Inflorescence abscission protein SlIDL6 promotes low light intensity-induced tomato flower abscission.

In many fruiting plant species, flower abscission is induced by low light stress. Here, we elucidated how signaling mediated by the peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) controls low light-induced flower drop in tomato (Solanum lycopersicum). We analyzed the expression patterns of an IDA-Like gene (SlIDL6) during low light-induced flower abscission, and used tandem mass spectrometry to identify and characterize the mature SlIDL6 peptide. Tomato knockout lines were created to investigate the in vivo function of SlIDL6. In addition, yeast one-hybrid assays were used to investigate the binding of the SlWRKY17 transcription factor to the SlIDL6 promoter, and silencing of SlWRKY17 expression delayed low light-induced flower abscission. SlIDL6 was specifically expressed in the abscission zone and at high levels during low light-induced abscission and ethylene treatment. SlIDL6 knockout lines showed delayed low light-induced flower drop, and the application of SlIDL6 peptide accelerated abscission. Overexpression of SlIDL6 rescued the ida mutant phenotype in Arabidopsis (Arabidopsis thaliana), suggesting functional conservation between species. SlIDL6-mediated abscission was via an ethylene-independent pathway. We report a SlWRKY17-SlIDL6 regulatory module that functions in low light promoted abscission by increasing the expression of enzymes involved in cell wall remodeling and disassembly.

Induction of novel inflorescence traits in Chrysanthemum through 60Co gamma irradiation.

PURPOSE: The novelty in flower color or inflorescence form is recognized as a valuable trait in Chrysanthemum - a potential commercial flower crop with significant worth in global cut flower trade. This study was conducted to irradiate white and orange flowered cultivars of Chrysanthemum with an objective to identify and isolate desirable types representing novelty in flower color and inflorescence form from the irradiated populations. The terminal rooted cuttings of Chrysanthemum exposed to γ-irradiation at 10 or 15 Gy doses were found effective for inducing novel flower color variants in cultivars Thiching Queen and Purnima. The mutant progeny evolved with novel inflorescence traits of these cultivars will enrich the existing germplasm of Chrysanthemum for further utilization in breeding programs. MATERIALS AND METHODS: Two standard type Chrysanthemum cultivars, Thiching Queen and Purnima were exposed to varied doses of γ-rays (0, 5, 10, 15, and 20 Gy) using Cobalt 60 (60Co) as irradiation source for treating rooted cuttings. The irradiated mutant population was evaluated for likely variation in various vegetative and flowering characters compared to non-irradiated (control) plants. RESULTS: In Chrysanthemum cultivars Thiching Queen, seven and 'in Purnima', two flower color variants were isolated from the irradiated populations that were reportedly novel in color and desirable for commercial aspect. The leaf abnormalities were observed in mutant populations exhibiting variation in flower color, shape, and size of leaves. Certain floral abnormalities were also observed in inflorescence that reportedly progressed with increase in dosage of γ-rays irradiation. CONCLUSIONS: This study developed a gamma ray (60Co) induced mutagenesis protocol with potential application to develop novel and desirable mutants in Chrysanthemum.

Novel inflorescence architecture in gamma radiation-induced faba bean mutant populations.

Purpose: Inflorescence architecture is an important trait in the seed production of grain legumes. As several genes are responsible for this trait, any mutation, on these genes, may cause change in the inflorescence architecture. This study was conducted to evaluate inflorescence architecture in faba bean exposed to gamma radiation and to characterize the inflorescence architecture mutants phenotypically.Materials and methods: Faba bean M2 seeds (4898) generated from M1 generation of cultivars Hassawi 2 and ILB4347 were used in this study. M1 seeds were produced by irradiation treatments at two doses of gamma radiations (25 and 50 Gy). Faba bean M2 seeds were planted under field conditions. A total of 4032 mutant plants out of 4898 M2 seeds were evaluated for their inflorescence architecture.Results: A total of 20 determinate mutants were found and classified into four different types. Determinate type 1 was characterized by the formation of single terminal inflorescence on shoot apical meristem (SAM), type 2 by the formation of multiple inflorescences on SEM and generated upper branches that act as indeterminate type. Type 3 was characterized by the formation of a panicle-like inflorescence. While type 4 was characterized by the formation of primary and secondary panicle-like inflorescence. All of the determinate mutant types had shorter plant height and earlier maturity than control indeterminate type but had lower biological yield and seed yield. Among the determinate mutant types, determinate type 1 was only mutant that had a higher harvest index than the control indeterminate type. This promising mutant can be used to further breeding program to increase biological yield and seed yield.Conclusions: This study indicated potential of gamma radiation in inducing novel inflorescence architecture in faba bean. The mutants developed are valuable resources to study genes related to inflorescence architecture through forward genetics approach.

Differential UVR8 Signal across the Stem Controls UV-B-Induced Inflorescence Phototropism.

In the course of evolution, plants have developed mechanisms that orient their organs toward the incoming light. At the seedling stage, positive phototropism is mainly regulated by phototropin photoreceptors in blue and UV wavelengths. Contrasting with this, we report that UV RESISTANCE LOCUS8 (UVR8) serves as the predominant photoreceptor of UV-B-induced phototropic responses in Arabidopsis (Arabidopsis thaliana) inflorescence stems. We examined the molecular mechanisms underlying this response and our findings support the Blaauw theory (Blaauw, 1919), suggesting rapid differential growth through unilateral photomorphogenic growth inhibition. UVR8-dependent UV-B light perception occurs mainly in the epidermis and cortex, but deeper tissues such as endodermis can also contribute. Within stems, a spatial difference of UVR8 signal causes a transcript and protein increase of transcription factors ELONGATED HYPOCOTYL5 (HY5) and its homolog HY5 HOMOLOG at the UV-B-exposed side. The irradiated side shows (1) strong activation of flavonoid synthesis genes and flavonoid accumulation; (2) increased gibberellin (GA)2-oxidase expression, diminished GA1 levels, and accumulation of the DELLA protein REPRESSOR OF GA1; and (3) increased expression of the auxin transport regulator PINOID, contributing to diminished auxin signaling. Together, the data suggest a mechanism of phototropin-independent inflorescence phototropism through multiple, locally UVR8-regulated hormone pathways.

LAZY Genes Mediate the Effects of Gravity on Auxin Gradients and Plant Architecture.

A rice (Oryza sativa) mutant led to the discovery of a plant-specific LAZY1 protein that controls the orientation of shoots. Arabidopsis (Arabidopsis thaliana) possesses six LAZY genes having spatially distinct expression patterns. Branch angle phenotypes previously associated with single LAZY genes were here studied in roots and shoots of single and higher-order atlazy mutants. The results identify the major contributors to root and shoot branch angles and gravitropic behavior of seedling hypocotyls and primary roots. AtLAZY1 is the principal determinant of inflorescence branch angle. The weeping inflorescence phenotype of atlazy1,2,4 mutants may be due at least in part to a reversal in the gravitropism mechanism. AtLAZY2 and AtLAZY4 determined lateral root branch angle. Lateral roots of the atlazy2,4 double mutant emerged slightly upward, approximately 10° greater than perpendicular to the primary root axis, and they were agravitropic. Etiolated hypocotyls of the quadruple atlazy1,2,3,4 mutant were essentially agravitropic, but their phototropic response was robust. In light-grown seedlings, the root of the atlazy2,3,4 mutant was also agravitropic but when adapted to dim red light it displayed a reversed gravitropic response. A reversed auxin gradient across the root visualized by a fluorescent signaling reporter explained the reversed, upward bending response. We propose that AtLAZY proteins control plant architecture by coupling gravity sensing to the formation of auxin gradients that override a LAZY-independent mechanism that creates an opposing gravity-induced auxin gradient.

Influence of light and plant size on the reproduction and growth of small palm tree species: Comparing two methods for measuring canopy openness.

PREMISE OF THE STUDY: The reproduction and growth of large palms are influenced by many factors, including light and plant size, but few studies have examined smaller species (up to 2 m tall). We examined the effect of incident light and individual size on growth rates, the probability of reproduction, and the number of inflorescences of three small palm species and compared two methods for estimating canopy openness. METHODS: We measured canopy openness above the crowns of 132 adult plants and in the centers of 72 subplots (10 × 10 m) where individuals were sampled. We also recorded individual size and the number of leaves and inflorescences produced in two years. KEY RESULTS: Reproductive individuals of Butia paraguayensis tend to occur in illuminated microhabitats. Reproduction of Acrocomia emensis was correlated with stem diameter, but not with light. Reproduction was inversely related to individual size and light in Syagrus petraea, probably because this clonal palm invests heavily in sexual reproduction during its younger stages and clonal activity in older stages and may be adapted to the low-light conditions of the woodland understory. Growth was not predicted by light or individual size. Stronger correlations were found when incident light was measured directly above the crown, as opposed to the subplot center. CONCLUSIONS: The influences of light on reproduction are dependent on plant life histories, even among related and sympatric species. Light measurements directly above individual crowns provide better understanding of the reproductive effort rather than in subplot center.

High light exposure on seed coat increases lipid accumulation in seeds of castor bean (Ricinus communis L.), a nongreen oilseed crop.

Little was known on how sunlight affects the seed metabolism in nongreen seeds. Castor bean (Ricinus communis L.) is a typical nongreen oilseed crop and its seed oil is an important feedstock in industry. In this study, photosynthetic activity of seed coat tissues of castor bean in natural conditions was evaluated in comparison to shaded conditions. Our results indicate that exposure to high light enhances photosynthetic activity in seed coats and consequently increases oil accumulation. Consistent results were also reached using cultured seeds. High-throughput RNA-Seq analyses further revealed that genes involved in photosynthesis and carbon conversion in both the Calvin-Benson cycle and malate transport were differentially expressed between seeds cultured under light and dark conditions, implying several venues potentially contributing to light-enhanced lipid accumulation such as increased reducing power and CO2 refixation which underlie the overall lipid biosynthesis. This study demonstrated the effects of light exposure on oil accumulation in nongreen oilseeds and greatly expands our understanding of the physiological roles that light may play during seed development in nongreen oilseeds. Essentially, our studies suggest that potential exists to enhance castor oil yield through increasing exposure of the inflorescences to sunlight either by genetically changing the plant architecture (smart canopy) or its growing environment.

Expression of FcFT1, a FLOWERING LOCUS T-like gene, is regulated by light and associated with inflorescence differentiation in fig (Ficus carica L.).

BACKGROUND: Because the floral induction occurs in many plants when specific environmental conditions are satisfied, most plants bloom and bear fruit during the same season each year. In fig, by contrast, the time interval during which inflorescence (flower bud, fruit) differentiation occurs corresponds to the shoot elongation period. Fig trees thus differ from many species in their reproductive growth characteristics. To date, however, the molecular mechanisms underlying this unorthodox physiology of floral induction and fruit setting in fig trees have not been elucidated. RESULTS: We isolated a FLOWERING LOCUS T (FT)-like gene from fig and examined its function, characteristics, and expression patterns. The isolated gene, F. carica FT (FcFT1), is single copy in fig and shows the highest similarity at the amino acid level (93.1%) to apple MdFT2. We sequenced its upstream region (1,644 bp) and identified many light-responsive elements. FcFT1 was mainly expressed in leaves and induced early flowering in transgenic tobacco, suggesting that FcFT1 is a fig FT ortholog. Real-time reverse-transcription PCR analysis revealed that FcFT1 mRNA expression occurred only in leaves at the lower nodes, the early fruit setting positions. mRNA levels remained a constant for approximately 5 months from spring to autumn, corresponding almost exactly to the inflorescence differentiation season. Diurnal variation analysis revealed that FcFT1 mRNA expression increased under relative long-day and short-day conditions, but not under continuous darkness. CONCLUSION: These results suggest that FcFT1 activation is regulated by light conditions and may contribute to fig's unique fruit-setting characteristics.

Pleiotropic effects of ZmLAZY1 on the auxin-mediated responses to gravity and light in maize shoot and inflorescences.

Auxin has been found to control both gravitropism and inflorescence development in plant. Auxin transport has also been demonstrated to be responsible for tropism. Maize, a key agricultural crop, has distinct male (tassel) and female (ear) inflorescence, and this morphogenesis depends on auxin maximum and gradient. The classic maize mutant lazy plant1 (la1) has defective gravitropic response. The mechanism underlining maize gravitropism remains unclear. Recently, we isolated the ZmLA1 gene by map-based cloning, and our findings suggest that ZmLA1 might mediate the crosstalk between shoot gravitropism and inflorescence development by regulating auxin transport, auxin signaling, and auxin-mediated light response in maize. Here, we propose a model describing the ZmLA1-mediated complex interactions among auxin, gravity, light, and inflorescent development.

The CRYPTOCHROME1-dependent response to excess light is mediated through the transcriptional activators ZINC FINGER PROTEIN EXPRESSED IN INFLORESCENCE MERISTEM LIKE1 and ZML2 in Arabidopsis.

Exposure of plants to light intensities that exceed the electron utilization capacity of the chloroplast has a dramatic impact on nuclear gene expression. The photoreceptor Cryptochrome 1 (cry1) is essential to the induction of genes encoding photoprotective components in Arabidopsis thaliana. Bioinformatic analysis of the cry1 regulon revealed the putative cis-element CryR1 (GnTCKAG), and here we demonstrate an interaction between CryR1 and the zinc finger GATA-type transcription factors ZINC FINGER PROTEIN EXPRESSED IN INFLORESCENCE MERISTEM LIKE1 (ZML1) and ZML2. The ZML proteins specifically bind to the CryR1 cis-element as demonstrated in vitro and in vivo, and TCTAG was shown to constitute the core sequence required for ZML2 binding. In addition, ZML2 activated transcription of the yellow fluorescent protein reporter gene driven by the CryR1 cis-element in Arabidopsis leaf protoplasts. T-DNA insertion lines for ZML2 and its homolog ZML1 demonstrated misregulation of several cry1-dependent genes in response to excess light. Furthermore, the zml1 and zml2 T-DNA insertion lines displayed a high irradiance-sensitive phenotype with significant photoinactivation of photosystem II (PSII), indicated by reduced maximum quantum efficiency of PSII, and severe photobleaching. Thus, we identified the ZML2 and ZML1 GATA transcription factors as two essential components of the cry1-mediated photoprotective response.

Spider movement, UV reflectance and size, but not spider crypsis, affect the response of honeybees to Australian crab spiders.

According to the crypsis hypothesis, the ability of female crab spiders to change body colour and match the colour of flowers has been selected because flower visitors are less likely to detect spiders that match the colour of the flowers used as hunting platform. However, recent findings suggest that spider crypsis plays a minor role in predator detection and some studies even showed that pollinators can become attracted to flowers harbouring Australian crab spider when the UV contrast between spider and flower increases. Here we studied the response of Apis mellifera honeybees to the presence of white or yellow Thomisus spectabilis Australian crab spiders sitting on Bidens alba inflorescences and also the response of honeybees to crab spiders that we made easily detectable painting blue their forelimbs or abdomen. To account for the visual systems of crab spider's prey, we measured the reflectance properties of the spiders and inflorescences used for the experiments. We found that honeybees did not respond to the degree of matching between spiders and inflorescences (either chromatic or achromatic contrast): they responded similarly to white and yellow spiders, to control and painted spiders. However spider UV reflection, spider size and spider movement determined honeybee behaviour: the probability that honeybees landed on spider-harbouring inflorescences was greatest when the spiders were large and had high UV reflectance or when spiders were small and reflected little UV, and honeybees were more likely to reject inflorescences if spiders moved as the bee approached the inflorescence. Our study suggests that only the large, but not the small Australian crab spiders deceive their preys by reflecting UV light, and highlights the importance of other cues that elicited an anti-predator response in honeybees.

Quantitative analysis of carbon balance in the reproductive organs and leaves of Cinnamomum camphora (L.) Presl.

We investigated seasonal changes in dry mass and CO(2) exchange rate in fruit and leaves of the evergreen tree Cinnamomum camphora with the aim of quantitatively determining the translocation balance between the two organs. The fruit dry mass growth peaked in both August and October: the first increase was due to fruit pulp development and the second to seed development. Fruit respiration also increased with the rapid increase in fruit dry mass. Therefore, the carbohydrates required for fruit development showed two peaks during the reproductive period. Fruit photosynthesis was relatively high in early August, when fruit potentially re-fixed 75% of respired CO(2), indicating that fruit photosynthesis contributed 15-35% of the carbon requirement for fruit respiration. Current-year leaves completed their growth in June when fruit growth began. Current-year leaves translocated carbohydrates at a rate of approximately 10-25 mg dry weight (dw) leaf(-1) day(-1) into other organs throughout the entire fruit growth period. This rate of translocation from current-year leaves was much higher than the amount of carbohydrate required for reproduction (ca. 3 mg dw fruit(-1) day(-1)). Given the carbon balance between fruit and current-year leaves, carbohydrates for reproduction were produced within the current-year fruit-bearing shoots. C. camphora would be adaptive for steadily supplying enough amount of carbohydrate to the fruits, as there was little competition for carbohydrates between the two organs. As assimilates by leaves are used for processes such as reproduction and the formation of new shoots, photosynthesis by reproductive organs is considered to be important to compensate for reproductive cost.