Bing He

During the process of flue-curing and processing, leaves from cash crops such as tea and tobacco frequently undergo a phenomenon of browning, leading to reduced quality and significant economic losses. Despite a variety of approaches developed to suppress browning, little is known about the role that flue-curing of postharvest leaves with stems plays in delaying browning. This study investigated the impact of leaf-with-stem (LWS) flue-curing on the browning of tobacco and its underlying mechanisms. Physiological results indicated that LWS flue-curing effectively delayed browning by enhancing antioxidant capacity and maintaining reactive oxygen species (ROS) levels during the yellowing stage. Comprehensive transcriptome and metabolome analyses showed that LWS flue-curing significantly influenced various metabolic pathways. Specifically, 196, 218, and 402 metabolites, and 65, 131, and 718 genes exhibited significant changes at the 38 °C, 40 °C, and 42 °C stages, respectively, inhibiting membrane lipid degradation and enhancing the supply of reducing hydrogen through the oxidative pentose-phosphate pathway. Additionally, hormone signaling pathways were found to be associated with LWS flue-curing. These findings highlight the complex interplay of metabolic pathways and signaling networks in attenuating browning, providing valuable insights for minimizing postharvest leaf browning during flue-curing and processing.

Enzymatic browning reactions, triggered by oxidative stress, significantly compromise the quality of harvested crops during postharvest handling. This has profound implications for the agricultural industry. Recent advances have employed a systematic, multi-omics approach to developing anti-browning treatments, thereby enhancing our understanding of the resistance mechanisms in harvested crops. This review illuminates the current multi-omics strategies, including transcriptomic, proteomic, and metabolomic methods, to elucidate the molecular mechanisms underlying browning. These strategies are pivotal for identifying potential metabolic markers or pathways that could mitigate browning in postharvest systems.

Flue-curing of top leaves with stems is a widely applied curing technology. Owing to the presence of stems, the quality of flue-cured leaves was significantly improved. However, the contribution of stems to flue-cured leaves is still unknown. In this study, the differences in physicochemical properties and metabolomics data between separated leaves (stem(-)) and leaves with stems (stem(+)) were investigated. The metabolic profiling of stem(+) was significantly different from that of stem(-), with phytohormone indole-3-acetic acid (IAA) being one of the most differential metabolites. The presence of stems reduced the rate of water loss in leaves, which led to less ROS accumulation, higher antioxidant enzyme activities and a lower level of membrane lipid peroxidation in stem(+) than in stem(-). The presence of stems also helped maintain the cellular membrane integrity of leaf cells by preventing the accumulation of IAA in leaf cells. Better cellular membrane integrity during flue-curing means a lower risk of leaf browning. In addition, stem(+) had a lower starch content than stem(-) because of a higher level of amylase activity. In summary, these results indicated that the presence of stems caused metabolism changes in leaves, prevented flue-cured leaves from browning and enhanced starch degradation in leaves during flue-curing.

Plants have evolved complex mechanisms to respond to the fluctuation of available nitrogen (N) in soil, but the genetic mechanisms underlying the N response in crops are not well-documented. In this study, we generated a time series of NO₃⁻-mediated transcriptional profiles in roots of maize and sorghum, respectively. Using weighted gene co-expression network analysis, we identified modules of co-expressed genes that related to NO₃⁻ treatments. A cross-species comparison revealed 22 conserved modules, of which four were related to hormone signaling, suggesting that hormones participate in the early nitrate response. Three other modules are composed of genes that are mainly upregulated by NO₃⁻ and involved in nitrogen and carbohydrate metabolism, including NRT, NIR, NIA, FNR, and G6PD2. Two G2-like transcription factors (ZmNIGT1 and SbNIGT1), induced by NO₃⁻ stimulation, were identified as hub transcription factors (TFs) in the modules. Transient assays demonstrated that ZmNIGT1 and SbNIGT1 are transcriptional repressors. We identified the target genes of ZmNIGT1 by DNA affinity-purification sequencing (DAP-Seq) and found that they were significantly enriched in catalytic activity, including carbon, nitrogen, and other nutrient metabolism. A set of ZmNIGT1 targets encode transcription factors (ERF, ARF, and AGL) that are involved in hormone signaling and root development. We propose that ZmNIGT1 and SbNIGT1 are negative regulators of nitrate responses that play an important role in optimizing nutrition metabolism and root morphogenesis. Together with conserved N responsive modules, our study indicated that, to encounter N variation in soil, maize and sorghum have evolved an NO₃⁻-regulatory network containing a set of conserved modules and transcription factors.

Microalgae possess higher photosynthetic efficiency and accumulate more neutral lipids when supplied with high-dose CO₂. However, the nature of lipid accumulation under conditions of elevated CO₂ has not been fully elucidated so far. We now revealed that the enhanced lipid accumulation of Chlorella in high-dose CO₂ was as efficient as under heterotrophic conditions and this may be attributed to the driving of enlarged carbon source. Both photoautotrophic and heterotrophic cultures were established by using Chlorella sorokiniana CS-1. A series of changes in the carbon fixation, lipid accumulation, energy conversion, and carbon-lipid conversion under high-dose CO₂ (1–10 %) treatment were characterized subsequently. The daily carbon fixation rate of C. sorokiniana LS-2 in 10 % CO₂ aeration was significantly increased compared with air CO₂. Correspondingly, double oil content (28 %) was observed in 10 % CO₂ aeration, close to 32.3 % produced under heterotrophic conditions. In addition, with 10 % CO₂ aeration, the overall energy yield (Ψ) in Chlorella reached 12.4 from 7.3 % (with air aeration) because of the enhanced daily carbon fixation rates. This treatment also improved the energetic lipid yield (Y_lipid/Es) with 4.7-fold, tending to the heterotrophic parameters. More significantly, 2.2 times of carbon-lipid conversion efficiency (η_{Clipid/Ctotal}, 42.4 %) was observed in 10 % CO₂ aeration, towards to 53.7 % in heterotrophic cultures, suggesting that more fixed carbon might flow into lipid synthesis under both 10 % CO₂ aeration and heterotrophic conditions. Taken together, all our evidence showed that 10 % CO₂ may push photoautotrophic Chlorella to display heterotrophic-like efficiency at least in lipid production. It might bring us an efficient model of lipid production based on microalgal cells with high-dose CO₂, which is essential to sustain biodiesel production at large scales.