An extracellular β-N-acetylhexosaminidase of Medicago truncatula hydrolyzes chitooligosaccharides and is involved in arbuscular mycorrhizal symbiosis but not required for nodulation

Establishment of symbiosis between plants and arbuscular mycorrhizal (AM) fungi depends on fungal chitooligosaccharides (COs) and lipo-chitooligosaccharides (LCOs). The latter are also produced by nitrogen-fixing rhizobia to induce nodules on leguminous roots. However, host enzymes regulating structure and levels of these signals remain largely unknown. Here, we analyzed the expression of a β-N-acetylhexosaminidase gene of Medicago truncatula (MtHEXO2) and biochemically characterized the enzyme. Mutant analysis was performed to study the role of MtHEXO2 during symbiosis. We found that expression of MtHEXO2 is associated with AM symbiosis and nodulation. MtHEXO2 expression in the rhizodermis was upregulated in response to applied chitotetraose, chitoheptaose, and LCOs. M. truncatula mutants deficient in symbiotic signaling did not show induction of MtHEXO2. Subcellular localization analysis indicated that MtHEXO2 is an extracellular protein. Biochemical analysis showed that recombinant MtHEXO2 does not cleave LCOs but can degrade COs into N-acetylglucosamine (GlcNAc). Hexo2 mutants exhibited reduced colonization by AM fungi; however, nodulation was not affected in hexo2 mutants. In conclusion, we identified an enzyme, which inactivates COs and promotes the AM symbiosis. We hypothesize that GlcNAc produced by MtHEXO2 may function as a secondary symbiotic signal.

Zebrafish ELL-associated factors Eaf1/2 modulate erythropoiesis via regulating gata1a expression and WNT signaling to facilitate hypoxia tolerance

EAF1 and EAF2, the eleven-nineteen lysine-rich leukemia (ELL)-associated factors which can assemble to the super elongation complex (AFF1/4, AF9/ENL, ELL, and P-TEFb), are reported to participate in RNA polymerase II to actively regulate a variety of biological processes, including leukemia and embryogenesis, but whether and how EAF1/2 function in hematopoietic system related hypoxia tolerance during embryogenesis remains unclear. Here, we unveiled that deletion of EAF1/2 (eaf1^-/- and eaf2^-/-) caused reduction in hypoxia tolerance in zebrafish, leading to reduced erythropoiesis during hematopoietic processes. Meanwhile, eaf1^-/- and eaf2^-/- mutants showed significant reduction in the expression of key transcriptional regulators scl, lmo2, and gata1a in erythropoiesis at both 24 h post fertilization (hpf) and 72 hpf, with gata1a downregulated while scl and lmo2 upregulated at 14 hpf. Mechanistically, eaf1^-/- and eaf2^-/- mutants exhibited significant changes in the expression of epigenetic modified histones, with a significant increase in the binding enrichment of modified histone H3K27me3 in gata1a promoter rather than scl and lmo2 promoters. Additionally, eaf1^-/- and eaf2^-/- mutants exhibited a dynamic expression of canonical WNT/β-catenin signaling during erythropoiesis, with significant reduction in p-β-Catenin level and in the binding enrichment of both scl and lmo2 promoters with the WNT transcriptional factor TCF4 at 24 hpf. These findings demonstrate an important role of Eaf1/2 in erythropoiesis in zebrafish and may have shed some light on regeneration medicine for anemia and related diseases and on molecular basis for fish economic or productive traits, such as growth, disease resistance, hypoxia tolerance, and so on.

Lipid-related metabolism during zebrafish embryogenesis under unbalanced copper homeostasis

Copper (Cu) is an essential trace element, playing an important role in lipid metabolism, and its transporters ATP7A and ATP7B, as Cu-transporting P-type ATPases, are involved in maintaining the Cu homeostasis in cells. Numerous studies in mammals have shown that Cu homeostasis and lipid metabolism are closely related, but studies on the link between the effects of excess Cu, ATP7A, and ATP7B on lipid metabolism during vertebrate embryogenesis are scarce. In this study, zebrafish disease models with Cu overload and ATP7A and ATP7B inactivation, respectively, were used to study the lipid metabolism-related differentially expressed genes (DEGs) which were enriched in the models. The dynamic and spatiotemporal expressions of the DEGs in WTs, atp7a^-/-, and atp7b^-/- mutants with or without Cu stress were unveiled in this study and they mostly distributed in brain at 24 hpf then in liver and intestine at 96 hpf, suggesting their potential roles in lipid and glycogen metabolism to apply energy for normal development in zebrafish. Meanwhile, the correlation analysis for the DEGs among the three groups unveiled that most of the DEGs were involved in the glyceride metabolism pathway. This is the first report to establish the relationship between atp7a and atp7b with Cu-stimulated intestinal and liver lipid metabolism during fish embryogenesis, and this study will provide a theoretical basis for fish embryonic development and lipid metabolism disorders under unbalanced copper homeostasis.

Use of the rhizobial type III effector gene nopP to improve Agrobacterium rhizogenes-mediated transformation of Lotus japonicus

BACKGROUND

Protocols for Agrobacterium rhizogenes-mediated hairy root transformation of the model legume Lotus japonicus have been established previously. However, little efforts were made in the past to quantify and improve the transformation efficiency. Here, we asked whether effectors (nodulation outer proteins) of the nodule bacterium Sinorhizobium sp. NGR234 can promote hairy root transformation of L. japonicus. The co-expressed red fluorescent protein DsRed1 was used for visualization of transformed roots and for estimation of the transformation efficiency.

RESULTS

Strong induction of hairy root formation was observed when A. rhizogenes strain LBA9402 was used for L. japonicus transformation. Expression of the effector gene nopP in L. japonicus roots resulted in a significantly increased transformation efficiency while nopL, nopM, and nopT did not show such an effect. In nopP expressing plants, more than 65% of the formed hairy roots were transgenic as analyzed by red fluorescence emitted by co-transformed DsRed1. A nodulation experiment indicated that nopP expression did not obviously affect the symbiosis between L. japonicus and Mesorhizobium loti.

CONCLUSION

We have established a novel protocol for hairy root transformation of L. japonicus. The use of A. rhizogenes LBA9402 carrying a binary vector containing DsRed1 and nopP allowed efficient formation and identification of transgenic roots.

Re-Evaluation of Phylogenetic Relationships among Species of the Mangrove Genus Avicennia from Indo-West Pacific Based on Multilocus Analyses

Avicennia L. (Avicenniaceae), one of the most diverse mangrove genera, is distributed widely in tropical and subtropical intertidal zones worldwide. Five species of Avicennia in the Indo-West Pacific region have been previously described. However, their phylogenetic relationships were determined based on morphological and allozyme data. To enhance our understanding of evolutionary patterns in the clade, we carried out a molecular phylogenetic study using wide sampling and multiple loci. Our results support two monophyletic clades across all species worldwide in Avicennia: an Atlantic-East Pacific (AEP) lineage and an Indo-West Pacific (IWP) lineage. This split is in line with biogeographic distribution of the clade. Focusing on the IWP branch, we reconstructed a detailed phylogenetic tree based on sequences from 25 nuclear genes. The results identified three distinct subclades, (1) A. rumphiana and A. alba, (2) A. officinalis and A. integra, and (3) the A. marina complex, with high bootstrap support. The results strongly corresponded to two morphological traits in floral structure: stigma position in relation to the anthers and style length. Using Bayesian dating methods we estimated diversification of the IWP lineage was dated to late Miocene (c. 6.0 million years ago) and may have been driven largely by the fluctuating sea levels since that time.