论文内容
前言：
气候变化是由大气中的温室气体（如二氧化碳、甲烷）的积累引起的，导致地球上的热捕获和全球变暖增加。IPCC第六次评估报告（IPCC，2022）强烈建议将全球变暖限制在比工业化前水平高1.5ºC，以避免严重的气候变化影响。这将需要在2030年之前将全球二氧化碳排放量减半，并在2050年之前将其削减至净零，以及每年额外消除20-100亿公吨（Gt）的二氧化碳。在某些地方，气候变暖可能有利于某些作物，而且随着时间的推移，最佳的种植区域可能会远离赤道而转移。然而，气候变化的影响并不限于世界上许多地方的温度上升和热浪，还包括降雨量的变化、更严重和更频繁的风暴、干旱的增加以及野火的威胁增加。所有这些影响预计将在未来20年内对全世界的作物产量和粮食安全产生不利影响（Zhao et al, 2017; Li et al, 2019; Jägermeyr et al, 2021）。随着气候变化对作物系统的影响加剧，开发抗逆性作物以应对粮食不安全的需求也随之上升。
在这篇文章中，我们探讨了植物科学家正在研究与碳封存有关的解决方案的几种方式，以帮助实现二氧化碳的净零排放，并改进作物，以保护和提高产量，增加粮食安全。第一部分概述了提高作物（一年生和多年生）和海草的碳封存能力的挑战和方法，接着是关于改善光合作用的部分。第三部分讨论了作物的气候复原力工程（对非生物和生物压力的抗性或耐受性）。最后一节描述了扎根于植物生物学的可持续全球生物经济的愿景。我们承认，还有其他一些领域，包括生物能源、林业和生态系统保护，植物科学可以在这些领域发挥缓解气候变化不利影响的作用，但在这里没有涉及。所有这些领域的解决方案都需要在不久的将来和较长的时间内完成。我们不提供对这些主题的深入审查。相反，这里提供的例子说明了世界各地的植物科学家正在进行的许多研究途径中的几个。Verslues等人（2023）的一篇配套综述讨论了植物非生物胁迫方面尚未解决的问题。我们希望这些故事能够帮助植物科学界了解各种可能性，刺激进一步的研究，并激励处于职业生涯任何阶段的植物科学家参与到旨在缓解气候变化、提高粮食和能源安全的工作中。缓解气候变化的危机需要所有的人一起努力。
研究内容:
1. 如何将更多的碳保留在土壤和生物质中？
2. 一年生作物系统中的碳封存
3. 利用植物的力量：加强植物固碳的全球倡议
4. 多年生作物的快速从头驯化
5. 海草对碳捕获和储存的承诺
6. 我们知道什么？
7. 我们不知道什么
8. 围绕未知的机会
Figure 1 Quantitative variation in lignin content in maize root systems
from a field study of 358 maize inbred lines. A description of the
experiment can be found in Woods et al. (2022).
Figure 2 Toward an ideal carbon-capturing crop plant. A, The ideal plant should accumulate suberin in the cell wall of its root cells and form a vast and deep root system. To realize this goal, the existing literature and experimental evidence are curated to look for candidate genes affecting root system architecture and root mass. This information is combined with root-specific promoters and suberin biosynthetic genes. B, The ideal plant is created by capitalizing on both classical (breeding) and more recent (genome editing, genetic engineering) approaches to introduce favorable alleles and genes that will increase root biomass and transgenes that will increase the deposition of suberin in the root. In addition to trapping more carbon, these ideal plants will replenish carbon-depleted soils with degradation-recalcitrant carbon polymers (indicated by the darker color of the soil on the right). Figure credit: P. Salome´.
Figure 3 Examples of wide hybridization and direct domestication to develop perennial grains. The wild perennial Sorghum halepense (A) was hybridized with the domestic species Sorghum bicolor (B) and selective breeding of the progeny produced lines with intermediate head and seed size (C) and the ability to regrow from underground rhizomes (D). In an example of direct domestication, the mostly wild grass Thinopyrum intermedium can be harvested with conventional equipment (E) and cleaned to obtain a human-edible grain (F) that has properties similar to wheat, as seen in this loaf made with an 80/20 blend of wheat and Th. intermedium flour (G). Domesticated Th. intermedium types now possess domestication traits, such as shatter resistance (H, at right).
Figure 4 Synthetic biology approaches for recycling photorespiration and CO2-fixation pathways. A and B, Photorespiration engineered for breakdown of one glycolate to two CO2 molecules (A) or conversion of two glycolate to one glycerate plus one CO2 molecule (B). The CO2 released in the chloroplast is recycled back to the CBB cycle for carbon reassimilation (Maier et al., 2012; Shen et al., 2019; South et al., 2019). C, The MCG-cycle engineered to convert glycolate to acetyl-CoA without carbon loss (Yu et al., 2018b). D, Creation of a new enzyme, such as glycolyl-CoA carboxylase, to achieve glycolate recycling to produce glycerate with input of ATP and an additional CO2 molecule (Scheffen et al., 2021). E, Rubiscoindependent CETCH and rPS-MCG synthetic CO2-fixation pathways (Luo et al., 2022).
Figure 5 Schematic diagram showing average annual atmospheric [CO2] level for 2021 and the effect of rising night temperature (Tmin) on rice productivity by enhanced respiration: photosynthesis ratio (RN/A) resulting in augmented release of carbon at the cost of biomass and yield in conventional genotypes. On the contrary, introgression of CO2-responsiveness trait in C3 crops facilitates enhanced carbon sequestration and allocation of additional carbon into biomass, and compensating Tmin-induced carbon losses. LCR, least CO2-responsive; HCR, high CO2-responsive.
Figure 6 Schematics of C3 CBB and NADP-ME C4 Cycles. A, CBB C3 cycle. B, NADP-ME C4 cycle. C, Transverse leaf sections and corresponding schematics of C3 rice (left) and C4 maize (right). Bars = 30 lm. Adapted from Langdale (2011), Figures 1 and 3.
Figure 7 The Trait Development Pipeline for delivery of valuable stress tolerance traits/genes/QTLs from upstream research into the elite breeding pool for improvement of crop productivity under climate change. The Trait Development Pipeline is organized into six stages: 1) guidelines for prioritizing traits (assessment), 2) defining standards for phenotyping protocols, 3) identifying donors and QTL (including refining marker quality metrics), 4) introgressing and 5) validating traits/genes/QTLs into elite genetic backgrounds to develop the elite donor lines that are 6) handed to the breeding program for crossing. Those elite donor lines will then be systematically crossed and tested in target environments where climate change is increasingly affecting the degree of abiotic stress affecting crop production. Created with BioRender.com
Figure 8 Development of crops with enhanced resilience to abiotic and biotic stress. Crops are exposed to a variety of stresses. Abiotic stresses will intensify as the following climate conditions change: water availability, precipitation, temperatures, and atmospheric CO2 levels. Biotic stressors that plants encounter will vary, but may consist of: bacteria, fungi, oomycetes, nematodes, viruses, and insect pests. As climate change alters environmental conditions and plant-pathogen interactions, strategies to develop more climate-ready and disease-resistant crop varieties include breeding or genome engineering approaches with stacking disease resistance genes, stacking climate tolerance and disease resistance genes, and/ or addition of beneficial microbes (see text for examples).
Figure 9 Mycorrhizal symbiosis and N self-fertilizing crops. A, Positive effects of mycorrhizal symbiosis. The mycorrhizal hyphal network forms a mycorrhizosphere (light brown) which can enlarge the plant nutrient absorption area and supply a convenient zone for root-related microbes. Benefits from mycorrhizal symbiosis include increased tolerance or resistance to abiotic or biotic stresses. B, Three steps to develop N self-fertilizing cereal crops to enhance climate change resilience. (1) Increasing associative N fixation. The mucilage (light green) is rich in carbohydrates and harbors abundant diazotrophic microbiota (pink). Engineered cereal plants (such as maize) have the ability to produce rhizophine, which can be perceived by engineered diazotrophs (orange). (2) Transferring symbiotic N fixation to cereal plants. Cereal crops are engineered for symbiotic N fixation by expressing the chimeric receptors perceiving rhizobia signals and overexpressing key symbiotic regulators (CSSP genes, CRE1, etc.) and nodule development genes (SCR-SHR, LBD16, etc.) to form nodule-like structures. (3) Autonomous N fixation in cereal crops. The ideal plant which could assimilate N2 into ammonium is created by overexpressing rhizobial N fixation genes in plant cells.
Figure 10 Genomic selection (GS) in a cassava breeding program. A, Each breeding cycle begins with a crossing block trial where seeds are generated. The first evaluation, a seedling nursery (SDN) usually involves 410K plants, but cassava does not produce storage roots when planted from seed and no yield data is collected. After 12 months, seedlings are cloned (5–10 cuttings/plant) into their first single-row, unreplicated clonal evaluation trial (CET) followed by at least three stages of yield trials (preliminary [PYT], advanced [AYT], and uniform [UYT]). All lines entering CET are genotyped genome-wide; sometimes this is done during the seedling nursery. As a result, genomic prediction enables selection of new parents for crossing even as early as the SDN (dashed red arrow). B, GS has resulted in demonstrable acceleration in the rate of genetic improvement since initiation in 2012. Results shown are from the IITA GS population. The genomically predicted performance of GS-era (purple) and historical (yellow) clones relative to a multi-trait selection index (y-axis) is plotted against the year when each clone was first generated (x-axis). C, Field trial showing variability for one of the major future challenges to cassava: drought. The top image shows plants 3 months after planting, under irrigation at Petrolina (Pernambuco, Brazil). The bottom image shows plants 3 months later under water deficit.
研究结论：
我们介绍了一些基于植物生物学的解决方案的例子，我们认为这些解决方案在加强陆地碳固存和工程气候适应性作物方面显示出前景。尽管我们讨论了几个不同的主题，但还是得出了一些总体性的结论。
在今天的读者看来，这里描述的一些想法可能很牵强，但我们相信，为了让我们的地球保持可居住和可持续发展，这里提出的许多想法--或者其他类似的想法--都需要实现，而我们需要植物科学家来帮助实现这些目标。
根据定义，缓解全球气候变化的努力必须是大规模的。在这个领域做出有意义贡献的植物科学家很可能是那些寻求有效合作的人--不仅与其他植物科学家合作，而且还与其他学科的科学家合作，例如农学、生物信息学、数据科学、工程学、林业和土壤科学。改善跨学科以及学术界和产业界之间的交流与合作，也可以看作是一种可以产生强大影响的低技术工作。在研究项目的早期规划阶段，确定并寻求能够将研究与有影响的途径联系起来的潜在合作者，应该是一个首要目标，以获得最大的利益。社会经济和政治观点也将是决定哪些方法将被采用以及如何快速实施的关键。在社会政治领域以及与工业界、政府和非政府组织的联网、讨论和合作也可能是至关重要的。
目前的许多做法在减少二氧化碳排放方面有很大的潜力，包括减少食物和农业废物，转向以植物为基础的饮食，减少森林砍伐加上造林/再造林，以及恢复沿海湿地。一些技术解决方案在短期内也有潜力，包括直接空气捕捉、生物炭、增强岩石风化、以及结合碳捕捉和储存的生物能源。迄今为止，由于成本、时间表、效率低下、缺乏可扩展性或不确定和不断变化的碳价格和市场，这些方案都没有在全球范围内实施。对现有技术潜力的估计差异很大，将取决于各国实现有效措施的能力（Roe等人，2019）。我们已经探讨了植物科学可以帮助将天平转向加强气候变化缓解和作物抗灾能力的方法。关于在一年生作物系统中加强碳捕获和封存的部分谈到了我们对大规模碳捕获的迫切需求，以及植物科学家在这一领域实现有意义影响的可能性。
所讨论的一些例子的目标可能需要多年才能完全实现，如将C4光合作用工程化到水稻中，将共生氮固定到谷类中，以及生产各种合成产品的作物。虽然时间紧迫，但这并不意味着它们不值得关注。首先，这些长期目标的某些方面可能会在短期内带来巨大的利益，其次，未来将继续需要碳捕获和增强作物的复原力和粮食安全。今天，每一位植物生物学家都迫切需要考虑他们的研究如何为应对气候变化、确保粮食安全和实现可持续的生物质生物经济作出贡献。
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