄穗干重正相关(r=0.83,P0.01)。11个自交系的CLV1基因开放框在2 104 bp存在单核苷酸多态性,其中5个自交系的2 014~2 016 bp核苷酸组成密码子GAC,编码受体样蛋白第702位酸性的天冬氨酸,另6个自交系的2 014~2 016 bp核苷酸组成密码子AAC,编码受体样蛋白第702位极性天冬氨酰胺。在前5个自交系中,CLV1基因的相对表达量与雄穗分枝数(r=-0.92,P0.01)和雄穗干重(r=-0.91,P0.05)负相关;而在后6个自交系中,仅与雄穗干重负相关(r=-0.91,P0.05)。综上所述,KAP5-4和CLV1基因的表达和单核苷酸多态性与玉米雄穗大小关系密切,可开发功能性的DNA标记用于玉米育种的分子标记辅助选择。     

Use of homeotic mutation tasselseed2 for investigation of the action of maize meiotic genes during micro-and megasporogenesis

The manifestation of the ms43 maize meiotic mutation in the megasporogenesis of ts2 ms43 double mutants has been studied. Combined genetical and cytological analysis of the progeny of diheterozygote selfing showed that the ms43 mei gene was not microsporogenesis-specific. The manifestation of ms43 in megasporogenesis of the double mutants proved to be affected by the ts2 mutation. It prevented formation of the phenotype characteristic of ms43 and distorted early developmental stages of the entire ovule. It is the first study of megasporogenesis in tasselseed2 transformed tassels. Cytological data on the afd1 mutation in single and double mutants are presented. Possible mechanisms of the interaction between the ms43 and ts2 mutations are discussed.     

The FUSCA genes of Arabidopsis: negative regulators of light responses

More than 200 fusca mutants of Arabidopsis have been isolated and characterised, defining 14 complementation groups. Mutations in at least nine FUSCA genes cause light-dependent phenotypic changes in the absence of light: high levels of anthocyanin accumulation in both the embryo and the seedling, inhibition of hypocotyl elongation, apical hook opening, and unfolding of cotyledons. In double mutants, the fusca phenotype is epistatic to the hy phytochromedeficiency phenotype, indicating that the FUSCA genes act downstream of phytochrome. By contrast, the accumulation of anthocyanin is suppressed by mutations in TT and TTG genes, which affect the biosynthesis of anthocyanin, placing the FUSCA genes upstream of those genes. Regardless of the presence or absence of anthocyanin, fusca mutations limit cell expansion and cause seedling lethality. In somatic sectors, mutant fus1 cells are viable; expressing tissue-specific phenotypes: reduced cell expansion and accumulation of anthocyanin in subepidermal tissue, formation of ectopic trichomes but no reduced cell expansion in epidermal tissue. Our results suggest a model of FUSCA gene action in light-induced signal transduction.     

Joint‐linkage mapping and GWAS reveal extensive genetic loci that regulate male inflorescence size in maize

Both insufficient and excessive male inflorescence size leads to a reduction in maize yield. Knowledge of the genetic architecture of male inflorescence is essential to achieve the optimum inflorescence size for maize breeding. In this study, we used approximately eight thousand inbreds, including both linkage populations and association populations, to dissect the genetic architecture of male inflorescence. The linkage populations include 25 families developed in the U.S. and 11 families developed in China. Each family contains approximately 200 recombinant inbred lines (RILs). The association populations include approximately 1000 diverse lines from the U.S. and China. All inbreds were genotyped by either sequencing or microarray. Inflorescence size was measured as the tassel primary branch number (TBN) and tassel length (TL). A total of 125 quantitative trait loci (QTLs) were identified (63 for TBN, 62 for TL) through linkage analyses. In addition, 965 quantitative trait nucleotides (QTNs) were identified through genomewide study (GWAS) at a bootstrap posterior probability (BPP) above a 5% threshold. These QTLs/QTNs include 24 known genes that were cloned using mutants, for example Ramosa3 (ra3), Thick tassel dwarf1 (td1), tasselseed2 (ts2), liguleless2 (lg2), ramosa1 (ra1), barren stalk1 (ba1), branch silkless1 (bd1) and tasselseed6 (ts6). The newly identified genes encode a zinc transporter (e.g. GRMZM5G838098 and GRMZM2G047762), the adapt in terminal region protein (e.g. GRMZM5G885628), O‐methyl‐transferase (e.g. GRMZM2G147491), helix‐loop‐helix (HLH) DNA‐binding proteins (e.g. GRMZM2G414252 and GRMZM2G042895) and an SBP‐box protein (e.g. GRMZM2G058588). These results provide extensive genetic information to dissect the genetic architecture of inflorescence size for the improvement of maize yield.     

Some maize sex-related mutants

Four morphological sex-related mutants in maize (Zea mays L.) are described. Three have arisen in materials containing transposons and one (Mn::Uq) is known to be segregating with a transposon. The Mn::Uq and the RSS affect pollen activity, fw affects tassel silking, and ba4 lacks ear initials. These mutants have been studied by genetic means, and some interactions between double mutants have been investigated. Received: 15 December 2000 / Accepted: 30 April 2001     

Action of the Tunicate locus on maize floral development

The co-dominant Tunicate (Tu) mutation in maize causes nonreproductive structures in both the male and female inflorescences to be enlarged. This mutation also affects sex determination, permitting the development of pistils in the normally staminate tassel. In order to characterize the role of the normal tu gene product, we have analysed genetic interaction between Tu and other mutations that perturb specific stages of floral development. Synergistic interactions observed suggested that the tu product functions in at least three stages of floral development–determination of spikelet primordia, differentiation of non-reproductive organs and pistil abortion in the tassel. © 1994 Wiley-Liss, Inc.     

Mutations in somePolycomb group genes ofDrosophila interfere with regulation of segmentation genes

Mutations in severalPolycomb (Pc) group genes cause maternal-effect or zygotic segmentation defects, suggesting thatPc group genes may regulate the segmentation genes ofDrosophila. We show that individuals doubly heterozygous for mutations inpolyhomeotic and six otherPc group genes show gap, pair rule, and segment polarity segmentation defects. We examined double heterozygous combinations ofPc group and segmentation mutations for enhancement of adult and embryonic segmentation defects.Posterior sex combs andpolyhomeotic interact withKrüppel ² and enhance embryonic phenotypes ofhunchback andknirps, andpolyhomeotic enhanceseven-skipped. Surprisingly, flies carrying duplications ofextra sex combs (esc), that were heterozygous for mutations ofeven-skipped (eve), were extremely subvital. Embryos and surviving adults of this genotype showed strong segmentation defects in even-numbered segments. Antibody studies confirm that expression ofeve is suppressed by duplications ofesc. However,esc duplications have no effect on other gap or pair rule genes tested. To our knowledge, this is only the second triplo-abnormal phenotype associated withPc group genes. Duplications of nine otherPc group genes have no detectable effect oneve. Expression ofengrailed (en) was abnormal in the central nervous systems of mostPc group mutants. These results support a role forPc genes in regulation of some segmentation genes, and suggest thatesc may act differently from otherPc group genes.     

Temperature-sensitive mutations in various genes of Escherichia coli K12 can be suppressed by the ssrA gene for 10Sa RNA (tmRNA)

An Escherichia coli strain with a deletion in the ssrA gene that encodes 10Sa RNA (tmRNA) was used to screen for temperature-sensitive (ts) mutants whose ts phenotypes were suppressible by introduction of the wild-type ssrA gene. Mutants in four different genes were isolated. Ts mutants of this type were also obtained in a screen for mutations in thyA, the structural gene for thymidylate synthase. The ThyA activity in crude extracts prepared from the ts mutants was temperature-sensitive. The presence of the ssrA gene caused an increase in the total amount of the temperature-sensitive enzyme expressed, rather than suppressing the ts activity of the enzyme itself. SsrA-DD, a mutant form of 10Sa RNA, suppressed the ts phenotype of a thyA mutant, suggesting that degradation of a tagged peptide was not required for suppression of the ts phenotype. Considering the fact that ssrA-suppressible mutants could be isolated as temperature-sensitive mutants with mutations in different genes, it seems evident that trans-translation can occur on mRNA that is not lacking its stop codon.     

The use of extragenic suppressors to define genes involved in protein export in Escherichia coli

Summary The secA gene codes for a membrane component involved in protein export in E. coli. In order to define other genes whose products play such a role, we have characterized extragenic suppressors of a secA(Ts) mutation. These suppressors fall into at least three genetic loci. One such locus is the prlA gene, previously identified by mutations which suppress signal sequence mutants. Thus, this approach may allow the identification of new genes involved in the export process.