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.

Mitochondrial Uncoupling Proteins (UCPs) are mitochondrial inner membrane proteins that dissipate the proton electrochemical gradient generated by the respiratory chain complexes. In plants, these proteins are crucial for maintaining mitochondrial reactive oxygen species (ROS) homeostasis. In this study, single T-DNA insertion mutants for two (AtUCP1and AtUCP2) out of the three UCP genes present in Arabidopsis thaliana were employed to elucidate their potential roles in planta. Our data revealed a significant increase in the ATP/ADP ratios of both mutants, indicating clear alterations in energy metabolism, and a reduced respiratory rate in atucp2. Phenotypic characterization revealed that atucp1 and atucp2 plants displayed reduced primary root growth under normal and stressed conditions. Moreover, a reduced fertility phenotype was observed in both mutants, which exhibited increased number of sterile siliques and lower seed yield compared with wild-type plants. Reciprocal crosses demonstrated that both male and female fertility were compromised in atucp1, while such effect was exclusively observed in the male counterpart in atucp2. Most strikingly, a pronounced accumulation of hydrogen peroxide in the reproductive organs was observed in all mutant lines, indicating a disturbance in ROS homeostasis of mutant flowers. In line, the atucp1 and atucp2 mutants exhibited higher levels of ROS in pollen grains. Also in support, alternative oxidase 1a was highly induced in mutant flowers, while the expression profiles of transcription factors implicated in gene regulation during female and male reproductive organ/tissue development were perturbed. Overall, these data give support for an important role for AtUCP1 and AtUCP2 in flower oxidative homeostasis and overall plant fertility.

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