Inflorescence Formation Research Articles

TAWAWA1 , a regulator of rice inflorescence architecture, functions through the suppression of meristem phase transition

Inflorescence structures result from the activities of meristems, which coordinate both the renewal of stem cells in the center and organ formation at the periphery. The fate of a meristem is specified at its initiation and changes as the plant develops. During rice inflorescence development, newly formed meristems acquire a branch meristem (BM) identity, and can generate further meristems or terminate as spikelets. Thus, the form of rice inflorescence is determined by a reiterative pattern of decisions made at the meristems. In the dominant gain-of-function mutant tawawa1-D, the activity of the inflorescence meristem (IM) is extended and spikelet specification is delayed, resulting in prolonged branch formation and increased numbers of spikelets. In contrast, reductions in TAWAWA1 (TAW1) activity cause precocious IM abortion and spikelet formation, resulting in the generation of small inflorescences. TAW1 encodes a nuclear protein of unknown function and shows high levels of expression in the shoot apical meristem, the IM, and the BMs. TAW1 expression disappears from incipient spikelet meristems (SMs). We also demonstrate that members of the SHORT VEGETATIVE PHASE subfamily of MADS-box genes function downstream of TAW1. We thus propose that TAW1 is a unique regulator of meristem activity in rice and regulates inflorescence development through the promotion of IM activity and suppression of the phase change to SM identity.

The interplay between inflorescence development and function as the crucible of architectural diversity

Most angiosperms present flowers in inflorescences, which play roles in reproduction, primarily related to pollination, beyond those served by individual flowers alone. An inflorescence's overall reproductive contribution depends primarily on the three-dimensional arrangement of the floral canopy and its dynamics during its flowering period. These features depend in turn on characteristics of the underlying branching structure (scaffold) that supports and supplies water and nutrients to the floral canopy. This scaffold is produced by developmental algorithms that are genetically specified and hormonally mediated. Thus, the extensive inflorescence diversity evident among angiosperms evolves through changes in the developmental programmes that specify scaffold characteristics, which in turn modify canopy features that promote reproductive performance in a particular pollination and mating environment. Nevertheless, developmental and ecological aspects of inflorescences have typically been studied independently, limiting comprehensive understanding of the relations between inflorescence form, reproductive function, and evolution. This review fosters an integrated perspective on inflorescences by summarizing aspects of their development and pollination function that enable and guide inflorescence evolution and diversification. The architecture of flowering inflorescences comprises three related components: topology (branching patterns, flower number), geometry (phyllotaxis, internode and pedicel lengths, three-dimensional flower arrangement) and phenology (flower opening rate and longevity, dichogamy). Genetic and developmental evidence reveals that these components are largely subject to quantitative control. Consequently, inflorescence evolution proceeds along a multidimensional continuum. Nevertheless, some combinations of topology, geometry and phenology are represented more commonly than others, because they serve reproductive function particularly effectively. For wind-pollinated species, these combinations often represent compromise solutions to the conflicting physical influences on pollen removal, transport and deposition. For animal-pollinated species, dominant selective influences include the conflicting benefits of large displays for attracting pollinators and of small displays for limiting among-flower self-pollination. The variety of architectural components that comprise inflorescences enable diverse resolutions of these conflicts.

Regulated deficit irrigation in different phenological stages of potted geranium plants: water consumption, water relations and ornamental quality

The irrigation water requirements and sensitivity to water deficits of ornamental plants is of great interest to horticultural producers for planning irrigation strategies. The effect of different deficit irrigation strategies on physiological and morphological parameters in geranium plants was studied in different growth phases to evaluate how such strategies can be safely used and to ascertain whether the flowering phase is sensitive to deficit irrigation. Pelargonium × hortorum L.H. Bailey plants, grown in a controlled growth chamber, were subjected to four irrigation treatments: control (100 % water field capacity throughout the experiment), sustainable deficit irrigation (75 % water field capacity throughout the experiment), and two regulated deficit irrigation treatments that included water stress during the vegetative growth phase or during the flowering development phase. Although the total amount of irrigation water was similar in the three deficit irrigation treatments (around 80 % of the control value), the lowest values for both height and flowering were found when deficit irrigation was applied during flowering. This indicates that plant quality does not only depend on the amount of water applied but also on the time when the reduction is applied, and that flowering is the most sensitive phase to water stress. Evapotranspiration was related to the formation of inflorescences and to increased plant height. When the irrigation strategy was changed, plants increased or decreased their water consumption and stomatal conductance to adjust to the new conditions by regulating stomatal opening, although, in general, the values of both parameters remained below those observed in the control plants.

Plant regeneration and genetic transformation of C. canadensis: a non-model plant appropriate for investigation of flower development in Cornus (Cornaceae)

KEY MESSAGE : Efficient Agrobacterium -mediated genetic transformation for investigation of genetic and molecular mechanisms involved in inflorescence architectures in Cornus species. Cornus canadensis is a subshrub species in Cornus, Cornaceae. It has recently become a favored non-model plant species to study genes involved in development and evolution of inflorescence architectures in Cornaceae. Here, we report an effective protocol of plant regeneration and genetic transformation of C. canadensis. We use young inflorescence buds as explants to efficiently induce calli and multiple adventitious shoots on an optimized induction medium consisting of basal MS medium supplemented with 1mg/l of 6-benzylaminopurine and 0.1mg/l of 1-naphthaleneacetic acid. On the same medium, primary adventitious shoots can produce a large number of secondary adventitious shoots. Using leaves of 8-week-old secondary shoots as explants, GFP as a reporter gene controlled by 35S promoter and hygromycin B as the selection antibiotic, a standard procedure including pre-culture of explants, infection, co-cultivation, resting and selection has been developed to transform C. canadensis via Agrobacterium strain EHA105-mediated transformation. Under a strict selection condition using 14mg/l hygromycin B, approximately 5% explants infected by Agrobacterium produce resistant calli, from which clusters of adventitious shoots are induced. On an optimized rooting medium consisting of basal MS medium supplemented with 0.1mg/l of indole-3-butyric acid and 7mg/l hygromycin B, most of the resistant shoots develop adventitious roots to form complete transgenic plantlets, which can grow normally in soil. RT-PCR analysis demonstrates the expression of GFP transgene. Green fluorescence emitted by GFP is observed in transgenic calli, roots and cells of transgenic leaves under both stereo fluorescence microscope and confocal microscope. The success of genetic transformation provides an appropriate platform to investigate the molecular mechanisms by which the various inflorescence forms are developed in Cornus plants.

Insights into panicoid inflorescence evolution

Inflorescence forms can be described by different combinatorial patterns of meristem fates (indeterminate versus determinate). In theory, the model predicts that any combination is possible. Whether this is true for grasses is unknown. In this paper, the subfamily Panicoideae s.s. (panicoid grasses) was chosen as the model group to investigate this aspect of grass inflorescence evolution. We have studied the inflorescence morphology of 201 species to complement information available in the literature. We have identified the most recurrent inflorescence types and character states among panicoids. Using multivariate approaches, we have indentified correlations among different inflorescence character states. By phylogenetic reconstruction methods we have inferred the patterns of panicoid inflorescence evolution. Our results demonstrate that not all theoretical combinatorial patterns of variation are found in panicoids. The fact that each panicoid lineage has a unique pattern of inflorescence evolution adds an evolutionary component to combinatorial model.

Leaf Development, Metamorphic Heteroblasty and Heterophylly in Berberis s. l. (Berberidaceae)

Shoot development of temperate and tropical members of Berberis s. l. was examined in order to assess: (1) the homology of the spines along the long shoots and the foliage leaves that form on the short shoots; (2) the occurrence of heterophylly and/or heteroblasty in the genus; and (3) the structural correspondence between cataphylls, spines, and foliage leaves. The 1-5-armed spines have been interpreted as modified compound leaves lacking stipules, as a modified lamina (central spine) with stipules (lateral spines), or less often, as transformed branches, or as epidermal outgrowths. On the other hand, the foliage leaves of the short shoots have been interpreted as leaflets of palmately compound leaves. Our results indicate that there are three distinct leaf types per node: (1) Leaves modified in spines spirally arranged in long shoots; (2) foliage, expanded leaves densely arranged in short shoots; and (3) cataphylls protecting axillary buds. The spines are leaf homologs with a clear distinction between the leaf base with stipules, and a laminar portion modified into the 1-5-armed spine; the lateral spines are not stipules as they arise from the marginal meristem of the laminar portion, and not from the leaf base. The foliage leaves also have stipules flanking the leaf base. Both spiny leaves and foliage leaves develop an articulation between the base and the laminar portion. Cataphylls of the short shoots of Berberis s. str. and those of the reproductive short shoots of Mahonia correspond to the entire leaf base, but those of the renewal (vegetative) shoots of Mahonia are spiny and have an odd vestigial pinnately compound lamina. Heterochrony due to ontogenetic truncation caused by the formation of the terminal inflorescence at the apex of the short shoots could be responsible for the lack of petiole/lamina differentiation in the foliage leaves. The spiny long-shoot/foliose short-shoot system of branching in Berberis s. str. appears to be genetically and phylogenetically fixed and not environment-dependent. This represents a clear example of metamorphic heteroblasty sensu Zotz et al. (Botanical Review 77:109–151, 2011) with further occurrence of heterophylly along the short shoots.

A somaclonal line SE7 of finger millet (Eleusine coracana) exhibits modified cytokinin homeostasis and increased grain yield

The SE7 somaclonal line of finger millet (Eleusine coracana) achieved increased grain yield in field trials that apparently resulted from a higher number of inflorescences and seeds per plant, compared with the wild type. Levels of endogenous cytokinins, especially those of highly physiologically active iso-pentenyl adenine, were increased during early inflorescence development in SE7 plants. Transcript levels of cytokinin-degrading enzymes but not of a cytokinin-synthesizing enzyme were also decreased in young leaves, seedlings, and initiating inflorescences of SE7. These data suggest that attenuated degradation of cytokinins in SE7 inflorescences leads to higher cytokinin levels that stimulate meristem activity and result in production of more inflorescences. Gene expression was compared between SE7 and wild-type young inflorescences using the barley 12K cDNA array. The largest fraction of up-regulated genes in SE7 was related to transcription, translation, and cell proliferation, cell wall assembly/biosynthesis, and to growth regulation of young and meristematic tissues including floral formation. Other up-regulated genes were associated with protein and lipid degradation and mitochondrial energy production. Down-regulated genes were related to pathogen defence and stress response, primary metabolism, glycolysis, and the C:N balance. The results indicate a prolonged proliferation phase in SE7 young inflorescences characterized by up-regulated protein synthesis, cytokinesis, floral formation, and energy production. In contrast, wild-type inflorescences are similar to a more differentiated status characterized by regulated protein degradation, cell elongation, and defence/stress responses. It is concluded that attenuated degradation of cytokinins in SE7 inflorescences leads to higher cytokinin levels, which stimulate meristem activity, inflorescence formation, and seed set.

Inflorescence and floral ontogeny in Crocus sativus L. (Iridaceae)

Inflorescence and floral ontogeny of the perennial, herbaceous crop Crocus sativus L. were studied using epi-illumination light microscopy. After production of leaves with helical arrangement a determinate inflorescence forms which becomes completely transformed into a single terminal flower. In some cases, bifurcation of the inflorescence meristem yields two or three floral meristems. The order of floral organs initiation is outer tepals – stamens – inner tepals – carpels. Stamens and outer tepals are produced from the lateral bifurcation of three common stamen-tepal primordia. Within each whorl, organs start developing unidirectionally from the adaxial side, except for the stamens which begin to grow from the abaxial side. Specialized features during organ development include interprimordial growth between tepals forming a perianth tube, fusion at the base of stamen filaments, and formation of an inferior ovary with unfused styles.

VEGETATIVE1 is essential for development of the compound inflorescence in pea.

Unravelling the basis of variation in inflorescence architecture is important to understanding how the huge diversity in plant form has been generated. Inflorescences are divided between simple, as in Arabidopsis, with flowers directly formed at the main primary inflorescence axis, and compound, as in legumes, where they are formed at secondary or even higher order axes. The formation of secondary inflorescences predicts a novel genetic function in the development of the compound inflorescences. Here we show that in pea this function is controlled by VEGETATIVE1 (VEG1), whose mutation replaces secondary inflorescences by vegetative branches. We identify VEG1 as an AGL79-like MADS-box gene that specifies secondary inflorescence meristem identity. VEG1 misexpression in meristem identity mutants causes ectopic secondary inflorescence formation, suggesting a model for compound inflorescence development based on antagonistic interactions between VEG1 and genes conferring primary inflorescence and floral identity. Our study defines a novel mechanism to generate inflorescence complexity.

The influence of cultivation method on the flowering of Salvia horminum L. 'Oxford Blue'

<i>Salvia horminum</i> L.) 'Oxford Blue' was grown from transplants or it was direct seeded. Four sowing dates were applied: 15 March or 30 March - in a greenhouse, in order to obtain transplants, 13 April, 27 April and 11 May - sown directly into the ground. Three plant densities were applied: 25 plants×m<sup>2</sup>, 16 plants×m<sup>2</sup>, 12 plants×m<sup>2</sup>. It was found that <i>Horminum</i> sage can be grown from transplants or direct seeded. The cultivation from transplants is more advantageous due to the earlier flowering of plants, by about two weeks, and a better quality of inflorescences evaluated in terms of their length and size of bracteoles. Direct sowing of <i>Horminum</i> sage at two-week intervals from the 2nd decade of April till the 2nd decade of May ensures that by the end of August mature inflorescence stems are obtained, ready for cutting. A delay in the date of sowing results in the development of significantly shorter inflorescence stems, irrespective of the plant density. Plant density does not affect significantly the length of the period of inflorescence formation and the date of flowering, but a larger spacing is favourable to plants growing big, what results in a larger fresh weight of the above-ground portion. Sage grown from transplants responses to favourable climatic conditions by the development of bigger inflorescences.

Teosinte Branched 1 modulates tillering in rice plants

Tillering is an important trait of cereal crops that optimizes plant architecture for maximum yield. Teosinte Branched 1 (TB1) is a negative regulator of lateral branching and an inducer of female inflorescence formation in Zea mays (maize). Recent studies indicate that TB1 homologs in Oryza sativa (rice), Sorghum bicolor and Arabidopsis thaliana act downstream of the auxin and MORE AUXILIARY GROWTH (MAX) pathways. However, the molecular mechanism by which rice produces tillers remains unknown. In this study, transgenic rice plants were produced that overexpress the maize TB1 (mTB1) or rice TB1 (OsTB1) genes and silence the OsTB1 gene through RNAi-mediated knockdown. Because lateral branching in rice is affected by the environmental conditions, the phenotypes of transgenic plants were observed in both the greenhouse and the paddy field. Compared to wild-type plants, the number of tillers and panicles was reduced and increased in overexpressed and RNAi-mediated knockdown OsTB1 rice plants, respectively, under both environmental conditions. However, the effect was small for plants grown in paddy fields. These results demonstrate that both mTB1 and OsTB1 moderately regulate the tiller development in rice.

Stylosanthes (Leguminosae-Papilionoideae-Dalbergiae) no estado de São Paulo, Brasil

Resumo Stylosanthes Sw. possui 48 espécies com distribuição pantropical. O gênero é membro do informal clado Pterocarpus - Dalbergióide. Este trabalho apresenta um estudo taxonômico do gênero Stylosanthes para o estado de São Paulo e foi realizado através de consulta de literatura especializada e exsicatas oriundas de herbários nacionais. Foram reconhecidas nove espécies: S. acuminata M.B. Ferreira & Sousa Costa, S. bracteata Vogel, S. capitata Vogel, S. humilis Kunth, S. gracilis Kunth, S. grandiflora M.B. Ferreira & Sousa Costa, S guianensis (Aubl.) Sw., S. scabra Vogel e S. viscosa Sw., diferenciadas principalmente pelo hábito, forma da inflorescência, número de artículos por lomento, aspecto do rostro nos lomentos e da semente. Descrições, ilustrações, comentários sobre afinidades entre as espécies, baseadas em morfologia e distribuição geográfica, e uma chave para o reconhecimento dos táxons são fornecidos.

The development of pistillate and perfect florets in Xeranthemum squarrosum (Asteraceae)

The formation of capitulum inflorescence with two different types of floret is an interesting issue in floral biology and evolution. Here we studied the inflorescence, floral ontogeny and development of the everlasting herb, Xeranthemum squarrosum, using epi-illumination microscopy. The small vegetative apex enlarged and produced involucral bracts with helical phyllotaxy, which subtended floret primordia in the innermost whorl. Initiation of floret primordia was followed by an acropetal sequence, except for pistillate peripheral florets. The origin of receptacular bracts was unusual, as they derived from the floral primordia rather than the receptacular surface. The order of whorl initiation in both disc and pistillate flowers included corolla, androecium and finally calyx, together with the gynoecium. The inception of sepals and stamens occurred in unidirectional order starting from the abaxial side, whereas petals incepted unidirectionally from the adaxial or abaxial side. Substantial differences were observed in flower structure and the development between pistillate and perfect florets. Pistillate florets presented a zygomorphic floral primordium, tetramerous corolla and androecium and two sepal lobes. In these florets, two sepal lobes and four stamen primordia stopped growing, and the ovary developed neither an ovule nor a typical stigma. The results suggest that peripheral pistillate florets in X.squarrosum, which has a bilabiate corolla, could be considered as an intermediate state between ancestral bilabiate florets and the derived ray florets.

Mobile Gibberellin Directly StimulatesArabidopsisHypocotyl Xylem Expansion

Secondary growth of the vasculature results in the thickening of plant structures and continuously produces xylem tissue, the major biological carbon sink. Little is known about the developmental control of this quantitative trait, which displays two distinct phases in Arabidopsis thaliana hypocotyls. The later phase of accelerated xylem expansion resembles the secondary growth of trees and is triggered upon flowering by an unknown, shoot-derived signal. We found that flowering-dependent hypocotyl xylem expansion is a general feature of herbaceous plants with a rosette growth habit. Flowering induction is sufficient to trigger xylem expansion in Arabidopsis. By contrast, neither flower formation nor elongation of the main inflorescence is required. Xylem expansion also does not depend on any particular flowering time pathway or absolute age. Through analyses of natural genetic variation, we found that ERECTA acts locally to restrict xylem expansion downstream of the gibberellin (GA) pathway. Investigations of mutant and transgenic plants indicate that GA and its signaling pathway are both necessary and sufficient to directly trigger enhanced xylogenesis. Impaired GA signaling did not affect xylem expansion systemically, suggesting that it acts downstream of the mobile cue. By contrast, the GA effect was graft transmissible, suggesting that GA itself is the mobile shoot-derived signal.

An Approach to the Characterization of Varietal Difference in Inflorescence Formation Due to Vernalization and Subsequent Photoperiod in Spring Seeding Turnip

カブの花房形成の品種間差異における低温処理期間と低温処理後の日長反応について, 花成強度を求めて検討した. 前報までに用いた‘耐病ひかり’を対照品種として, 現在のカブの春播き(晩抽性)経済品種8品種を用いて, 催芽種子に3℃で21～35日間低温処理を行った結果, 低温感応性が高い品種‘耐病ひかり’, ‘玉波’, ‘はくれい’, 低温感応性がやや低い品種‘健明’, ‘雪だるま’, 低温感応性が低い品種‘たかふじ’, ‘白鷹’, ‘福小町’, ‘CR白涼’の3つのタイプに分類することができると考えられた. 次に, 上記9品種のうち7品種を用いて, 催芽種子に3℃で14～35日間の低温処理後に8および24時間の日長処理を行った結果, いずれの品種でも, 8時間日長に比べて24時間日長で花房形成が促進された. さらに, 低温感応性が異なる3品種‘耐病ひかり’, ‘雪だるま’, ‘福小町’を用いて, 催芽種子に3℃で14～42日間の低温処理後に8, 12, 16および24時間の日長処理を行って低温と日長の花房形成に対する影響を検討した. ‘耐病ひかり’と同程度に花房形成するには, ‘雪だるま’では1週間, ‘福小町’では2週間以上‘耐病ひかり’よりも長く低温処理を要しており, 両品種の低温感応性は低いと考えられた. また, いずれの品種においても, 12時間日長に比べて, 8時間日長ではさらに長い低温処理で花房形成され, それに対して, 16時間日長で1週間あるいは1～2週間, 24時間日長で2週間それぞれ短い低温処理で花房形成されると考えられた. 以上のように, 春播き(晩抽性)とされる経済品種間においても低温感応性あるいは日長感応性の品種間差異は大きいと考えられた.

Long-day effects on the terminal inflorescence development of a photoperiod-sensitive soybean [Glycine max (L.) Merr.] variety

The type of terminal inflorescence is a key component for identifying soybean type. In this study, a late maturity and photoperiod-sensitive determinate soybean, cv. Zigongdongdou, was used to investigate effects of long-day (LD) on the formation and development of the terminal inflorescence. After emergence, soybean seedlings were subjected to 12h short-day (SD) photoperiod for 13 days to induce the initiation of terminal inflorescence. The plants were then moved to 16h LD treatment (LDT) for 0, 1, 2, 3, 4 and 5 wks, respectively. After LDT, plants were moved back to 12h SD condition until the end of the experiment. The LDT greatly affected morphological and anatomical features of terminal inflorescence as well as the developmental rate of plants. Reversed flowers could be found in the reversed “inflorescences” in plants with 2–5 wks LDT. Such changes were confirmed through morphological observation and anatomical dissection. In the long-day treatments, the formation of flowers and the development of terminal inflorescence could be reversed and plant type of a soybean could be further changed. This long-day effect was a cumulative process, which increased with the increase in the duration of LDT.

Influence of preculture treatment and types of explants on shoot growth and in vitro flowering of feathered amaranth (Celosia argentea var. plumose)

The shoots developed from both the shoot tip and nodal explants of feathered amaranth (Celosia argentea var. plumosa—feathered cockscomb or plumed cockscomb) after 8 weeks of culture in the presence of either paclobutrazol or benzyladenine (BA) were shorter than those developed on basal Murashige and Skoog (MS) medium (Physiol Plant, 15:473–497, 1962) alone. However, this retarding effect was more pronounced in the nodal explant culture. Shoot tip explants from 2-week-old seedlings were more adversely affected by 0.85 or 1.7 μM paclobutrazol than those from older seedlings. In contrast, regardless of preculture duration investigated nodal explants did not exhibit different response to three different concentrations of paclobutazol. The response to 2.2 or 4.4 μM BA appeared to be largely independent of the age of the shoot tip explants or preculture treatment of nodal explants. Shoots developed from nodal explants produced a higher number of terminal inflorescence than those from shoot tip explants. Moreover, only lateral shoots from nodal explant culture formed inflorescence. Increased preculture duration on basal MS medium could generally lessen the inhibitory effect of lower concentrations of paclobutazol or BA on terminal or lateral inflorescence formation in nodal explant culture.

Allelopathic interference of invasive Acacia dealbata Link on the physiological parameters of native understory species

The tree Acacia dealbata Link is an Australian woody legume that has become a serious environmental problem in Northwest Spain, where its expansion is assumed to reduce populations of native species and threaten local plant biodiversity. In order to investigate the potential involvement of allelopathic mechanisms in this process, net photosynthetic and respiration rates of four test native understory species (Hedera hibernica (G. Kirchn.) Bean, Dicranum sp., Dactylis glomerata L. and Leucobryum sp.) were evaluated using a Clark-type electrode in the presence of canopy leachate collected under A. dealbata stands at four times of the year for 2 years and macerate from their apical branches at the same sites and times. The first two test species were present both inside and outside of A. dealbata stands, while the last two were only located outside the stands. We found that there were significant differences in respiration and net photosynthetic rates between the control and A. dealbata extracts in all test species. The respiration rate was increased by both canopy leachate and macerate extracts on certain collection dates, but net photosynthetic rate was stimulated by macerate and inhibited by canopy leachate on other dates. The main phenological stages of A. dealbata in which respiration and net photosynthetic rates were more affected were blossoming, inflorescence formation and in periods after severe drought, in this decreasing order. Our results also showed that Dicranum sp., Leucobryum sp. and D. glomerata were more affected by aqueous extracts than other species during a 2-year period. We suggest that the observed inhibitory or stimulatory effects on the physiological parameters studied could have an adverse effect on the understory species, and that allelopathic interference seems to participate in this process.

Genome-wide identification and analysis of drought-responsive microRNAs in Oryza sativa

In addition to regulating growth and development, the most important function of microRNAs (miRNAs) in plants is the regulation of a variety of cellular processes underlying plant adaptation to environmental stresses. To gain a deep understanding of the mechanism of drought tolerance in rice, genome-wide profiling and analysis of miRNAs was carried out in drought-challenged rice across a wide range of developmental stages, from tillering to inflorescence formation, using a microarray platform. Among the 30 miRNAs identified as significantly down- or up-regulated under the drought stress, 11 down-regulated miRNAs (miR170, miR172, miR397, miR408, miR529, miR896, miR1030, miR1035, miR1050, miR1088, and miR1126) and eight up-regulated miRNAs (miR395, miR474, miR845, miR851, miR854, miR901, miR903, and miR1125) were revealed for the first time to be induced by drought stress in plants, and nine (miR156, miR168, miR170, miR171, miR172, miR319, miR396, miR397, and miR408) showed opposite expression to that observed in drought-stressed Arabidopsis. The most conserved down-regulated miRNAs were ath-miR170, the miR171 family, and ath-miR396, and the most conserved up-regulated miRNAs were ptc-miR474 and ath-miR854a. The identification of differentially expressed novel plant miRNAs and their target genes, and the analysis of cis-elements provides molecular evidence for the possible involvement of miRNAs in the process of drought response and/or tolerance in rice.

THE CIRCUMSCRIPTION, TAXONOMY AND BIOGEOGRAPHY OF PORTERANDIA (RUBIACEAE – GARDENIEAE)

The taxonomic history of Porterandia (Rubiaceae) is reviewed. Its plant architecture and other morphological characteristics are compared with those of the related Atractocarpus and Bungarimba. Porterandia species are typically gynodioecious (and sometimes gynomonoecious), with sexual dimorphism in inflorescence form and flowers. Secondary pollen presentation in bisexual flowers is present. In a cladistic analysis using 34 morphological characters, Porterandia, Atractocarpus heterophyllus (type species of Atractocarpus) and Bungarimba were neatly polarised from Aidia, the outgroup. The 20 species of Porterandia in the analysis formed a well-supported monophyletic group, clearly delimited by primary and lower-order branches with terminal cymes in forks, stipules fused into a tube and with hairy inner surfaces, anisophyllous leaf pairs, corollas with stiff bristle-like hairs over the tube outer surface and adaxially hairy lobes. A revision enumerated 22 species of Porterandia, including a new species, P. dinghoui Zahid & K.M.Wong. Borneo, with 19 species, is the centre of diversity; outlying taxa appear to diverge from Bornean taxa in some characters; for example, Porterandia anisophylla and P. scortechinii (Sumatra, Malaya) are the only species with downward-pointing hairs on the corolla tubes (the rest have upward-pointing hairs), and P. celebica (Sulawesi) has atypical hood-like, fused (instead of free) inflorescence bracts. The northwest Borneo region has a significant species diversity and congregation. Extinction of Porterandia populations from heavily disturbed or open sites indicates that habitat conservation and the integrity of large forest patches and tree stands are critical.