Attainment of reproductive competence, phase transition, and quantification of juvenility in mutant genetic screens

Plant development between seedling emergence and flowering is characterized by a series of successive qualitative phases: (1) a post embryonic photoperiodinsensitive phase, during which plants are insensitive to photoperiod; (2) a photoperiod- sensitive inductive phase, in which plants require a number of short day (SD) or long day (LD) inductive cycles, depending on their age for rapid flowering, and (3) a photoperiod-insensitive post-inductive phase, in which plant development is no longer influenced by photoperiod (Figure 1; Matsoukas et al., 2013)

Direct and indirect selection on flowering time, water-use efficiency (WUE, δ (13)C), and WUE plasticity to drought in Arabidopsis thaliana.

Flowering time and water-use efficiency (WUE) are two ecological traits that are important for plant drought response. To understand the evolutionary significance of natural genetic variation in flowering time, WUE, and WUE plasticity to drought in Arabidopsis thaliana, we addressed the following questions: (1) How are ecophysiological traits genetically correlated within and between different soil moisture environments? (2) Does terminal drought select for early flowering and drought escape? (3) Is WUE plasticity to drought adaptive and/or costly? We measured a suite of ecophysiological and reproductive traits on 234 spring flowering accessions of A. thaliana grown in well-watered and season-ending soil drying treatments, and quantified patterns of genetic variation, correlation, and selection within each treatment. WUE and flowering time were consistently positively genetically correlated. WUE was correlated with WUE plasticity, but the direction changed between treatments. Selection generally favored early flowering and low WUE, with drought favoring earlier flowering significantly more than well-watered conditions. Selection for lower WUE was marginally stronger under drought. There were no net fitness costs of WUE plasticity. WUE plasticity (per se) was globally neutral, but locally favored under drought. Strong genetic correlation between WUE and flowering time may facilitate the evolution of drought escape, or constrain independent evolution of these traits. Terminal drought favored drought escape in these spring flowering accessions of A. thaliana. WUE plasticity may be favored over completely fixed development in environments with periodic drought

Circular 91

Plants of Begonia x tuberhybrida ‘Nonstop’, ‘Clips’, and ‘Musical’ were exposed to 1, 2, 3, or 4 weeks of short days (SD, 9 hours day length) initiated at 3 stages of plant development (immediately upon germination, 4 or 8 weeks after germination). Prior to and succeeding short days, plants were exposed to long days (LD, 16 hours day length). Musical flowered on average 68 days, Clips 78 days and Nonstop 83 days after germination under continuous LD conditions. In Nonstop, SD for 1, 2, 3, or 4 weeks delayed plant development by an average 12 days compared to LD grown plants. One, 2, or 3 weeks of SD resulted in 1 week slower flowering and 4 weeks of SD resulted in 2 weeks later flowering in Clips. The sensitivity to SD varied with plant stage in Musical. Three or 4 weeks of SD initiated at germination or 4 weeks after germination resulted in an average delayed flowering of 13 days compared to LD plants. SD initiated 8 weeks after germination had no effect on rate of development in Musical

Floral induction and development in Myosotidium hortensia and Phormium cookianum : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, New Zealand

Little is known of the stimuli needed for flowering in two New Zealand endemic plants, Myosotidium hortensia and Phormium cookianum. These plants are widely recognised by the horticulture sector and the concerns of this thesis were to aid understanding of floral induction and development in the two species. Environmental stimuli were investigated by growing plants under factorial combinations of daylength and temperature in controlled growth rooms. The two daylengths used, termed long days (LD) and short days (SD), consisted of night / day periods of 8 / 16 h und 16/8 h respectively. Two night / day temperature regimes of 4 / 7°C and 18 / 24°C referred to as Cold and Warm respectively, were combined with the daylengths to make four treatments. Floral induction in both species was unaffected by temperature or daylength, with approximately 50% of the P. cookianum flowering under all environmental treatments. M. hortensia did not flower. The absence of flowering seen in half of the P. cookianum plants was associated with a small size (fewer nodes at the commencement of the environmental treatments). Floral development in those plants that did flower was accelerated in P. cookianum by eight weeks growth under Cold compared with Warm treatment. Floral development of P. cookianum was further enhanced by four weeks treatment at Cold temperatures followed by transfer for four weeks at Warm temperatures. Vegetative growth was enhanced under Warm temperatures compared with Cold, in both P. cookianum and M. hortensia. Hormonal floral stimuli were investigated by application of the gibberellin A 3 , followed by growth under Cold SD conditions. The proportion of plants flowering was increased by GA 3 in P. cookianum. GA 3 -treaied P. cookianum flowered with fewer nodes as GA 3 concentration increased. In M. hortensia, GA 3 application did not cause flowering although stem elongation was increased. A region of the P. cookianum FLORICAULA / LEAFY (FLO/LFY) homologue (PFL) mRNA was isolated by reverse transcriptase-PCR and sequenced, and shown to share strong sequence identity with other FLO/LFY-like genes. PFL mRNA expression was compared with levels of actin mRNA using Real Time reverse transcriptase-PCR, performed using a LightCycler and the double stranded DNA binding dye SYBR Green 1. Upregulation of PFL mRNA at the meristem occurred over time, and increases coincided with changes in morphology from vegetative to inflorescence development. As predicted, greater PFL expression was observed in fans of larger size, these being the fans with greater likelihood of flowering

Evaluating the Potential of Using 5-Azacytidine as an Epimutagen

A number of early flowering lines were induced when 5-azacytidine was applied to germinating flax (Linum usitatissimum L.) seed. The genetics of these lines indicate that the induced changes are epigenetic and probably result from demethylation of the genomic DNA at loci that affect flowering age. Although the growth and development of three stable early flowering lines are altered and the percentage of filled seed was reduced in all three lines compared with controls, measures of seed productivity demonstrated that harvest index was unaffected in two of the lines. In the third, harvest index was lower than normal and both seed set per capsule and seed mass per 100 seed were reduced. Furthermore, six generations after induction this line began to display relatively high levels of polyembryony. The late appearance of this twinning and other aspects related to working with lines induced by 5-azacytidine and using 5-azacytidine as an epimutagen are discussed

The photoperiodic control of growth and development of Chenopodium Rubrum L. plants in vitro

Influence of the photoperiod on growth, flowering, and seed development in vitro of Chenopodium rubrum L., a short day annual, was examined. Chenopodium rubrum plants modify their growth and reproductive development in accordance with the photoperiod. With an increase of day length, growth was stimulated, flowering was delayed, seed development occurred earlier, and the plants produced more seeds. By altering photoperiods during induction and evocation of flowering, it is shown that the photoperiod experienced by seedlings during early reproductive development determines the pattern of plant growth to the end of ontogenesis, the time to flowering, and the course of seed development. It is therefore concluded that growth and reproductive development of C. rubrum are photoperiod-sensitive to during a precise short part of its life cycle

Mechanisms regulating inflorescence development and flowering traits in Arabis alpina, an alpine perennial

Flowering and inflorescence development are important plant processes that determine reproductive success, thus survival of many plant species. These processes are controlled by both endogenous and environmental cues. Arabis alpina, an alpine perennial and a close relative of the annual species Arabidopsis thaliana, initiates flower buds during prolonged cold exposure. Flower emergence then occurs a season later during permissive growth conditions. The Pajares accession of A. alpina was used in this study to investigate cold duration effects. Extended vernalization accelerated flower emergence, increased the percentage of flowering inflorescence branches and suppressed floral reversion within the inflorescence. The A. alpina gene, PERPETUAL FLOWERING 1 (PEP1) is a floral repressor that contributes to perennial traits and the orthologue of the A. thaliana gene, FLOWERING LOCUS C (FLC). The pep1 mutant does not require vernalization to flower and exhibits compromised perennial traits. Second site enhancer mutants of pep1-1, enhancers of perpetual flowering 1 (eop), were isolated to identify additional regulators of flowering. Five selected mutants are characterized here for their early flowering and inflorescence phenotypes. One mutant, eop101, developed a determinate inflorescence with a terminal flower as it carried lesion in the A. alpina TERMINAL FLOWER 1. Genome wide transcriptome analysis on this mutant revealed the up regulation of some flower meristem and organ identity genes and transcription factors associated with regulation of circadian rhythms and flowering. The causal gene of the other eops has been identified as a member of an AAA+ ATPase family whose involvement in flowering and inflorescence development has so far not been reported. Characterization of eop in a PEP1 background using introgression lines (ILs), revealed EOP to be involved in flowering and inflorescence development in response to vernalization duration. ILs exhibited early saturation of vernalization requirement to accelerate flowering, reduced floral reversion and increased percentage of flowering branches. Furthermore, transcriptome analysis suggests the involvement of EOP in stress response, reproductive development and transport of lipids and oligopeptides

Activities of antioxidative enzymes during Chenopodium rubrum L. ontogenesis in vitro

For the short-day plant Chenopodium rubrum, a 14 h/10 h photoperiod is inductive for flowering, while continuous light (CL) is noninductive. Plants of one group were grown continuously under ail inductive photoperiod, while in the other group flowering induction was delayed by 17 days of CL in order to separate oil the time scale different developmental phases in plants of the same age. Regardless of the photoperiodic conditions the plants were exposed to, seed maturation occurred in 10 weeks. Activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) were determined in different phases of development (vegetative growth, flowering, seed development, and maturation). The activities of antioxidative enzymes depended on both the phase of development and the photoperiod. In plants grown continuously under an inductive photoperiod, high CAT and POD activities were detected at the time of flowering and decreased during seed development and maturation. In plants in which flowering induction was delayed by 17 days of CL, the activities of POD and SOD were lowest in the vegetative phase of development and attained maximum values in the phase of seed maturation. In both groups of plants, the highest CAT activity was measured at the time of flowering

Floral induction and flower formation : the role and potential applications of miRNAs

The multiple regulatory pathways controlling flowering and flower development are varied and complex, and they require tight control of gene expression and protein levels. MicroRNAs (miRNAs) act at both the transcriptional and post-transcriptional level to regulate key genes involved in flowering-related processes such as the juvenile–adult transition, the induction of floral competence and flower development. Many different miRNA families are involved in these processes and their roles are summarized in this review, along with potential biotechnological applications for miRNAs in controlling processes related to flowering and flower development