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.

Macadamia is a kind of evergreen nut trees which belong to the Proteaceae family. The two commercial macadamia species, Macadamia integrifolia and M. tetraphylla , are highly prized for their edible kernels. Catherine et al. reported M. integrifolia genome using NGS sequencing technology. However, the lack of a high-quality assembly for M. tetraphylla hinders the progress in biological research and breeding program. In this study, we report a high-quality genome sequence of M. tetraphylla using the Oxford Nanopore Technologies (ONT) technology. We generated an assembly of 750.54 Mb with a contig N50 length of 1.18 Mb, which is close to the size estimated by flow cytometry and k-mer analysis. Repetitive sequence represent 58.57% of the genome sequence, which is strikingly higher compared with M. integrifolia . A total of 31,571 protein-coding genes were annotated with an average length of 6,055 bp, of which 92.59% were functionally annotated. The genome sequence of M. tetraphylla will provide novel insights into the breeding of novel strains and genetic improvement of agronomic traits.

Rubber tree (Hevea brasiliensis) is a crucial economic crop in tropical regions worldwide; however, low temperature in some areas have become a major source of abiotic stress that constrains the sustainable development of the natural rubber industry. Superoxide dismutase (SOD) is an enzyme that catalyzes the dismutation of the superoxide anion radical (O₂•⁻) into oxygen (O₂) and hydrogen peroxide (H₂O₂). Thus, SOD is an important antioxidant defense under plant stress defense, and also may help to improve rubber tree protection from the cold. In this study, a Cu/Zn superoxide dismutase gene, HbCSD2, was successfully cloned from the rubber tree via PCR amplification. Subcellular localization analysis revealed that HbCSD2 is localized in the cytoplasm and nucleus. Under low-temperature stress, the seed germination rate, fresh weight, and survival rate of HbCSD2-overexpressing transgenic Arabidopsis were significantly higher than those of the wild-type (WT) plants. Conversely, the malformed seedling rate was considerably lower. Compared to WT plants, the transgenic Arabidopsis showed marked increases in SOD, catalase (CAT), and peroxidase (POD) activity, as well as the soluble sugar content. Meanwhile, the levels of malondialdehyde (MDA), H₂O₂, and O₂•⁻ were significantly lower. This study confirms that HbCSD2 enhances cold tolerance by boosting antioxidant enzyme activity and ROS scavenging capabilities, while reducing membrane lipid peroxidation. These findings offer valuable insights into the regulatory role of HbCSD2 and the mechanisms behind stress responses in the rubber tree.