Prolonged exposure to cold temperatures often results in a relatively low flowering rate in litchi (Litchi chinensis Sonn.) trees with younger leaves. This study aimed to verify the impact of stem girdling on litchi flowering by identifying and characterizing the induced metabolic changes. After a 60 day exposure to cold treatment at 15 °C/10 °C (12 h/12 h), the flowering rate of the girdled trees was 100%, while that of the non-girdled trees was 20%, indicating that girdling improved litchi flowering at its turning stage. The metabolic profiles of litchi leaves with and without stem girdling during floral induction were compared and 505 metabolites potentially associated with litchi flowering were detected. Most metabolites were involved in the metabolism of starch and sucrose, fatty acid, and phenylpyruvic acid. The metabolic pathways concerned with the biosynthesis of epinephrine, sucrose, and d-maltose were induced in leaves after girdling treatment. The level of galactitol, phenylpyruvic acid, acetyl-CoA, linoleic acid, alpha-linolenic acid, and 13-HPOT biosynthesis remained stable in the leaves from girdled trees but changed drastically in the leaves from non-girdled trees. In addition, 379 metabolites concerning flowering rate were characterized. Metabolism pathways of starch and sucrose, galactose, and linoleic acid are of great significance to the flowering of litchi. Linoleic acid exhibited the most significant variations between girdled trees and non-girdled trees with fold changes of up to 13.62. These results contribute to understanding the biological mechanism of litchi floral induction and the metabolic changes after stem girdling.

ES5-4^T, a Gram-positive, motile, aerobic, and rod-shaped strain, was isolated from the rhizosphere of Galinsoga parviflora growing in the selenium-rich ore area of Enshi, Hubei Province, China. This strain can grow at pH levels of 5.0–10.0 and temperatures of 4–42 °C, with optimal growth at pH 7.0 and 28 °C. It was found to resist NaCl up to 5% (w/v), with an optimal growth condition of 0.5–1.0%. The strain exhibited tolerance to selenite (Se⁴⁺) concentrations up to 5000 mg/L. The major fatty acids of the ES5-4^T strain were anteiso-C_15:0 (46.5%) and C_16:0 (21.7%), its predominant respiratory quinone was MK-7, and its polar lipids included diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and an unidentified phospholipid (PL). The presence of the 16S rRNA gene sequence implies that ES5-4^T belongs to a member of the genus Paenibacillus, with the highest sequence similarity of 98.4% to Paenibacillus pabuli NBRC 13638^T. The bac120 tree also confirmed that the strain is within the genus Paenibacillus. The average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between ES5-4^T and closely related members of the genus Paenibacillus were all below the cutoff levels of 95–96% and 70%, respectively. Based on a polyphasic approach, including phenotypic, chemotaxonomic, and phylogenetic analyses, the ES5-4^T strain is proposed as a novel species of the genus Paenibacillus, for which the name Paenibacillus hubeiensis sp. nov. is proposed. This type strain is designated as ES5-4^T (=GDMCC 1.3540^T = KCTC 43478^T).

In perennial fruit trees, erratic floral initiation and alternate bearing represent major horticultural challenges, yet how vegetative shoot maturity conditions low-temperature responsiveness remains poorly understood. Here, using litchi (Litchi chinensis Sonn.) as a model, we deciphered the physiological and molecular framework governing maturity-dependent floral induction under winter chilling. Mature terminal shoots exhibited exceptional flowering competence and superior inflorescence morphology, whereas immature expanding shoots failed to initiate pure panicles. Dynamic metabolic profiling revealed that shoot maturation established a high-energy status characterized by elevated sucrose accumulation and sustained transcription of trehalose-6-phosphate synthase genes (LcTPS1/3/4). At the transcriptional level, specific members of LcSPL1, LcSPL3, and LcSPL10 were strongly upregulated in mature shoots, reaching peak expression at the “whitish millet” stage, marking morphological flower bud differentiation. Functional characterization in Arabidopsis thaliana confirmed that ectopic expression of LcSPL1/3/10 significantly accelerated flowering time and reduced rosette leaf number. Mechanistically, dual-luciferase reporter assays demonstrated that LcSPL1, LcSPL3, and LcSPL10 transcriptionally activated the promoter of the florigen gene LcFT1, with LcSPL1 exerting the strongest transactivation, whereas the immature shoot-enriched LcSPL9 repressed LcFT1 expression. Concurrently, mature leaves exhibited a dramatic surge in LcFT1 transcript levels alongside persistent suppression of the floral repressor LcTFL1. Together, our findings demonstrate that shoot maturity confers floral competence through an integrated T6P metabolism and LcSPL1/3/10–LcFT1 transcriptional cascade. This study provides crucial theoretical insights and potential targets for flowering-related regulation in perennial woody crops.

In perennial fruit trees, erratic floral initiation and alternate bearing represent major horticultural challenges, yet how vegetative shoot maturity conditions low-temperature responsiveness remains poorly understood. Here, using litchi (Litchi chinensis Sonn.) as a model, we deciphered the physiological and molecular framework governing maturity-dependent floral induction under winter chilling. Mature terminal shoots exhibited exceptional flowering competence and superior inflorescence morphology, whereas immature expanding shoots failed to initiate pure panicles. Dynamic metabolic profiling revealed that shoot maturation established a high-energy status characterized by elevated sucrose accumulation and sustained transcription of trehalose-6-phosphate synthase genes (LcTPS1/3/4). At the transcriptional level, specific members of the LcSPL1, LcSPL3, and LcSPL10 were strongly upregulated in mature shoots, reaching peak expression at the "whitish millet" stage marking morphological flower bud differentiation. Functional characterization in Arabidopsis thaliana confirmed that ectopic expression of LcSPL1/3/10 significantly accelerated flowering time and reduced rosette leaf number. Mechanistically, dual-luciferase reporter assays demonstrated that LcSPL1, LcSPL3, and LcSPL10 directly transactivated the promoter of the florigen gene LcFT1, with LcSPL1 exerting the strongest transactivation, whereas the immature shoot-enriched LcSPL9 repressed LcFT1 expression. Concurrently, mature leaves exhibited a dramatic surge in LcFT1 transcript levels alongside persistent suppression of the floral repressor LcTFL1. Together, our findings demonstrate that shoot maturity confers floral competence through an integrated T6P metabolism and LcSPL1/3/10–LcFT1 transcriptional cascade, providing crucial theoretical insights and actionable targets for mitigating alternate bearing in perennial woody crops.

A Gram-stain-positive, motile, aerobic, rod-shaped strain ES5-4T was isolated from the rhizosphere of Galinsoga parviflora growing in the selenium-rich ore area of Enshi, Hubei Province, China. This strain could grow at pH 5.0–10.0 and 4–42 °C, with optimal growth at pH 7.0 and 28 °C. It resisted NaCl up to 5% (w/v), with an optimal growth condition of 0.5–1.0%. It tolerated up to 5,000 mg/L of Se4+. The major fatty acids of strain ES5-4T were anteiso-C15:0 (46.5%) and C16:0 (21.7%). The predominant respiratory quinone was MK-7. The polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and an unidentified phospholipid (PL). The 16S rRNA gene sequence implied that ES5-4T belonged to a member of the genus Paenibacillus, with a highest sequence similarity of 98.4% to Paenibacillus pabuli NBRC 13638T. The bac120 tree also verified that the strain was within the genus Paenibacillus. The average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between ES5-4T and closely related members of the genus Paenibacillus were all below the cutoff levels of 95%–96% and 70%, respectively. Therefore, based on phenotypic, chemotaxonomic, and phylogenetic analyses, strain ES5-4T represents a novel Paenibacillus species, for which the name Paenibacillus hubeiensis sp. nov. is proposed. This type strain is ES5-4T (= GDMCC 1.3540T = KCTC 43478T).