Key message A survey of the Eucalyptus grandis genome revealed the presence of 54 laccase genes. Their tissue-specific and stress-induced expression patterns suggest a role in lignification and adaptation to abiotic stresses. Abstract Laccases are multicopper oxidases that play important roles in the oxidation of monolignols during lignin biosynthesis and are reported to be functionally involved in plant development and stress responses. In this study, a genome-wide survey of the Eucalyptus grandis genome revealed the presence of 54 putative LAC genes (referred as EgrLAC), which were assigned to six different phylogenetic groups. Among them, 17 were predicted to be potential targets of miR397, a negative regulator of lignin biosynthesis. Based on different RNA-Seq datasets, distinct organ/tissue expression patterns of the identified EgrLAC genes were ascertained. The vast majority, however, showed enriched expression in the vascular tissues of roots and stems. Additional expression profiling of selected EgrLAC genes revealed differential expression in response to oxidative and osmotic stresses, suggesting a role in abiotic stress responses. Parallel promoter analysis of EgrLAC4, a close homologue to the Arabidopsis lignin biosynthesis-related gene AtLAC17, revealed a vascular expression pattern, mostly associated with the phloem. Overall, our data point to an involvement of the identified EgrLAC genes in lignification and in Eucalyptus adaptation to abiotic stresses.

About 95% of Eucalyptus species present an organ known as a lignotuber, a basal woody swelling that holds a large number of dormant buds in a protected position along with carbohydrates and other nutrients. The importance of this trait in Eucalyptus species relates to its regenerative capacity, particularly in the context of coppicing practices and survival in regions of high abiotic stress, especially fire. In this study, we identified and characterized a genomic region associated with the lignotuber trait in commercially important Eucalyptus species by developing a polymorphic marker that co-segregates with lignotuber presence. The marker was then converted into a SCAR (Sequence Characterized Amplified Region) marker, validated in four other Eucalyptus species and hybrids and analyzed in silico. Our investigation presents a marker (ELig) that is effective in identifying individuals with lignotuber. In silico and Southern blot analyses show that the marker is present in a single copy region and is related to auxilin/cyclin-G associated kinase, containing a DnaJ domain. The ELig marker is an important tool that can be used to manage crosses in Eucalyptus breeding programs and inform studies involving lignotuber development and genetics. Eucalyptus is a widely planted tree genus due to its ability to adapt, grow, and produce quality wood that can be used for multiple end purposes 1,2. In Brazil, Eucalyptus plantations are extremely important as they comprise more than 71% of the total forest plantation area (5.56 million ha), making the country a leader in the forestry sector 3. In this context, researchers and foresters seek to implement tree improvement programs, advance silvicultural practices to increase productivity, introduce desirable traits, and reduce the environmental impacts of eucalypt plantations 4-6. A common practice in Eucalyptus management is coppicing, which offers an initial sprout growth rate greater than planting seedlings and is enhanced by the presence of an organ known as a lignotuber 7-9. Natural conditions in Australia led to the evolution of the Eucalyptus genus which is strongly associated with the occurrence of fire. Trees have been both survivors and promoters of fire over millions of years, leading to the development of a series of regeneration strategies including lignotubers 10. Lignotubers are basal, woody swellings that can form rapidly during the seedling stage 11-13. They hold a large number of dormant buds in a protected position, along with carbohydrates and nutrients necessary for bud development 11,12,14. Under normal conditions, the buds remain dormant, but they can be activated by stress factors, such as defoliation 14 , fire and coppicing 9,15 , and nutrient and water deficiencies 13,16 , underscoring the importance of the lignotuber for tree survival. These organs are present in 95% of all Eucalyptus species, including E. urophylla, E. brassiana, and E. saligna; however, some commercial species, such as E. grandis, E. regnans, E. delegatensis, E. pilularis, and E. niten...