Plants have evolved complex terpene defenses. Terpenoids accumulate in plant tissues or release as volatile in response to ever-changing environment, playing essential roles in chemo-ecological functions as defense against pathogen and insect, improving pollination and seed dispersal, facilitation plant-to-plant communication. They are also gaining attention in pharmaceuticals, nutraceuticals, fragrance, and biofuels. Here, we highlight the recent progress in the fundamental pathways of terpenoid biosynthesis, key enzymes, and their corresponding genes involved in terpenoid synthesis. We identified the further exploration of biosynthetic networks and the development of novel terpenoid resources, proposed the need for further exploration of biosynthetic networks and the development of novel terpenoid resources. Based on that knowledge, future research should be directed towards the mechanisms governing terpenoid biosynthesis dependent environmental change and molecular breeding.

AREB/ABF/ABI5 (ABA-responsive element-binding protein/ABRE binding factors and ABA INSENSITIVE 5) transcription factors are involved in regulating the expression of ABA (abscisic acid)-related genes and improving plant adaptability to environmental stress. To explore the influence of AREB/ABF transcription factors on santalol synthesis, we conducted a genome-wide analysis of the AREB gene family in sandalwood, identified 10 SaAREB genes, and divided them into five subfamilies. We found that all SaAREB genes encoded unstable hydrophilic proteins and the subcellular localization prediction of SaAREBs was that they are located in the nucleus. AREB/ABF genes belong to the bZIP-A subfamily and we found that the 10 AREB proteins all contained bZIP (basic region leucine zipper) and four potential phosphorylation sites (RXXS/T). According to the collinearity analysis results, four of the SaAREB genes were involved in two fragment duplication events. Through qRT-PCR (real-time fluorescence quantitative PCR), we explored the expression profile of SaAREB in different tissues; the effects of ABA treatment and drought treatment on AREB transcription factors were predicted. From the expression of different tissues, we found that SaAREB1 not only responded to prolonged drought but also was highly expressed in stems. Moreover, SaAREB3, SaAREB7, and SaAREB8 specifically respond to ABA treatment. Based on RNA-seq (RNA sequencing) data, we found that SaAREB6 and SaAREB8 were highly expressed in the sapwood and transition regions. Regarding SaCYP736A167, as a key gene in santalol synthesis, its promoter contains the most ABRE cis-reactive elements. These results provide a basis for further analysis of the role of the Santalum album L. (S. album) ABRE/ABF/ABI5 genes in the formation of santalols.

Sandalwood (Santalum album), a culturally significant and economically valuable horticultural species, is renowned for its heartwood and essential oils enriched with sesquiterpene compounds such as santalol. Despite progress in elucidating the biosynthetic pathway of these valuable metabolites, the transcriptional regulation of this process, particularly under abiotic stress conditions, remains largely unexplored. Under drought conditions, we observed a marked increase in SaAREB6 expression, paralleled by elevated levels of santalols. Moreover, we identified SaCYP736A167, a cytochrome P450 mono-oxygenase gene, as a direct target of SaAREB6. Using electrophoretic mobility shift assays (EMSAs), microscale thermophoresis assays (MSTs), and dual luciferase assays (DLAs), we validated the precise and specific interaction of SaAREB6 with the promoter region of SaCYP736A167. This interaction leads to the upregulation of SaCYP736A167, which in turn catalyzes the final steps in the conversion of sesquiterpene precursors to santalols, thereby reinforcing the connection between SaAREB6 activity and increased santalol production during drought. Collectively, our work illuminates the previously uncharacterized role of SaAREB6 in orchestrating a transcriptional regulation that facilitates drought-induced santalol biosynthesis in sandalwood, presenting opportunities for genetic engineering strategies to improve heartwood and essential oil yields in this economically vital species.

Heartwood, serving as the central constituent of the xylem, plays a crucial role in the growth, development, and resilience of trees. The process of heartwood formation constitutes a complex biological phenomenon influenced by various factors. A thorough examination of the mechanisms underpinning heartwood formation not only enhances our understanding of the growth and developmental paradigms regulating trees but also provides essential theoretical support and practical insights for the timber industry, forestry management, and ecological conservation. This paper offers an overview of the foundational processes involved in heartwood formation in plants. Furthermore, it presents a comprehensive review of the latest research advancements in this domain, covering five key aspects: metabolism, hormonal regulation, transcriptional regulation, cell biology, and environmental influences. This review serves as a valuable basis for future research endeavors in related academic fields.

Interest in improving plant nitrogen use efficiency (NUE) in conjunction with reduced usage of nitrogen (N) fertilizers in forestry management is growing. Although biochar amendment is widely applied to increase soil nutrient availability and NUE, the mechanism underlying their positive effects remains little understood. We treated the economically important eucalypt species with biochar (BC), N-enriched fertilizer with ¹⁵N isotope labeling (NF), and biochar plus ¹⁵N-labeled fertilizer (NFB). Moreover, we determined plant N absorption and soil N availability, soil bacterial community composition and its putative keystone taxa, and plant NUE and competition index under different treatments. Our results indicated that NF and NFB significantly increased plant atom % ¹⁵N in both eucalypt stem, root, and foliar, as well as the competition index of eucalypt to forbs for acquiring N. NF and BC increased the network complexity of keystone taxa by shifting putative keystone taxa, including phylum Proteobacteria, Chloroflexi, Actinobacteria, Acidobacteria, and Firmicutes. Piecewise structural equation modeling indicated that variations in plant performance were best directly and positively predicted by soil Proteobacteria. This study highlights the importance of interactive effects between biochar and N fertilizer on plant performance mediated by soil microbial community. The change in soil putative keystone taxa has the potential to be a suitable predictor for plant performance in terms of biochar. Our findings may provide important implications for improving fertilization and afforestation management.