No abstract

The radiate sunflower inflorescence is composed by zygomorphic ray flowers and actinomorphic disk flowers. Studies performed on mutants identify HaCYC2c, a CYCLOIDEA (CYC)-like gene, as one of the key players controlling flower symmetry in sunflower. turf and tub mutants are characterized by a shift from zygomorphic to actinomorphic ray flowers, caused by insertion of transposable elements (TEs) in HaCYC2c gene. In dbl or Chry mutants, an insertion upstream the coding region of HaCYC2c causes the ectopic expression of the gene and the shift from actinomorphic to zygomorphic disk flowers. We focused on Chry2 mutant: a 1034 bp insertion placed 558 bp before the start codon of HaCYC2c was identified. The insertion is a truncated version of a CACTA TE. Unexpectedly, phenotypic and genetic co-segregation analysis in F2 and F3 progenies derived from the crosses Chry2 × turf and turf × Chry2 demonstrated that CACTA insertion is not always sufficient to alter the expression of HaCYC2c gene and generate Chry2 phenotype. F3 plants homozygous for the CACTA insertion displayed either HaCYC2c transcription pattern identical to wild-type plants or a normal heterogamous inflorescence. Stated these results, we conclude that a much more complex regulatory system stays behind the Chry2 phenotype.

What is fascinating in plants (true also in sessile animals such as corals and hydroids) is definitely their open and indeterminate growth, as a result of meristematic activity. Plants as well as animals are characterized by a multicellular organization, with which they share a common set of genes inherited from a common eukaryotic ancestor; nevertheless, circa 1.5 billion years of evolutionary history made the two kingdoms very different in their own developmental biology. Flowering plants, also known as angiosperms, arose during the Cretaceous Period (145-65 million years ago), and up to date, they count around 235,000 species, representing the largest and most diverse group within the plant kingdom. One of the foundations of their success relies on the plant-pollinator relationship, essentially unique to angiosperms that pushed large speciation in both plants and insects and on the presence of the carpel, the structure devoted to seed enclosure. A seed represents the main organ preserving the genetic information of a plant; during embryogenesis, the primary axis of development is established by two groups of pluripotent cells: the shoot apical meristem (SAM), responsible for gene rating all aboveground organs, and the root apical meristem (RAM), responsible for producing all underground organs. During postembryonic shoot development, axillary meristem (AM) initiation and outgrowth are responsible for producing all secondary axes of growth including inflorescence branches or flowers. The production of AMs is tightly linked to the production of leaves and their separation from SAM. As leaf primordia are formed on the flanks of the SAM, a region between the apex and the developing organ is established and referred to as boundary zone. Interaction between hormones and the gene network in the boundary zone is fundamental for AM initiation. AMs only develop at the adaxial base of the leaf; thus, AM initiation is also strictly associated with leaf polarity. AMs function as new SAMs: form axillary buds with a few leaves and then the buds can either stay dormant or develop into shoot branches to define a plant architecture, which in turn affects assimilate production and reproductive efficiency. Therefore, the radiation of angiosperms was accompanied by a huge diversification in growth forms that determine an enormous morphological plasticity helping plants to environmental changes. In this review, we focused on the developmental processes of AM initiation and outgrowth. In particular, we summarized the primary growth of SAM, the key role of positional signals for AM initiation, and the dissection of molecular players involved in AM initiation and outgrowth. Finally, the interaction between phytohormone signals and gene regulatory network controlling AM development was discussed.

Ascorbic acid (AA) is one of the most powerful\ud natural antioxidant able to prevent enzymatic browning after\ud exogenous treatment of minimally-processed products. The\ud specific mechanism by which AA prevents enzymatic\ud browning remains still debated and a direct effect of endogenous\ud AA stimulation and browning has never been studied.\ud The manipulation of AA pathway is a promising approach to\ud study the biochemicalmechanismbywhichAAacts as an antibrowning\ud agent. In this work, cDNA of L-galactono-1,4-lactone\ud dehydrogenase (L-GalLDH), one of the key gene of the\ud Smirnoff–Wheeler’s branch of AA biosynthetic pathway, was\ud isolated and overexpressed in lettuce (Lactuca sativa L. cv\ud ‘Iceberg’), a species highly prone to browning. The hypothesis\ud that the overexpression of L-GalLDH translates to AA accumulation\ud and reduces the browning phenomena in lettuce\ud leaves after cutting was tested. Our results indicate that\ud transgenic lettuce plants, showing about 19-fold overexpression\ud of L-GalLDHas compared towild type, had about?30 %\ud of AA concentration in mature leaves. Transgenic plants\ud exhibited reduced browning over the leaves, even 10 day after\ud cutting, as demonstrated by higher values of luminosity (L*)\ud and higher values of greenness (a*) compared to control\ud plants. Overall, these findings provide a first evidence of the\ud role of endogenous AA as browning-preventing agent. The\ud obtainment of T2 transgenic lettuce plants is a promising first\ud step to further determine the specificmechanismbywhichAA\ud acts as an anti-browning preservative

Axillary meristems (AMs) contribute to the growth of a plant, determining adult architecture and reproductive success in response to environmental stimuli. The missing flowers (mf ) mutant of sunflower (Helianthus annuus) is defective in AM development. mf lacks shoot branching and ray flowers, occasionally producing few disk flowers. Here we demonstrated that a point mutation in the REGULATOR OF AXILLARY MERISTEM FORMATION-LIKE (Ha-ROXL) gene of mf generates a premature stop codon and therefore a nonfunctional bHLH transcription factor, no longer localized in the nucleus, where it should exert its function. Virus-induced gene silencing of Ha-ROXL also causes defects in disk and ray flower development. Ha-ROXL mRNA accumulates at the adaxial boundaries of leaves and AMs. During inflorescence development, Ha-ROXL is expressed in small arcs of cells before a clear separation between abaxial bracts and disk flower primordia. No Ha-ROXL mRNA accumulates in mf inflorescences. Several genes known to play roles in plant architecture, auxin transport, and flower development are differentially expressed in mf and Ha-ROXL-silenced plants. These results highlight the predominant role of Ha-ROXL in regulating AMs in sunflower. In dicot, mf is the first mutant for which the ROXL gene is also required for initiation of flower meristems. K E Y W O R D S axillary meristems, bHLH transcription factor, floral meristems, Ha-ROXL, Helianthus annuus, in situ hybridization, missing flowers mutant, virus-induced gene silencing

No abstract

Artificial light at night (ALAN) is a globally spreading anthropogenic stressor, affecting more than 20% of coastal habitats. The alteration of the natural light/darkness cycle is expected to impact the physiology of organisms by acting on the complex circuits termed as circadian rhythms. Our understanding of the impact of ALAN on marine organisms is lagging behind that of terrestrial ones, and effects on marine primary producers are almost unexplored. Here, we investigated the molecular and physiological response of the Mediterranean seagrass, Posidonia oceanica (L.) Delile, as model to evaluate the effect of ALAN on seagrass populations established in shallow waters, by taking advantage of a decreasing gradient of dim nocturnal light intensity (from < 0.01 to 4 lx) along the NW Mediterranean coastline. We first monitored the fluctuations of putative circadian-clock genes over a period of 24 h along the ALAN gradient. We then investigated whether key physiological processes, known to be synchronized with day length by the circadian rhythm, were also affected by ALAN. ALAN influenced the light signalling at dusk/night in P. oceanica, including that of shorter blue wavelengths, through the ELF3–LUX1–ZTL regulatory network, and suggested that the daily perturbation of internal clock orthologs in seagrass might have caused the recruitment of PoSEND33 and PoPSBS genes to mitigate the repercussions of a nocturnal stress on photosynthesis during the day. A long-lasting impairment of gene fluctuations in sites characterised by ALAN could explain the reduced growth of the seagrass leaves when these were transferred into controlled conditions and without lighting during the night. Our results highlight the potential contribution of ALAN to the global loss of seagrass meadows, posing questions about key interactions with a variety of other human-related stressors in urban areas, in order to develop more efficient strategies to globally preserve these coastal foundation species.