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.

Heat-shock transcription factors (Hsfs) play a pivotal role in the response of plants to various stresses. The present study aimed to characterize the Hsf genes in the rubber tree, a primary global source of natural rubber. In this study, 30 Hsf genes were identified in the rubber tree using genome-wide analysis. They possessed a structurally conserved DNA-binding domain and an oligomerization domain. On the basis of the length of the insert region between HR-A and HR-B in the oligomerization domain, the 30 members were clustered into three classes, Classes A (18), B (10), and C (2). Members within the same class shared highly conserved gene structures and protein motifs. The background expression levels of 11 genes in cold-tolerant rubber-tree clone 93-14 were significantly higher than those in cold-sensitive rubber-tree clone Reken501, while four genes exhibited inverse expression patterns. Upon cold stress, 20 genes were significantly upregulated in 93-114. Of the upregulated genes, HbHsfA2b, HbHsfA3a, and HbHsfA7a were also significantly upregulated in three other cold-tolerant rubber-tree clones at one or more time intervals upon cold stress. Their nuclear localization was verified, and the protein–protein interaction network was predicted. This study provides a basis for dissecting Hsf function in the enhanced cold tolerance of the rubber tree.

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.

Self-incompatibility (SI) significantly reduces crop yield, often far below its genetic potential. Developing self-compatible varieties is the most effective strategy for overcoming SI in crops. Most macadamia ( Macadamia SPP.) species exhibit SI or partial self-incompatibility (PSI), so the efficient identification of self-compatible germplasms has emerged as a crucial topic. To characterize self-incompatibility phenotypes in macadamia germplasm resources, we conducted a four-year field study using the field-bagging method and established a standardized classification system of self-incompatibility. That is, the degree of SI was based on the final self-incompatibility index (F_SI), which was calculated based on the open-pollination final nut set per raceme (OP_FNS) and self-pollination final nut set per raceme (SP_FNS) values (strong SI: F_SI ≥ 0.7, medium SI: 0.4 ≤ F_SI <0.7, and weak SI: F_SI < 0.4). To develop a method for identifying macadamia SI more efficient and cost-effective than the field-bagging method, we employed pollen tube fluorescence staining, where the degree of SI was classified based on the percentage of pistils for which the pollen tube length exceeded 7/10 of the style (PLS) (strong SI: PLS ≤ 16%, medium SI: 16% < PLS ≤ 35%, and weak SI: PLS > 35%). Through comprehensive analysis of the field-bagging and fluorescence-microscopy observations, thirteen varieties with strong SI (816, 778, 842, Special, 812, D, 820, 246, 772, A16, A4, 951, and 695), six varieties with moderate SI (851, 828, 508, 936, O.C, and D4), and four varieties with weak SI (915, HY, 836, and 814) were identified. Our study provides a theoretical foundation and technical support for advancing germplasm resource innovation, and the genetic improvement and breeding of self-compatible macadamia varieties.