As one of the grave environmental hazards, soil salinization seriously limits crop productivity, growth, and development. When plants are exposed to salt stress, they suffer a sequence of damage mainly caused by osmotic stress, ion toxicity, and subsequently oxidative stress. As sessile organisms, plants have developed many physiological and biochemical strategies to mitigate the impact of salt stress. These strategies include altering root development direction, shortening the life cycle, accelerating dormancy, closing stomata to reduce transpiration, and decreasing biomass. Apart from being a prime energy source, light is an environmental signal that profoundly influences plant growth and development and also participates in plants' response to salt stress. This review summarizes the regulatory network of salt tolerance by light signals in plants, which is vital to further understanding plants' adaptation to high salinity. In addition, the review highlights potential future uses of genetic engineering and light supplement technology by light-emitting diode (LED) to improve crop growth in saline-alkali environments in order to make full use of the vast saline land.

INTRODUCTION:The yield and quality of tomato (Solanum lycopersicum. L) are often decreased when plants suffer from low light intensity and short-photoperiod in winter. Manipulation of the artificial light environment is a feasible technology to promote off-seasonal production and improve fruit nutritional quality in the greenhouse. OBJECTIVES:Here we aim to investigate the appropriate balance between red (R) and blue (B) light to improve tomato yield and quality traits. METHODS:Biochemical, molecular and genetic analysis were used to study the photosynthetic traits, pigments, sugar and volatile accumulation pathway genes. RESULTS:Tomato plants subjected to R1B0.8, a ratio between monochromatic red (R) and blue (B) light, for 16 h photoperiod showed significantly increased chlorophyll and biomass accumulation compared to white (W) light treatment. R1B0.8 light treatment enhanced electron transfer efficiency and photosynthetic capacity by improving the light energy utilization rate and inducing photosystem core subunit genes (SlPsaC, SlPsaB, SlPsaA) and light-harvesting complex genes (SlLHCB/A). Compared to W light, R1B0.8 light also induced carotenoid accumulation and accelerated fruit ripening, which was associated with the upregulation of carotenoid biosynthesis genes (SlPSY1, SlPDS) and ethylene biosynthesis genes (SlACS2, SlACO2) in tomato fruits. Moreover, fruits exposed to R1B0.8 light treatments significantly improved fructose and glucose accumulation and the expression of the volatile-related gene (SlAADC1a) and flavor-related gene (SlGORKY). CONCLUSION:Our results showed that R1B0.8 light with a 16 h photoperiod could prominently promote photosynthetic traits, pigments, sugar and volatile accumulation in tomato. Our findings on the manipulation of artificial light environments in protected horticulture offer possibilities for enhancing crop yield and quality to meet the increasing global demand for food.

Cold stress is a key environmental constraint that dramatically affects the growth, productivity, and quality of tomato (Solanum lycopersicum); however, the underlying molecular mechanisms of cold tolerance remain poorly understood. In this study, we identified REDUCED CHLOROPLAST COVERAGE 2 (SlREC2) encoding a tetratricopeptide repeat protein that positively regulates tomato cold tolerance. Disruption of SlREC2 largely reduced abscisic acid (ABA) levels, photoprotection, and the expression of C-REPEAT BINDING FACTOR (CBF)-pathway genes in tomato plants under cold stress. ABA deficiency in the notabilis (not) mutant, which carries a mutation in 9-CIS-EPOXYCAROTENOID DIOXYGENASE 1 (SlNCED1), strongly inhibited the cold tolerance of SlREC2-silenced plants and empty vector control plants and resulted in a similar phenotype. In addition, foliar application of ABA rescued the cold tolerance of SlREC2-silenced plants, which confirms that SlNCED1-mediated ABA accumulation is required for SlREC2-regulated cold tolerance. Strikingly, SlREC2 physically interacted with β-RING CAROTENE HYDROXYLASE 1b (SlBCH1b), a key regulatory enzyme in the xanthophyll cycle. Disruption of SlBCH1b severely impaired photoprotection, ABA accumulation, and CBF-pathway gene expression in tomato plants under cold stress. Taken together, this study reveals that SlREC2 interacts with SlBCH1b to enhance cold tolerance in tomato via integration of SlNCED1-mediated ABA accumulation, photoprotection, and the CBF-pathway, thus providing further genetic knowledge for breeding cold-resistant tomato varieties.

光作为重要的环境因子之一,不仅为植物光合作用提供能量,而且作为信号影响植物对外界环境的响应.该文综述了红光和远红光对植物生长发育和非生物胁迫响应的调控作用,重点阐述了光敏色素及下游光信号转录因子整合激素等内源信号调控植物种子萌发、下胚轴伸长、芽发育及开花的分子机制,以及红光和远红光在植物响应盐、干旱及温度胁迫中的作用机制.在挖掘植物感知和响应光环境机理的基础上,利用LED光谱技术对作物进行精确补光,有望提高作物产量、品质和抗逆性,同时推进实现"双碳"目标,减少能源消耗和环境污染.

Increasing photosynthesis and light capture offers possibilities for improving crop yield and provides a sustainable way to meet the increasing global demand for food. However, the poor light transmittance of transparent plastic films and shade avoidance at high planting density seriously reduce photosynthesis and alter fruit quality in vegetable crops, and therefore it is important to investigate the mechanisms of light signaling regulation of photosynthesis and metabolism in tomato (Solanum lycopersicum). Here, a combination of red, blue, and white (R1W1B0.5) light promoted the accumulation of chlorophyll, carotenoid, and anthocyanin, and enhanced photosynthesis and electron transport rates by increasing the density of active reaction centers and the expression of the genes LIGHT-HARVESTING COMPLEX B (SlLHCB) and A (SlLHCA), resulting in increased plant biomass. In addition, R1W1B0.5 light induced carotenoid accumulation and fruit ripening by decreasing the expression of LYCOPENE β-CYCLASE (SlCYCB). Disruption of SlCYCB largely induced fruit lycopene accumulation, and reduced chlorophyll content and photosynthesis in leaves under red, blue, and white light. Molecular studies showed that ELONGATED HYPOCOTYL 5 (SlHY5) directly activated SlCYCB, SlLHCB, and SlLHCA expression to enhance chlorophyll accumulation and photosynthesis. Furthermore, R1W1B0.5 light-induced chlorophyll accumulation, photosynthesis, and SlHY5 expression were largely decreased in the slphyb1cry1 mutant. Collectively, R1W1B0.5 light noticeably promoted photosynthesis, biomass, and fruit quality through the photoreceptor (SlPHYB1 and SlCRY1)-SlHY5-SlLHCA/B/SlCYCB module in tomato. Thus, the manipulation of light environments in protected agriculture is a crucial tool to regulate the two vital agronomic traits related to crop production efficiency and fruit nutritional quality in tomato.

Plants have evolved sophisticated regulatory networks to cope with dynamically changing light and temperature environments during day-night and seasonal cycles. However, the integration mechanisms of light and low temperature remain largely unclear. Here, we show that low red : far-red ratio (LR : FR) induces FAR-RED ELONGATED HYPOCOTYL3 (SlFHY3) transcription under cold stress in tomato (Solanum lycopersicum). Reverse genetic approaches revealed that knocking out SlFHY3 decreases myo-inositol accumulation and increases cold susceptibility, whereas overexpressing SlFHY3 induces myo-inositol accumulation and enhances cold tolerance in tomato plants. SlFHY3 physically interacts with ELONGATED HYPOCOTYL5 (SlHY5) to promote the transcriptional activity of SlHY5 on MYO-INOSITOL-1-PHOSPHATE SYNTHASE 3 (SlMIPS3) and induce myo-inositol accumulation in tomato plants under cold stress. Disruption of SlHY5 and SlMIPS3 largely suppresses the cold tolerance of SlFHY3-overexpressing plants and myo-inositol accumulation in tomato. Furthermore, silencing of SlMIPS3 drastically reduces myo-inositol accumulation and compromises LR : FR-induced cold tolerance in tomato. Together, our results reveal a crucial role of SlFHY3 in LR : FR-induced cold tolerance in tomato and unravel a novel regulatory mechanism whereby plants integrate dynamic environmental light signals and internal cues (inositol biosynthesis) to induce and control cold tolerance in tomato plants.

Perceiving incoming environmental information is critical for optimizing plant growth and development. Multiple B-box proteins (BBXs) play essential roles in light-dependent developmental processes in plants. However, whether BBXs function as a signal integrator between light and temperature in tomato plants remains elusive. In this study, 31 SlBBX genes were identified from the newly released tomato (Solanum lycopersicum) genome sequences and were clustered into five subgroups. Gene structure and protein motif analyses showed relatively high conservation of closely clustered SlBBX genes within each subgroup; however, genome mapping analysis indicated the uneven distribution of the SlBBX genes on tomato chromosomes. Promoter cis-regulatory elements prediction and gene expression indicated that SlBBX genes were highly responsive to light, hormones, and stress conditions. Reverse genetic approaches revealed that disruption of SlBBX7, SlBBX9, and SlBBX20 largely suppressed the cold tolerance of tomato plants. Furthermore, the impairment of SlBBX7, SlBBX9, and SlBBX20 suppressed the photosynthetic response immediately after cold stress. Due to the impairment of non-photochemical quenching (NPQ), the excess photon energy and electron flow excited by low temperature were not consumed in SlBBX7-, SlBBX9-, and SlBBX20- silenced plants, leading to the over reduction of electron carriers and damage of the photosystem. Our study emphasized the positive roles of light signaling transcription factors SlBBXs in cold tolerance in tomato plants, which may improve the current understanding of how plants integrate light and temperature signals to adapt to adverse environments.

花青素是植物中一类重要的类黄酮化合物,在植物花朵、果实等器官色泽形成和抗氧化过程中起着重要作用.植物组织中花青素的形成依赖于光信号,但是光信号对花青素生物合成的调控机制及信号网络很大程度上还不清晰.本文简述了花青素生物合成及运转过程的研究进展,简要归纳了MYB、bHLH、WDR三类主要因子对花青素合成的转录调控作用,重点阐释光信号(光强、光质、光照时长)对植物花青素合成的调控作用.研究表明,光环境(光强、光质、光照时长)主要通过不同的光受体(UVR8、CRYs、PHOTs、PHYs)影响光信号通路重要因子COP1的泛素化能力和HY5的稳定性,以及其他光信号转录因子如光敏色素互作因子PIFs的稳定性,进而调控花青素的生物合成过程.这些光信号因子一方面直接结合到调控花青素合成的MYB、bHLH、WDR三大类转录因子上,转录激活或抑制它们的表达进而调控花青素的合成;另一方面,这些光信号因子通过与MYB、bHLH、WDR三大类转录因子蛋白互作,影响它们形成的MBW复合体稳定性,进而调控花青素的合成.此外,这些光信号因子还可以通过不依赖于MBW复合体的通路调控花青素的合成,如HY5通过调控miR858影响花青素的生物合成;另外,一些未知的光响应因子可能以不依赖MBW通路的方式直接或间接地调控花青素合成基因和液泡膜上的运转蛋白,改变液泡酸化,调节花青素的合成.同时,光信号会影响光合电子传递,光合电子传递链中的一些因子也会通过依赖和不依赖MBW的途径影响植物花青素的合成.这些途径如何协调以及哪些信号因子优先受光环境(光强、光质、光照时间)调控?本文为深入研究光信号对花青素生物合成的调控机理提供参考,以探索光调控花青素积累的有效途径及靶标分子,为利用基因工程、代谢工程和光环境调控手段改良园艺植物花青素积累提供理论基础.

Plants experience low ambient temperature and low red to far-red ratios (L-R/FR) of light due to vegetative shading and longer twilight durations in cool seasons. Low temperature induce photoinhibition through inactivation of the photosynthetic apparatus, however, the role of light quality on photoprotection during cold stress remains poorly understood. Here, we report that L-R/FR significantly prevents the overreduction of the entire intersystem electron transfer chain and the limitation of photosystem I (PSI) acceptor side, eventually alleviating the cold-induced photoinhibition. During cold stress, L-R/FR activated cyclic electron flow (CEF), enhanced protonation of PSII subunit S (PsbS) and de-epoxidation state of the xanthophyll cycle, and promoted energy-dependent quenching (qE) component of non-photochemical quenching (NPQ), enzyme activity of Foyer-Halliwell-Asada cycle and D1 proteins accumulation. However, L-R/FR -induced photoprotection pathways were compromised in tomatoPROTON GRADIENT REGULATION5(PGR5) andPGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1A(PGRL1A) co-silenced plants andNADH DEHYDROGENASE-LIKE COMPLEX M(NDHM) -silenced plants during cold stress. Our results demonstrate that both PGR5/PGRL1- and NDH-dependent CEF mediate L-R/FR -induced cold tolerance by enhancing the thermal dissipation and the repair of photodamaged PSII, thereby mitigating the overreduction of electron carriers and the accumulation of reactive oxygen species. The study indicates that there is an anterograde link between photoreception and photoprotection in tomato plants during cold stress.

总结了光信号(光强、光质、光周期及昼夜节律中光暗变化)对叶绿素含量及其生物合成途径中相关基因的影响.重点归纳了光信号途径中主要转录因子对叶绿素合成基因的调控机制,强调了表观遗传修饰在光调控叶绿素合成中的重要作用,以期探索光调控叶绿素积累的有效途径及靶标分子,为利用基因工程和环境调控手段定向调控有重要生物学功能的叶绿素提供理论基础.