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Phosphorus and nitrogen are essential nutrient elements that are needed by plants in large amounts. The arbuscular mycorrhizal symbiosis between plants and soil fungi improves phosphorus and nitrogen acquisition under limiting conditions. On the other hand, these nutrients influence root colonization by mycorrhizal fungi and symbiotic functioning. This represents a feedback mechanism that allows plants to control the fungal symbiont depending on nutrient requirements and supply. Elevated phosphorus supply has previously been shown to exert strong inhibition of arbuscular mycorrhizal development. Here, we address to what extent inhibition by phosphorus is influenced by other nutritional pathways in the interaction between Petunia hybrida and R. irregularis. We show that phosphorus and nitrogen are the major nutritional determinants of the interaction. Interestingly, the symbiosis-promoting effect of nitrogen starvation dominantly overruled the suppressive effect of high phosphorus nutrition onto arbuscular mycorrhiza, suggesting that plants promote the symbiosis as long as they are limited by one of the two major nutrients. Our results also show that in a given pair of symbiotic partners (Petunia hybrida and R. irregularis), the entire range from mutually symbiotic to parasitic can be observed depending on the nutritional conditions. Taken together, these results reveal complex nutritional feedback mechanisms in the control of root colonization by arbuscular mycorrhizal fungi.

Arrays of blue (B, 400-500 nm) and red (R, 600-700 nm) light-emitting diodes (LEDs) used for plant growth applications make visual assessment of plants difficult compared to a broad (white, W) spectrum. Although W LEDs are sometimes used in horticultural lighting fixtures, little research has been published using them for sole-source lighting. We grew seedlings of begonia (Begonia ×semperflorens), geranium (Pelargonium ×horturum), petunia (Petunia ×hybrida), and snapdragon (Antirrhinum majus) at 20°C under six sole-source LED lighting treatments with a photosynthetic photon flux density (PPFD) of 160 μmol∙m-2∙s-1 using B (peak = 447 nm), green (G, peak = 531 nm), R (peak = 660 nm), and/or mint W (MW, peak = 558 nm) LEDs that emitted 15% B, 59% G, and 26% R plus 6 μmol∙m-2∙s-1 of far-red radiation. The lighting treatments (with percentage from each LED in subscript) were MW100, MW75R25, MW45R55, MW25R75, B15R85, and B20G40R40. At the transplant stage, total leaf area, and fresh and dry weight were similar among treatments in all species. Surprisingly, when petunia seedlings were grown longer (beyond the transplant stage) under sole-source lighting treatments, the primary stem elongated and had flower buds earlier under MW100 and MW75R25 compared to under B15R85. The color rendering index of MW75R25 and MW45R55 were 72, and 77, respectively, which was higher than those of other treatments, which were ≤64. While photosynthetic photon efficacy of B15R85 (2.25 μmol∙J-1) was higher than the W light treatments (1.51-2.13 μmol∙J-1), the dry weight gain per unit electric energy consumption (in g∙kWh-1) of B15R85 was similar to those of MW25R75, MW45R55, and MW75R25 in three species. We conclude that compared to B+R radiation, W radiation had generally similar effects on seedling growth at the same PPFD with similar electric energy consumption, and improved the visual color quality of sole-source lighting.

In 1973, Jaffe identified and characterized the phenomenon of thigmomorphogenesis, also referred to as mechanical stress (MS) or mechanical stimulation in plants. Previous studies on petunia plants demonstrated that MS significantly affects growth dynamics. As a response to MS, petunias exhibit increased levels of indole-3-acetic acid (IAA) oxidase and peroxidase, although the active transport of endogenous IAA remains unaffected. Furthermore, earlier research has shown that MS inhibits the synthesis of IAA and gibberellin (GA 3 ), with noticeable effects on the 14th day of mechanical stimulation. The current experiment made on Petunia  ×  atkinsiana 'Pegasus Special Burgundy Bicolor’ focused on evaluating the morphological and physiological responses to MS, along with the expression of specific touch-responsive genes such as GH3.1, which is involved in auxin metabolism, and calmodulins (CaMs), playing an important role in stress responses. GH3.1 expression was found to be negatively correlated with IAA synthesis while positively correlated with GAs synthesis and IAA oxidase activity. Variable expression patterns were observed in the calmodulins: CAM53 and CAM81 expression positively correlated with IAA synthesis and plant height, whereas CAM72 expression was positively associated with GAs levels and IAA oxidase activity in plants touched 80× per day, but all of them were negatively related to IAA content and shoot increment, while positively related to GAs synthesis and IAA oxidase activity.

Petunias are renowned ornamental species widely cultivated as pot plants for their aesthetic appeal both indoors and outdoors. The preference for pot plants depends on their compact growth habit and abundant flowering. While genome editing has gained significant popularity in many crop plants in addressing growth and development and abiotic and biotic stress factors, relatively less emphasis has been placed on its application in ornamental plant species. Genome editing in ornamental plants opens up possibilities for enhancing their aesthetic qualities, offering innovative opportunities for manipulating plant architecture and visual appeal through precise genetic modifications. In this study, we aimed to optimize the procedure for an efficient genome editing system in petunia plants using the highly efficient multiplexed CRISPR/Cas9 system. Specifically, we targeted a total of six genes in Petunia which are associated with plant architecture traits, two paralogous of FLOWERING LOCUS T (PhFT) and four TERMINAL FLOWER-LIKE1 (PhTFL1) paralogous genes separately in two constructs. We successfully induced homogeneous and heterogeneous indels in the targeted genes through precise genome editing, resulting in significant phenotypic alterations in petunia. Notably, the plants harboring edited PhTFL1 and PhFT exhibited a conspicuously early flowering time in comparison to the wild-type counterparts. Furthermore, mutants with alterations in the PhTFL1 demonstrated shorter internodes than wild-type, likely by downregulating the gibberellic acid pathway genes PhGAI, creating a more compact and aesthetically appealing phenotype. This study represents the first successful endeavor to produce compact petunia plants with increased flower abundance through genome editing. Our approach holds immense promise to improve economically important potting plants like petunia and serve as a potential foundation for further improvements in similar ornamental plant species.

Petal fusion in petunia (Petunia x hybrida) results from lateral expansion of the five initially separate petal primordia, forming a ring-like primordium that determines further development. Here, we show that MAEWEST (MAW) and CHORIPETALA SUZANNE (CHSU) are required for petal and carpel fusion, as well as for lateral outgrowth of the leaf blade. Morphological and molecular analysis of maw and maw chsu double mutants suggest that polarity defects along the adaxial/abaxial axis contribute to the observed reduced lateral outgrowth of organ primordia. We show that MAW encodes a member of the WOX (WUSCHEL-related homeobox) transcription factor family and that a partly similar function is redundantly encoded by WOX1 and PRESSED FLOWER (PRS) in Arabidopsis thaliana, indicating a conserved role for MAW/WOX1/PRS genes in regulating lateral organ development. Comparison of petunia maw and Arabidopsis wox1 prs phenotypes suggests differential recruitment of WOX gene function depending on organ type and species. Our comparative data together with previous reports on WOX gene function in different species identify the WOX gene family as highly dynamic and, therefore, an attractive subject for future evo-devo studies.

Carotenoids and carotenoid cleavage products play an important and integral role in plant development. The Decreased apical dominance1 (Dad1)/PhCCD8 gene of petunia (Petunia hybrida) encodes a hypothetical carotenoid cleavage dioxygenase (CCD) and ortholog of the MORE AXILLARY GROWTH4 (MAX4)/AtCCD8 gene. The dad1-1 mutant allele was inactivated by insertion of an unusual transposon (Dad-one transposon), and the dad1-3 allele is a revertant allele of dad1-1. Consistent with its role in producing a graft-transmissible compound that can alter branching, the Dad1/PhCCD8 gene is expressed in root and shoot tissue. This expression is upregulated in the stems of the dad1-1, dad2, and dad3 increased branching mutants, indicating feedback regulation of the gene in this tissue. However, this feedback regulation does not affect the root expression of Dad1/PhCCD8. Overexpression of Dad1/PhCCD8 in the dad1-1 mutant complemented the mutant phenotype, and RNA interference in the wild type resulted in an increased branching phenotype. Other differences in phenotype associated with the loss of Dad1/PhCCD8 function included altered timing of axillary meristem development, delayed leaf senescence, smaller flowers, reduced internode length, and reduced root growth. These data indicate that the substrate(s) and/or product(s) of the Dad1/PhCCD8 enzyme are mobile signal molecules with diverse roles in plant development.

Up till now, despite of well-developed ornamental market, very little information is available on Petunia hybrida L. tolerance against heavy metals (HMs), which can contribute in both beautification of urban dwellings, as well as potential in phytoremediation. Therefore, hydroponic study was conducted to check the effects of Cd, Cr, Cu, Ni and Pb individually (50 and 100 μM) and with co-application of EDTA (2.5 mM) in Hoagland’s nutrient solution. Results indicated higher uptake of Cd, Cr, Ni and Pb in above ground parts, and Cu in roots, further the co-application of EDTA enhanced HMs uptake in P. hybrida L. This uptake accompanied changes in biochemical stress indicators, included significantly higher MDA, H 2 O 2 contents and electrolyte leakage with reduced chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content. Upon exposure to HMs increased antioxidant enzyme activities (CAT, POX, GST, APX, and SOD) were noted. Though selected HMs can be removed by using P. hybrida L., the findings of current study indicated that the direct exposure of P. hybrida L. to Cd, Cr, Cu, Ni and Pb damaged the plant’s aesthetics, and to use P. hybrida L. for beautification of urban landscape or phytoremediation, appropriate soil modification should be included.

The ARF gene family plays a vital role in regulating multiple aspects of plant growth and development. However, detailed research on the role of the ARF family in regulating flower development in petunia and other plants remains limited. This study investigates the distinct roles of PhARF5 and PhARF19a in Petunia hybrida flower development. Phylogenetic analysis identified 29 PhARFs, which were grouped into four clades. VIGS-mediated silencing of PhARF5 and PhARF19a led to notable phenotypic changes, highlighting their non-redundant functions. PhARF5 silencing resulted in reduced petal number and limb abnormalities, while PhARF19a silencing disrupted corolla tube formation and orientation. Both genes showed high expression in the roots, leaves, and corollas, with nuclear localization. The transcriptomic analysis revealed significant overlaps in DEGs between PhARF5 and PhARF19a silencing, indicating shared pathways in hormone metabolism, signal transduction, and stress responses. Phytohormone analysis confirmed their broad impact on phytohormone biosynthesis, suggesting involvement in complex feedback mechanisms. Silencing PhARF5 and PhARF19a led to differential transcription of numerous genes related to hormone signaling pathways beyond auxin signaling, indicating their direct or indirect crosstalk with other phytohormones. However, significant differences in the regulation of these signaling pathways were observed between PhARF5 and PhARF19a. These findings reveal the roles of ARF genes in regulating petunia flower development, as well as the phylogenetic distribution of the PhARFs involved in this process. This study provides a valuable reference for molecular breeding aimed at improving floral traits in the petunia genus and related species.

To attract insects, flowers produce nectar, an energy-rich substance secreted by specialized organs called nectaries. For Arabidopsis thaliana, a rosid species with stamen-associated nectaries, the floral B-, C-, and E- functions were proposed to redundantly regulate nectary development. Here we investigated the molecular basis of carpel-associated nectary development in the asterid species Petunia hybrida. We show that its euAGAMOUS (euAG) and PLENA (PLE) C-lineage MADS-box proteins are essential for nectary development, while their overexpression is sufficient to induce ectopic nectaries on sepals. Furthermore, we demonstrate that Arabidopsis nectary development also fully depends on euAG/PLE C-lineage genes. In turn, we show that petunia nectary development depends on two homologs of CRABS CLAW (CRC), a gene previously shown to be required for Arabidopsis nectary development, and demonstrate that CRC expression in both species depends on the members of both euAG/PLE C-sublineages. Therefore, petunia and Arabidopsis employ a similar molecular mechanism underlying nectary development, despite otherwise major differences in the evolutionary trajectory of their C-lineage genes, their distant phylogeny and different nectary positioning. However, unlike in Arabidopsis, petunia nectary development is position-independent within the flower. Finally, we show that the TARGET OF EAT (TOE)-type BLIND ENHANCER (BEN) and APETALA2 (AP2)-type REPRESSOR OF B-FUNCTION (ROB) genes act as major regulators of nectary size.

Plants alter their development in response to changes in their environment. This responsiveness has proven to be a successful evolutionary trait. Here, we tested the hypothesis that two key environmental factors, light and nutrition, are integrated within the axillary bud to promote or suppress the growth of the bud into a branch. Using petunia (Petunia hybrida) as a model for vegetative branching, we manipulated both light quality (as crowding and the red-to-far-red light ratio) and phosphate availability, such that the axillary bud at node 7 varied from deeply dormant to rapidly growing. In conjunction with the phenotypic characterization, we also monitored the state of the strigolactone (SL) pathway by quantifying SL-related gene transcripts. Mutants in the SL pathway inhibit but do not abolish the branching response to these environmental signals, and neither signal is dominant over the other, suggesting that the regulation of branching in response to the environment is complex. We have isolated three new putatively SL-related TCP (for Teosinte branched1, Cycloidia, and Proliferating cell factor) genes from petunia, and have identified that these TCP-type transcription factors may have roles in the SL signaling pathway both before and after the reception of the SL signal at the bud. We show that the abundance of the receptor transcript is regulated by light quality, such that axillary buds growing in added far-red light have greatly increased receptor transcript abundance. This suggests a mechanism whereby the impact of any SL signal reaching an axillary bud is modulated by the responsiveness of these cells to the signal.