Endophyte Colonization Enhances Tolerance of Casuarina Equisetifolia to NaCl Stress by Modifying Osmoregulation, Antioxidant Enzymes, and Phytohormones

Background: Saline soils severely affect plant growth. Associations between endophytes and plants are known to significantly alter plant metabolism. This study reports the effects of a fungal endophyte species (Botryosphaeria ramosa ssp.) on osmoregulation, antioxidant enzymes, and the regulation of endogenous plant hormones in Casuarina equisetifolia under NaCl stress. C. equisetifolia plants, with and without B. ramosa ssp. colonization, were subjected to different levels of NaCl stress (0%, 5%, 10%, and 15%) for different amounts of time (0 d, 20 d, 40 d, and 60 d). Results: Antioxidant enzymes, phytohormones, and nutritive elements in the leaves and roots were determined. The results showed that colonization of the roots by B. ramosa ssp. improved the growth rate and dry weight of salt-stressed plants. Moreover, B. ramosa ssp. colonization increased the activities of superoxide dismutase, catalase, and peroxide but decreased the hydrogen peroxide content in the branches of C. equisetifolia under salt stress. Meanwhile, compared with non-colonized plants, endophyte colonization reduced the abscisic acid and proline contents but increased the contents of auxin, zeatin, and gibberellins. Importantly, the nutrient elements in the roots and branches of colonized plants were significantly different from those in the roots and branches of non-colonized plants under saline conditions. Conclusions: The results of this study showed that B. ramosa ssp. colonization can enhance the salt tolerance of C. equisetifolia. by improving the antioxidant enzyme content, regulating the phytohormones, and adjusting proline accumulation under NaCl stress.

KNOX protein KNAT1 regulates fruitlet abscission in litchi by repressing ethylene biosynthetic genes

Abscission is triggered by multiple environmental and developmental cues, including endogenous plant hormones. KNOTTED-LIKE HOMEOBOX (KNOX) transcription factors (TFs) play an important role in controlling abscission in plants. However, the underlying molecular mechanism of KNOX TFs in abscission is largely unknown. Here, we identified LcKNAT1, a KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1)-like protein from litchi, which regulates abscission by modulating ethylene biosynthesis. LcKNAT1 is expressed in the fruit abscission zone and its expression decreases during fruitlet abscission. Furthermore, the expression of the ethylene biosynthetic genes LcACS1, LcACS7, and LcACO2 increases in the fruit abscission zone, in parallel with the emission of ethylene in fruitlets. In vitro and in vivo assays revealed that LcKNAT1 inhibits the expression of LcACS/ACO genes by directly binding to their promoters. Moreover, ectopic expression of LcKNAT1 represses flower abscission in tomatoes. Transgenic plants expressing LcKNAT1 also showed consistently decreased expression of ACS/ACO genes. Collectively, these results indicate that LcKNAT1 represses abscission via the negative regulation of ethylene biosynthesis.

Reassessing the evolution of strigolactone synthesis and signalling

ABSTRACTStrigolactones (SLs) are an important class of carotenoid-derived signalling molecule in plants, which function both as exogenous signals in the rhizosphere, and as endogenous plant hormones. In flowering plants, SLs are synthesized by a core pathway of four enzymes, and are perceived by the DWARF14 (D14) receptor, leading to degradation of SMAX1-LIKE7 (SMXL7) target proteins in a manner dependent on the SCFMAX2 ubiquitin ligase. The evolutionary history of SLs is poorly understood, and it is not clear whether SL synthesis and signalling are present in all land plant lineages, nor when these traits evolved. We have utilized recently-generated genomic and transcriptomic sequences from across the land plant clade to resolve the origin of each known component of SL synthesis and signalling. We show that all enzymes in the core SL synthesis pathway originated at or before the base of land plants, consistent with the previously observed distribution of SLs themselves in land plant lineages. We also show that the late-acting enzyme LATERAL BRANCHING OXIDOREDUCTASE (LBO) is considerably more ancient than previously thought. We perform a detailed phylogenetic analysis of SMXL proteins, and show that specific SL target proteins only arose in flowering plants. We also assess diversity and protein structure in the SMXL family, identifying several previously unknown clades. Overall, our results suggest that SL synthesis is much more ancient than canonical SL signalling, consistent with the idea that SLs first evolved as rhizosphere signals, and were only recruited much later as hormonal signals.

Strigolactones in the Rhizosphere: Friend or Foe?

Strigolactones are well-known endogenous plant hormones that play a major role in planta by influencing different physiological processes. Moreover, ex planta, strigolactones are important signaling molecules in root exudates and function as host detection cues to launch mutualistic interactions with arbuscular mycorrhizal fungi in the rhizosphere. However, parasitic plants belonging to the Orobanchaceae family hijacked this communication system to stimulate their seed germination when in close proximity to the roots of a suitable host. As a result, the secretion of strigolactones by the plant can have both favorable and detrimental outcomes. Here, we discuss these dual positive and negative effects of strigolactones and we provide a detailed overview on the role of these molecules in the complex dialogs between plants and different organisms in the rhizosphere.

Ficus carica SSP Dottato Buds by Intercropping Different Species: Metabolites, Antioxidant Activity and Endogenous Plant Hormones (IAA, ABA)

Ficus carica is one of the most common tree crops in the Mediterranean basin. Its ethnobotanic use has been extensively studied to evaluate its biological activity in relation to the presence of specific secondary metabolites. In this paper, the extract of the gemstones of the ficus carica ssp dottato di Cosenza was studied with respect to different vegetation habitats (intercrops) and two different extraction techniques. Buds, in fact, are used in gemotherapy as macerated glycerides obtained by long extraction processes (21 Days).The use of a Dynamic extractor (Naviglio� Extractor) has allowed not only to reduce the extraction time (10 h) but to obtain a qualitatively and quantitatively enriched extract withactive ingredients to which the specific biological activity is reported. In fact, the total polyphenolic and total flavonoid components were determined, of which Quercetin-3O-Glucoside and 3-O-Rhamnoside were dosed, and the resulting anti-oxidant activity. IAA and ABA have also been quantified.