Jingyang Li

Banana cultivars (Musa ssp.) are diploid, triploid and tetraploid hybrids derived from Musa acuminata and Musa balbisiana. We presented a high-quality draft genome assembly of M. balbisiana with 430 Mb (87%) assembled into 11 chromosomes. We identified that the recent divergence of M. acuminata (A-genome) and M. balbisiana (B-genome) occurred after lineage-specific whole-genome duplication, and that the B-genome may be more sensitive to the fractionation process compared to the A-genome. Homoeologous exchanges occurred frequently between A- and B-subgenomes in allopolyploids. Genomic variation within progenitors resulted in functional divergence of subgenomes. Global homoeologue expression dominance occurred between subgenomes of the allotriploid. Gene families related to ethylene biosynthesis and starch metabolism exhibited significant expansion at the pathway level and wide homoeologue expression dominance in the B-subgenome of the allotriploid. The independent origin of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) homoeologue gene pairs and tandem duplication-driven expansion of ACO genes in the B-subgenome contributed to rapid and major ethylene production post-harvest in allotriploid banana fruits. The findings of this study provide greater context for understanding fruit biology, and aid the development of tools for breeding optimal banana cultivars.

Biomass recalcitrance and plant lodging are two complex traits that tightly associate with plant cell wall structure and features. Although genetic modification of plant cell walls can potentially reduce recalcitrance for enhancing biomass saccharification, it remains a challenge to maintain a normal growth with enhanced biomass yield and lodging resistance in transgenic plants. Sucrose synthase (SUS) is a key enzyme to regulate carbon partitioning by providing UDP-glucose as substrate for cellulose and other polysaccharide biosynthesis. Although SUS transgenic plants have reportedly exhibited improvement on the cellulose and starch based traits, little is yet reported about SUS impacts on both biomass saccharification and lodging resistance. In this study, we selected the transgenic rice plants that expressed OsSUS3 genes when driven by the AtCesA8 promoter specific for promoting secondary cell wall cellulose synthesis in Arabidopsis. We examined biomass saccharification and lodging resistance in the transgenic plants and detected their cell wall structures and wall polymer features. During two-year field experiments, the selected AtCesA8::SUS3 transgenic plants maintained a normal growth with slightly increased biomass yields. The four independent transgenic lines exhibited much higher biomass enzymatic saccharification and bioethanol production under chemical pretreatments at P < 0.01 levels, compared with the controls of rice cultivar and empty vector transgenic line. Notably, all transgenic lines showed a consistently enhanced lodging resistance with the increasing extension and pushing forces. Correlation analysis suggested that the reduced cellulose crystallinity was a major factor for largely enhanced biomass saccharification and lodging resistance in transgenic rice plants. In addition, the cell wall thickenings with the increased cellulose and hemicelluloses levels should also contribute to plant lodging resistance. Hence, this study has proposed a mechanistic model that shows how OsSUS3 regulates cellulose and hemicelluloses biosyntheses resulting in reduced cellulose crystallinity and increased wall thickness, thereby leading to large improvements of both biomass saccharification and lodging resistance in transgenic rice plants. This study has demonstrated that the AtCesA8::SUS3 transgenic rice plants exhibited largely improved biomass saccharification and lodging resistance by reducing cellulose crystallinity and increasing cell wall thickness. It also suggests a powerful genetic approach for cell wall modification in bioenergy crops.

The rapid development of automotive industry results in a series of increasingly serious problems such as energy consumption and environmental pollution, so that developing the automotive steels with high-strength and low-density is of great significance for energy conservation and emission reduction. Recently, Fe–Mn–C–Al system steel is favored by numerous researchers because of its low density and excellent combination of strength and ductility. However, too much Al addition inevitably triggers various changes of microstructure, deformation mechanism, and mechanical properties. In this paper, the composition design, production process, strengthening and strain hardening mechanism, and microstructure evolution are systematically expounded. The discussion mainly focuses on various strengthening (solid solution strengthening, grain refinement strengthening and precipitation strengthening) and strain hardening mechanisms (phase transformation-induced-plasticity (TRIP), twinning-induced-plasticity (TWIP), microband-induced-plasticity (MBIP), shear-band-induced-plasticity (SIP) and dynamic slip band refinement (DSBR), etc.). Also, the existing problems and future challenges in Fe–Mn–Al–C low-density steels are pointed out via analyzing the service performance (cryogenic performance, impact toughness, fatigue performance, hydrogen embrittlement, wear performance, and tensile properties). Finally, we look forward to the future development direction of Fe–Mn–Al–C low-density steels and provide the valuable ideas.