The WUSCHEL-related homeobox (WOX) gene family are key players in the rooting process. Eucalyptus is an important plant species of artificial forests in China. It is mainly grown through tissue culture of many excellent clonal materials, in which rooting is a key step. In the present study, by using the genome data of Eucalyptus grandis, Corymbia citriodora, E. pellita, and E. urophylla × E. grandis, the members of the eucalyptus WOX gene family were identified and analyzed by bioinformatics techniques. The eucalyptus WOX gene family members are unstable proteins, with 7 acidic proteins and 24 basic proteins, and no signal peptide region was detected. Subcellular localization prediction indicated that all these proteins are localized in the nucleus. Motif analysis showed that eucalyptus WOX genes share the same motifs. Phylogenetic tree and gene expression analyses revealed that the eucalyptus WOX genes are highly conserved during the evolution process. Moreover, the WOX protein sequences are also highly conserved within the species, with higher similarity between woody plants. The EupWOX gene showed tissue-specific expression, with EupWOX1 and EupWOX11 specifically expressed in the roots of E. urophylla × E. pellita clonal tissue culture during the late-stage rooting. This finding suggests that EupWOX1 may be a key regulatory gene induced by the root primordium and is critically related to the rooting rate. EupWOX1, EupWOX5, and EupWOX13 could be the key regulatory genes for adventitious root formation. EupWOX1, EupWOX5, and EupWOX13 could be the key regulatory genes for the elongation of adventitious roots and the growth of adventitious lateral roots. EupWOX5 and EupWOX13 could play a critical role, not only in the formation of adventitious roots and adventitious lateral roots of E. urophylla clonal tissue culture but also in the root elongation process. These results will help us understand the complexity of rooting in different lines and provide valuable information for future functional characterization of specific genes in eucalyptus clones.

Selecting high-quality varieties with disease resistance by artificial crossbreeding is the most fundamental way to address the damage caused by Calonectria spp. in eucalypt plantations. However, understanding the mechanism of disease-resistant heterosis occurrence in eucalypts is crucial for successful crossbreeding. Two eucalypt hybrids, the susceptible EC333 (H1522 × unknown) and the resistant EC338 (W1767 × P9060), were screened through infection with Calonectria isolates, a pathogen that causes eucalypt leaf blight. RNA-Seq was performed on the susceptible hybrid, the disease-resistant hybrid, and their parents. The gene differential expression analysis showed that there were 3912 differentially expressed genes between EC333 and EC338, with 1631 up-regulated and 2281 down-regulated genes. The expression trends of the differential gene sets in P9060 and EC338 were similar. However, the expression trend of W1767 was opposite that of EC338. The similarity of the expression and the advantage of stress resistance in E. pellita suggested that genes with significant differences in expression likely relate to disease resistance. A GSEA based on GO annotations revealed that the carbohydrate binding pathway genes were differentially expressed between EC338 and EC333. The gene pathways that were differentially expressed between EC338 and EC333 revealed by the GSEA based on KEGG annotations were the sesquiterpenoid and triterpenoid biosynthesis pathways. The alternative splicing analysis demonstrated that an AS event between EC338 and EC333 occurred in LOC104426602. According to our SNP analysis, EC338 had 626 more high-impact mutation loci than the male parent P9060 and 396 more than the female parent W1767; W1767 had 259 more mutation loci in the downstream region than EC338, while P9060 had 3107 fewer mutation loci in the downstream region than EC338. Additionally, EC338 had 9631 more mutation loci in the exon region than EC333. Modules were found via WGCNA that were strongly and oppositely correlated with EC338 and EC333, such as module MEsaddlebrown, likely associated with leaf blight resistance. The present study provides a detailed explanation of the genetic basis of eucalypt leaf blight resistance, providing the foundation for exploring genes related to this phenomenon.

Introduction: Wood formation is a crucial developmental stage in the life cycle of a woody plant; this process has substantial scientific research implications and practical applications. However, the mechanisms underlying woody plant development, especially the process of wood formation, remain poorly understood. As eucalyptus is one of the fastest growing tree species in the world, understanding the mechanism of wood formation in eucalyptus will greatly promote the development of molecular breeding technology for forest trees.Results: In this study, we investigated the proteomic profile of immature xylem at four different ages of Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) using iTARQ technology. We identified 5236 proteins and 492 differentially abundant proteins (DAPs). The expression profiles of the DAPs corresponding to coding genes associated with wood formation were assessed using qRT-PCR. From the different expression profiles, it is inferred that the genes encoding kinesin, CDKD3, EXPA13, EXPA2, XTH27, EGases, UGT76E2, LAC, CCoAMT, CesA3, PAL, and CAD may undergo posttranscriptional regulation (PTR). Additionally, the genes encoding EIN2, ETR, MC4-like, and XCP may undergo posttranslational modifications (PTMs).Conclusions: We investigated changes in wood formation-related proteins at the protein abundance level in the immature xylem of E. urograndis, thereby elucidating potential regulatory mechanisms of key proteins involved in eucalyptus wood formation. This study may provide theoretical guidance for further research on molecular breeding techniques and genetic improvement related to the cultivation of rapidly growing and high-quality trees.

Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) is a globally significant forest tree species renowned for its rapid growth, high yield, and exceptional wood production efficiency. A comparative analysis of its parental genomes, coupled with an in-depth investigation of the expression patterns of wood-related genes, will provide critical genomic resources to enhance research and utilization of this superior eucalypt hybrid species. In this study, we present a draft genome assembly consisting of 592.09 Mb of data, with 99.91% anchored to 11 pseudochromosomes. The assembly achieved a contig N50 of up to 3.73 Mb and a scaffold N50 of up to 58.62 Mb. Gene annotation and evaluation revealed that the E. urograndis genome contains 32,151 genes, of which 93.50% were fully annotated using Benchmarking Universal Single-Copy Orthologs (BUSCOs). Based on evolutionary analysis, E. grandis and E. urograndis are estimated to have diverged approximately 2.90 million years ago (Mya). Additionally, 131 gene families were found to be significantly expanded, and 475 positively selected genes (PSGs) were identified in the E. urograndis genome. Furthermore, RNA sequencing (RNA-seq) technology was employed to analyze allele-specific expression patterns of key enzymes involved in cellulose, xylan, and lignin biosynthesis. Several allele-specific expression genes (ASEGs) were identified, potentially associated with heterosis in E. urograndis. The chromosomal-level genome assembly of E. urograndis presented in this study serves as a valuable genomic resource for eucalyptus molecular breeding, provides novel insights into its evolution, wood formation improvement, and adaptability, and enhances our understanding of genetic and molecular mechanisms underlying heterosis in Eucalyptus hybrids.

(1) Selecting high-quality varieties with disease resistance by crossbreeding artificially is the most fundamental way to address the damage caused by Calonectria spp in eucalypt plantations. However, understanding the mechanism of the formation of disease-resistant heterosis in eucalypt is crucial for the success of crossbreeding. (2) Two eucalypt hybrids, susceptible EC333 (H1522 × unknown) and resistant EC338 (W1667 × P9060) were screened in our previous study on the infection of the isolates of Calonectria., which causes eucalypt leaf blight. RNA-Seq sequencing was performed on susceptible hybrid EC333, disease-resistant hybrid EC338 (W1667 × P9060), and their parents. A comparison was conducted between the the transcriptomic data sequenced and the reference genome of Eucalyptus grandis, and the The differential expression of genes and functional annotations between hybrids and parents was identified. (3) Gene differential expression analysis shows that there are 3912 differentially expressed genes between EC333 and EC338, with 1631 up-regulated and 2281 down-regulated. The expression trends of differential gene sets in P9060 and EC338 were similar. However, the expression trend of W1767 was opposite that of EC338. The similarity of expression levels and the advantage of stress resistance of E. pellita suggested that genes with significant differences in expression are likely to be related to disease resistance. The GSEA enrichment based on GO annotation revealed that the carbohydrate binding pathway (GO:0030246) is differentially expressed between EC338 and EC333. The gene pathway that differentially expressed between EC338 and EC333, was revealed by GSEA enrichment based on KEGG annotation, is Sesquiterpenoid and Triterpenoid biosynthesis (EGR00909). The Alternative Splicing analysis demonstrated that the AS events gene between EC338 and EC333 is LOC104426602. According to SNP analysis, EC338 has 626 more high-impact mutation loci than the male parent P9060, and 396 more than the female parent W1767, the maternal parent W1767 has 259 more mutation loci in the downstream region than EC338, while the male parent P9060 has 3107 fewer mutation loci in the downstream region than EC338. Additionally, EC338 has 9631 more mutation loci in the exon region than EC333. These findings suggested that the genetic pathways, specific gene regions, and their quantities might play crucial roles in the formation of heterosis linked to the resistance against eucalypt leaf blight. The modules were found in WGCNA, which were strongly and oppositely correlated with EC338 and EC333, such as module MEsaddlebrown is likely to be associated with leaf blight resistance. (4) The present study provides a detailed explanation of the genetic basis for the heterosis of resistance to eucalypt leaf blight, providing a basis for exploring genes related to resistance to eucalypt leaf blight.