Background Strigolactones (SLs) are important phytohormones that can regulate branch development in plants. Although SUPPRESSOR of MAX2 1-LIKE proteins (SMXLs) play a crucial role in SL signaling transduction, the SMXL gene family has not been well characterized in poplar. Results In this study, 12 members of the poplar SMXL gene family were identified and phylogenetically classified into four clades. Motif and 3D structural analyses revealed that PtSMXL proteins are structurally very conserved; however, the P-loop NTPase domain at the C-terminal was found to vary substantially among clades. A genomic collinearity analysis indicated that PtSMXL gene family members have expanded during recent genome doubling events in poplar, with all gene pairs subsequently undergoing purifying selection. According to a Cis-element analysis, PtSMXL promoters contain many light-responsive elements. In an expression pattern analysis, all 12 PtSMXL genes displayed tissue-specific expression, especially PtSMXL8a. PtSMXL7b expression was significantly downregulated after axillary bud growth begins. In addition, the expressions of PtSMXL7b and PtSMXL8a were highly induced by 2 μM GR24, a synthetic SL analog, thus suggesting that these genes are involved in SL-regulated axillary bud growth. In a yeast two-hybrid assay, only PtSMXL7b in clade II was able to interact with the SL receptor PtD14a in an SL dependent manner, which indicates that PtSMXL7b may be the functional homolog of D53/SMXL6/7/8 in poplar. Finally, we established its ability to affect axillary bud growth by constructing poplar overexpressing the PtSMXL7b gene. Conclusions Our findings may inform future research on the functions of SMXLs in poplar, especially with respect to branch development.
Understanding the adaptability of Chionanthus retusus Lindl. et Paxt. to extreme water conditions will help in exploring the potential application of this species in barren mountains. Three-year-old Chionanthus retusus seedlings were used in a greenhouse pot experiment that analyzed the effect of different moisture gradients on growth, photosynthetic and fluorescence characteristics, protective enzyme system, osmotic substance regulation and cell membrane damage. The results indicated that C. retusus can effectively grow at a relative soil water content of 44.6% and above and can maintain growth for 20 days under flooded conditions. Under drought stress, net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and intercellular carbon dioxide concentration (Ci) all showed a trend of gradual decrease. The trend of change was similar under waterlogging conditions. The maximal quantum yield of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ΦPSII), photochemical quenching coefficient (qP), and electron transport rate (ETR) all decreased as drought deepened. Malondialdehyde (MDA) content decreased first and then increased. However, superoxide dismutase (SOD) activity content, peroxidase (POD) activity content, and proline (Pro) activity content showed a trend of increasing and then decreasing. C. retusus had good adaptability in the slight drought treatment group and flooded treatment group but showed intolerance in the high drought group, which could still last for approximately 21 days. C. retusus was found to have a strong adaptability to water stress and can be used as an afforestation tree in barren mountains.
Chionanthus retusus is a deciduous shrub or small tree in the Oleaceae with important ornamental and economic value. In this study, fruits were collected from 22 individual C. retusus plants to study their morphological characteristics, oil content, and the contents and composition of fatty acids, phytosterols, and tocopherol. The average fruit fresh biomass, grain dry biomass, kernel dry biomass, and kernel percentage were 76.432 ± 20.75 g, 24.370 ± 6.52 g, 12.122 ± 3.21 g, and 50.16%, respectively. The average oil content of the kernels was 36.55%, ranging between 28.90% and 47.50%.The average total phytosterols content was 280.33 ± 43.96 mg/100 g. The average total tocopherols content was 578.31 ± 101.29 µg/g. In correlation analyses, the oil content was negatively correlated with the total phytosterols content (r = − 0.653, P < 0.01) and positively correlated with kernel weight (r = 0.762, P < 0.01). In principal component analyses, the first two principal components explained 77.1%,72.2%, and 91.2% of the total variance of fatty acid, phytosterol, and tocopherol composition, respectively. These results allowed us to identify germplasm resources with high oil yield, high oleic acid content, high phytosterol content, and high tocopherol content.
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