The rubber tree is the primary source of natural rubber and is mainly cultivated in Southeast Asian countries. Low temperature is the major abiotic stress affecting the yield of the rubber tree. Therefore, uncovering the cold resistance mechanism in the rubber tree is necessary. The present study used RNA-sequencing technology and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to analyze the transcriptomic and metabolomic changes in two rubber tree clones with different cold resistance capacities (temperature-sensitive Reyan 8-79 and cold-resistant Yunyan 77-4) at 0 h, 2 h, 6 h, and 20 h of exposure to 4°C. Independent analysis of the transcriptome and metabolitome showed that under prolonged low-temperature treatment, Yunyan 77-4 expressed more genes involved in regulating enzyme activity, changing cell permeability, and synthesizing significant metabolites, such as flavonoids and amino acids, than Reyan 8-79. The KEGG annotation and enrichment analysis identified arginine metabolism and biosynthesis of flavonoids as the major pathway associated with cold resistance. Integrated transcriptome and metabolome analysis showed that the increase in the expression of genes modulated flavonoid biosynthesis, arginine biosynthesis, and anthocyanins biosynthesis, resulting in higher levels of metabolites, such as naringenin chalcone, apigenin, dihydroquercetin, cyanidin 3-glucoside, L-arginosuccinate, N-acetyl-ornithine, ornithine, and N-acetyl-glutamate, in Yunyan 77-4 than in Reyan 8-79 after prolonged low-temperature treatment. Phylogenetic analysis identified the genes, such as CHS (gene356) and F3H (gene33147) of flavonoid biosynthesis and NAGS (gene16028, gene33765), ArgC (gene2487), and ASS (gene6161) of arginine biosynthesis were the key genes involved in the cold resistant of rubber tree. Thus, the present study provides novel insights into how rubber clones resist cold and is a valuable reference for cold-resistance breeding.

A new species of Lysimachia, L. xiangxiensis (Primulaceae), is described and illustrated from western Hunan, central China. The species is similar to L. melampyroides in plant densely strigillose, leaves subglabrous adaxially, and flowers usually solitary in axils of upper leaves, but differs by the succulent leaves, the creeping or ascending stems 15–25 cm long, and the suborbicular to broadly elliptic corolla lobes. This new species is also supported by a molecular phylogenetic analysis of some Lysimachia species based on ITS sequence data.

Catalase (CAT) is one of the key enzymes involved in antioxidant defense systems and mainly scavenges H₂O₂ and plays a vital role in plant growth, development, and various adverse stresses. To date, a systematic study of the CAT gene family in rubber tree has not been reported. In this study, five HbCAT gene family members were identified from the rubber tree genome, and these were mainly clustered into two subfamilies. Gene structure and motif analysis showed that exon-intron and motif patterns were conserved across different plant species. Sequence analysis revealed that HbCAT proteins contain one active catalytic site, one heme-ligand signature sequence, three conserved amino acid residues (His, Tyr, and Asn), and one peroxisome-targeting signal 1 (PTS1) sequence. Fragment duplication is a selection pressure for the evolution of the HbCAT family based on Ka/Ks values. Analysis of cis-acting elements in the promoters indicated that HbCAT gene expression might be regulated by abscisic acid (ABA), salicylic acid (SA), and MYB transcription factors; furthermore, these genes might be involved in plant growth, development, and abiotic stress responses. A tissue-specific expression analysis showed that HbCATs gradually increased with leaf development and were highly expressed in mature leaves. Gene expression profiling exhibited the differential expression of the HbCATs under cold, heat, drought, and NaCl stresses. Our results provide comprehensive information about the HbCAT gene family, laying the foundation for further research on its function in rubber tree.

Horsfieldia pandurifolia is a member of Myristicaceae. The H. pandurifolia chloroplast genome is found to be 155,695 bp in length and has a base composition of A (30.01%), G (19.31%), C (19.90%), and T (30.78%). The genome contained two short inverted repeats (IRa and IRb) regions (48,062 bp) which were separated by a large single copy (LSC) region (92,561 bp) and a small single copy (SSC) region (15,072 bp). The genome encodes 121 unique genes, including 86 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of H. pandurifolia was aligned together with five other species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of H. pandurifolia.

Myristica yunnanensis is a member of Myristicaceae. The M. yunnanensis chloroplast genome is found to be 155,923 bp in length and has a base composition of A (30.04%), G (19.28%), C (19.91%), and T (30.77%). The genome contained two short inverted repeat (IRa and IRb) regions (48,004 bp) which were separated by a large single-copy (LSC) region (87,088 bp) and a small single-copy (SSC) region (20,731 bp). The genome encodes 120 unique genes, including 85 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of M. yunnanensis was aligned together with Horsfieldia pandurifolia and other Magnoliales and basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of M. yunnanensis.

Horsfieldia amygdalina is a member of Myristicaceae. The H. amygdalina chloroplast genome is found to be 155,683 bp in length and has a base composition of A (29.99%), G (19.32%), C (19.92%), and T (30.77%). The genome contained two short inverted repeat (IRa and IRb) regions (37,754 bp) which were separated by a large single copy (LSC) region (86,931 bp) and a small single copy (SSC) region (30,998 bp). The genome encodes 121 unique genes, including 86 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of H. amygdalina was aligned together with Horsfieldia pandurifolia, Myristica yunnanensis and other Magnoliales and basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of H. amygdalina.