Sunburn, a physiological disorder caused by intense light and high-temperature stress, significantly reduces the yield and quality of ponkan fruit. However, the coordinated roles of photo-protective mechanisms and antioxidative defense systems in mitigating sunburn damage under such stress remain poorly understood. In this study, transcriptome analysis revealed that in mild and moderate sunburn peels, the expression of carotenoid biosynthesis genes (CsPSY, CsCRTISO, CsLCYB, CsHYB), particularly those associated with the xanthophyll cycle (CsVDE), were up-regulated, while carotenoid degradation genes (CsCCD, CsNCED) were down-regulated. Consequently, 15 carotenoids (including 12 carotenoid fatty acid esters) showed significant accumulation. Notably, the xanthophyll cycle pool size increased dramatically in mild sunburn peel. Concurrently, reactive oxygen species (ROS), including superoxide anion (O2·ˉ) and hydrogen peroxide (H2O2), accumulated, accompanied by the up-regulation of antioxidative genes (CsSOD, CsGPX, CsAPX, CsMDHAR). This enhanced the activity of related antioxidative enzymes and the efficiency of the ascorbate to glutathione (AsA-GSH) cycle in sunburn peels. Furthermore, levels of ascorbate (AsA) and glutathione (GSH), and redox ratios [AsA/(AsA+DHA) and GSH/(GSH+GSSG)] increased substantially in sunburn peels. Interestingly, mild and moderate sunburn symptoms were reversible after 20 days of shading with a black net, whereas severe sunburn resulted in irreversible cell browning and necrosis. These findings suggest that the xanthophyll cycle, carotenoid biosynthesis, and AsA-GSH cycle act synergistically to alleviate oxidative stress in ponkan fruit peel under intense light and high-temperature conditions. This study offers critical insights into photo-protective and antioxidative defense mechanisms and provides a foundation for breeding sunburn-tolerant ponkan cultivars in the future.

ABSTRACT To explore the effects of salicylic acid (SA) on the softening of postharvest grapes, “Red Globe” grapes (Vitis vinifera L.) were immersed in 1.0 mM SA for 5 min and stored at 4°C for 56 days. Results revealed that SA treatment could maintain cell wall component contents by inhibiting enzyme activities and gene expression, including pectin methyl esterase, polygalacturonase, and β‐galactosidase. Meanwhile, SA application delayed the degradation of wax crystals and maintained higher levels of wax fractions. In addition, SA treatment upregulated the transcription of genes involved in the phenylpropanoid pathway, resulting in higher endogenous phenolics. In conclusion, SA treatment effectively delayed softening by regulating cell wall, cuticular wax, and phenylpropanoid metabolism. These findings provide a theoretical basis for clarifying the mechanism by which SA maintains the fruit quality of grapes, and support the use of exogenous SA as a strategy to extend shelf life and improve fruit quality in commercial storage.

Abstract Heat stress poses a major threat to global crop productivity, with the male gametophyte being the most thermosensitive stage. While peptide hormones are known orchestrators of plant vegetative adaptation, their roles in reproductive thermotolerance remain largely undefined. Here, we show that phytosulfokine (PSK) signaling determines tomato pollen thermotolerance, as heat-induced anther PSK precursor expression correlates with pollen germination, and exogenous PSK application mitigates heat-induced pollen abortion. Loss of the PSK receptor PSKR1 or the NADPH oxidase Respiratory burst oxidase homolog B (RBOHB) compromises reactive oxygen species (ROS) homeostasis and pollen thermotolerance, causing severe yield losses under both controlled and natural field heat-stress conditions. Mechanistically, genetic rescue experiments establish that RBOHB-dependent ROS signaling functions downstream of PSK perception driven by PSKR1-mediated phosphorylation of RBOHB at Threonine-266 and Serine-340 in pollen grains, which triggers protective ROS bursts to activate the downstream heat shock transcription factors/heat shock proteins (HSF/HSP) pathway. Genetic complementation with phospho-mimic variants confirms that phosphorylation at these residues is sufficient to enhance pollen thermotolerance. Our findings define a PSK peptide-ROS signaling axis that safeguards male thermotolerance, providing both genetic targets and peptide-based strategies for sustaining crop yields in a warming climate.

Peel color in citrus is largely genetically controlled. Red peel is favored by customers and is important, therefore, for fruit external quality. In order to understand the factors affecting distribution of carotenoids and color intensity of red-peeled citrus, we compared carotenoid accumulation and gene expression in the peel of twelve fully ripe red-peeled citrus cultivars with different genetic backgrounds. The results showed that β-citraurin, a red C30 carotenoid, was the second or third most abundant colored carotenoid in the peel of all twelve red-peeled citrus, ranging from 9.4 % to 26.7 % of total carotenoids. Statistical analysis of carotenoid composition and content showed that of the main carotenoids β-citraurin had the highest correlation with red appearance of cultivars. In addition, β-cryptoxanthin, which accounted for 3.6 % to 16.4 % of the total carotenoids, were also significantly positively correlated with citrus color index (CCI). The expression of two key genes, phytoene synthase 1 (PSY1) and carotenoid cleavage dioxygenase 4b1 (CCD4b1), differed among cultivars with a range of 3.5- and 48.8-fold, respectively. Surprisingly, accumulation of total carotenoids and β-citraurin was not correlated with the expression of PSY1 and CCD4b1, respectively, implying that diverse factors influence high carotenoid accumulation in red-peeled citrus.

The impact of low light intensities on plant disease outbreaks represents a major challenge for global crop security, as it frequently results in significant yield losses. However, the underlying mechanisms of the effect of low light on plant defense are still poorly understood. Here, using an RNA-seq approach, we found that the susceptibility of tomato to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) under low light was associated with the oxidation-reduction process. Low light conditions exacerbated Pst DC3000-induced reactive oxygen species (ROS) accumulation and protein oxidation. Analysis of gene expression and enzyme activity of ascorbate peroxidase 2 (APX2) and other antioxidant enzymes revealed that these defense responses were significantly induced by Pst DC3000 inoculation under normal light, whereas these genes and their associated enzyme activities were not responsive to pathogen inoculation under low light. Additionally, the reduced ascorbate to dehydroascorbate (AsA/DHA) ratio was lower under low light compared with normal light conditions upon Pst DC3000 inoculation. Furthermore, the apx2 mutants generated by a CRISPR-Cas9 gene-editing approach were more susceptible to Pst DC3000 under low light conditions. Notably, this increased susceptibility could be significantly reduced by exogenous AsA treatment. Collectively, our findings suggest that low-light-induced disease susceptibility is associated with increased cellular oxidative stress in tomato plants. This study sheds light on the intricate relationship between light conditions, oxidative stress, and plant defense responses, and may pave the way for improved crop protection strategies in low light environments.

Pipecolic acid (Pip) and N-hydroxypipecolic acid (NHP) have been found to accumulate during the ripening of multiple types of fruits; however, the function and mechanism of pipecolate pathway in fruits remain unclear. Here study was conducted on fruits produced by the model plant tomato, wherein the NHP biosynthesis-related genes, Slald1 and Slfmo1, were mutated. The results showed that the fruits of both the Slald1 and the Slfmo1 mutants exhibited a delayed onset of ripening, decreased fruit size, nutrition and flavor. Exogenous treatment with Pip and NHP promoted fruit ripening and improved fruit quality. Transcriptomic analysis combined with weighted gene co-expression network analysis revealed that the genes involved in the biosynthesis of amino acids, carbon metabolism, photosynthesis, starch and sucrose metabolism, flavonoid biosynthesis, and plant hormone signal transduction were affected by SlFMO1 gene mutation. Transcription factor prediction analysis revealed that the NAC and AP2/ERF-ERF family members are notably involved in the regulation pathway. Overall, our results suggest that the pipecolate biosynthesis pathway is involved in the simultaneous regulation of fruit ripening and quality and indicate that a regulatory mechanism at the transcriptional level exists. However, possible roles of endogenously synthesized Pip and NHP in these processes remain to be determined. The biosynthesis pathway genes SlALD1 and SlFMO1 may be potential breeding targets for promoting fruit ripening and improving fruit quality with concomitant yield increases.

【Background】With global climate change, the increase of atmospheric CO2 concentration is predicted to exert an influence on plant diseases, which seriously affects agricultural production. Plant β-carbonic anhydrases (βCAs) are important components in plant CO2 sensing and concentration systems and are involved in the immunity of Arabidopsis and tobacco. However, little is known about the functions of βCAs in the regulation of disease resistance in tomato (Solanum lycopersicum).【Objective】The objective of this study is to explore the role and mechanism of tomato SlβCA3 in disease resistance, so as to provide scientific basis for resistance regulation of tomato in agricultural production.【Method】Based on the similarity to the amino acid sequences of AtβCAs, four SlβCAs were identified in the Sol genomics network database. Wild-type (WT) tomato ‘Ailsa Craig’ (AC) was used to inoculate Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) in the study. Then qRT-PCR was used to determine the transcript abundance of SlβCAs in leaves to screen the Pst DC3000-induced gene SlβCA3. Furthermore, SlβCA3 stable over-expression lines (OE-SlβCA3) were generated by Agrobacterium tumefaciens-mediated genetic transformation technology as the background of AC. OE-SlβCA3 plants were inoculated with Pst DC3000 to investigate the role of SlβCA3 in disease defense. For exploring the intrinsic mechanism of SlβCA3 regulating plant disease resistance, the transcriptome changes of WT and OE-SlβCA3 plants between inoculation with Pst DC3000 and control conditions were compared, and KEGG (Kyoto encyclopedia of genes and genomes) database was used to analyze functions of the differentially expressed genes. It is speculated that sugar metabolism pathways are involved in SlβCA3-mediated plant immunity. To verify and further analyze the conclusion, the expression of genes related to the sugar metabolism and signaling, as well as the contents of glucose, fructose and sucrose in WT and OE-SlβCA3 plants were determined.【Result】OE-SlβCA3 plants enhanced the resistance to Pst DC3000, and showed less disease-associated cell death and a lower number of bacteria compared to the WT controls. RNA-Seq results showed that OE-SlβCA3 did not greatly change the overall transcript profile in the absence of the pathogen. In total, 2 100 Pst DC3000-induced transcripts were differentially changed in abundance. Of these, 63.3% were more abundant following Pst DC3000 inoculation in the OE-SlβCA3 plants. KEGG analysis showed that Pst DC3000-induced genes, which are dependent on SlβCA3-overexpression, were enriched in the pathways related to sugar metabolism, including starch and sucrose metabolism, protein processing in the endoplasmic reticulum (glycosylation), amino sugar and nucleotide sugar metabolism, ribosomal biosynthesis in eukaryotes and photosynthesis. Sugar metabolism is closely related to sugar signaling. Further studies found that the expression of genes related to sugar metabolism and signal transduction pathways, as well as the contents of glucose, fructose and sucrose, were higher in the leaves of OE-SlβCA3 plants than those of WT after inoculation with Pst DC3000.【Conclusion】Overexpression of SlβCA3 in tomato enhances the resistance of plants to Pst DC3000, which may be related to the role of sugar metabolism and signaling in plant immunity.

[背景]番茄(Solanum lycopersicum)作为连续发芽分化和坐果的重要园艺作物,早衰是限制其生长期长短、产量和品质的重要因素.NAC(NAM、ATAF1/2和CUC2)转录因子家族参与调控拟南芥,水稻等多种植物衰老进程,但在番茄中的研究尚不深入.目前已知,SlNAP2(NAC-like,activated by apetala3/pistillata)参与番茄植株衰老进程.[目的]S1NAC29为S1NAP2的同源基因,对其在番茄植株衰老中的功能及调控机制进行研究,以期为园艺栽培中番茄的衰老调控及种质创新提供科学依据.[方法]以野生型番茄(CondineRed,CR)为背景,采用qRT-PCR技术明确S1NAC29在不同衰老阶段叶片中的相对表达量,并分别利用CRISPR/Cas9基因编辑技术和基因过表达技术构建Slnac29纯合突变体及OE:S1NAC29稳定过表达植株.在此基础上,在自然生长状态下和黑暗处理诱导衰老条件下,对野生型、Slnac29突变体和OE:S1NAC29过表达植株的生长、叶绿素含量、光合作用、叶片衰老和叶绿素降解相关基因的相对表达量等参数进行分析,明确S1NAC29转录因子在调控番茄植株衰老中的生物学功能;进一步利用聚类热图分析过表达植株OE:S1NAC29中29个衰老相关基因、叶绿素降解基因以及ABA合成/信号转导相关基因的相对表达量.并选取在黑暗诱导衰老条件下不同株系植株中表达差异明显的4个基因进行凝胶迁移阻滞分析(electrophoretic mobility shift analysis,EMSA),以鉴定S1NAC29直接转录调控的靶标基因及其与衰老调控的关系.[结果]S1NAC29在初老叶和衰老叶片中的相对表达量较嫩叶和成熟叶显著上升.自然生长状态下,突变体材料Slnac29与野生型长势以及光合速率无明显差异,而过表达材料OE:S1NAC29株高则显著低于野生型植株,叶绿素含量和光合速率分别是野生型植株的25％和50％.在黑暗诱导衰老的条件下,野生型植株叶片明显变黄,叶绿素含量显著下降.Slnac29突变缓解了叶片衰老程度,叶片无明显变黄,叶绿素含量是野生型的3倍,衰老相关基因(senescence-associated genes,SAGs)和叶绿素降解基因的表达量均较低.OE:S1NAC29则相反,叶片衰老程度比野生型和Slnac29突变体均明显严重.基因聚类分析表明多个衰老相关基因和叶绿素降解基因在OE:S1NAC29植株中显著上调表达.EMSA鉴定到S1NAC29能够直接与衰老相关基因家族SAGs成员S1AGT1(Glyoxylate aminotransferase)启动子绑定,且S1AGT1在OE:S1NAC29中的相对表达量较野生型和Slnac29突变体显著增加.[结论]转录因子S1NAC29调控番茄植株的衰老,促进番茄叶片在黑暗诱导条件下的衰老进程.S1NAC29直接绑定衰老相关基因S1AGT1启动子区域调控其转录表达.

With global warming and water shortage, drought stress is provoking an increasing impact on plant growth, development, and crop productivity worldwide. Pipecolic acid (Pip) is an emerging lysine catabolite in plants, acting as a critical element in disease resistance with a related signal pathway of phytohormone salicylic acid (SA). While SA plays a vital role in various abiotic stresses, the role of Pip in plant response to abiotic stresses, especially drought, remains largely unknown. To address this issue, Pip biosynthetic gene Slald1 mutants and hydroxylated modification gene Slfmo1 mutants were generated using CRISPR-Cas9 gene-editing approaches. Drought resistance dramatically increased in Slald1 mutants compared with wild-type, which was associated with increased CO2 assimilation, photosystems activities, antioxidant enzymes activities, ascorbate and glutathione content, and reduced reactive oxygen species accumulation, lipid peroxidation and protein oxidation. On the contrary, Slfmo1 mutants were more sensitive to drought, showing damaged photosystems and impaired antioxidant systems, which were significantly alleviated by exogenous ascorbate. Our results demonstrate that Pip biosynthesis and hydroxylated modification pathways play a critical role in drought tolerance through the antioxidant system in tomato. This knowledge can be helpful to breed improved crop cultivars that are better equipped with drought resistance.

Plant glutamate-like receptor genes (GLRs) are homologous to mammalian ionotropic glutamate receptors genes (iGluRs). Although GLRs have been implicated in plant defenses to biotic stress, the relationship between GLR-mediated plant immunity against fungal pathogens and electrical signals remains poorly understood. Here, we found that pretreatment with a GLR inhibitor, 6,7-dinitriquinoxaline-2,3-dione (DNQX), increased the susceptibility of tomato plants to the necrotrophic fungal pathogen Botrytis cinerea. Assessment of the glr3.3, glr3.5 and glr3.3/glr3.5 double-mutants upon B. cinerea infection showed that tomato GLR3.3 and GLR3.5 are essential for plant immunity against B. cinerea, wherein GLR3.3 plays the main role. Analysis of the membrane potential changes induced by glutamate (Glu) or glycine (Gly) revealed that amplitude was significantly reduced by knocking out GLR3.3 in tomato. While treatment with Glu or Gly significantly increased immunity against B. cinerea in wild-type plants, this effect was significantly attenuated in glr3.3 mutants. Thus, our data demonstrate that GLR3.3- and GLR3.5-mediated plant immunity against B. cinerea is associated with electrical signals in tomato plants.

With global climate change, plants are frequently being exposed to various stresses, such as pathogen attack, drought, and extreme temperatures. Transcription factors (TFs) play crucial roles in numerous plant biological processes; however, the functions of many tomato (Solanum lycopersicum L.) TFs that regulate plant responses to multiple stresses are largely unknown. Here, using an RNA-seq approach, we identified SlNAP1, a NAC TF-encoding gene, which was strongly induced by various stresses. By generating SlNAP1 transgenic lines and evaluating their responses to biotic and abiotic stresses in tomato, we found that SlNAP1-overexpressing plants showed significantly enhanced defense against two widespread bacterial diseases, leaf speck disease, caused by Pseudomonas syringae pv. tomato (Pst) DC3000, and root-borne bacterial wilt disease, caused by Ralstonia solanacearum. In addition, SlNAP1 overexpression dramatically improved drought tolerance in tomato. Although the SlNAP1-overexpressing plants were shorter than the wild-type plants during the early vegetative stage, eventually, their fruit yield increased by 10.7%. Analysis of different hormone contents revealed a reduced level of physiologically active gibberellins (GAs) and an increased level of salicylic acid (SA) and abscisic acid (ABA) in the SlNAP1-overexpressing plants. Moreover, EMSAs and ChIP-qPCR assays showed that SlNAP1 directly activated the transcription of multiple genes involved in GA deactivation and both SA and ABA biosynthesis. Our findings reveal that SlNAP1 is a positive regulator of the tomato defense response against multiple stresses and thus may be a potential breeding target for improving crop yield and stress resistance.

Inflammatory bowel disease (IBD) has long been a worldwide health care problem with a persistently increasing incidence. Although its clinical features have been well described, its etiology and pathogenesis remain unclear. IL-16 is a chemoattractant cytokine with various effects on cellular activities and diseases. However, the involvement of IL-16 in IBD remains poorly understood. In this study, to our knowledge we report for the first time the mechanism by which IL-16 induces intestinal inflammation by upregulating the expression of oligopeptide transporter member 1 (PepT1) in a Tetraodon nigroviridis fish model. The dextran sodium sulfate-induced colitis model in this species revealed that IL-16 levels significantly increase accompanied by elevations in PepT1 in the colon. Moreover, the signs of colitis were dramatically attenuated by IL-16 depletion using anti-IL-16 Abs. In vivo IL-16 administration induced remarkable intestinal inflammation with typical ulcerative colitis-like features, including histologic damage, inflammatory cell infiltration, increased myeloperoxidase activity, and proinflammatory cytokines expression, which corresponded with significant PepT1 upregulation in the colon. The IL-16-induced PepT1 expression and its upregulated fMLF transport were also demonstrated in vitro. To our knowledge, our study provides the first evidence of the connection between IL-16 and PepT1, which provides new insights into the molecular mechanism underlying IBD development. Additionally, this study suggests that fish species are an attractive model for studying IBD. By providing a better understanding of IL-16 biology from fish to mammals, this study should aid the development of IL-16-based therapies for IBD.

Three ethylene biosynthesis related genes, EjACS1, EjACO1, and EjACO2, were cloned from the non-climacteric loquat fruit (Eriobotrya japonica Lindl. cv. Luoyangqing). Real-time quantitative PCR (Q-PCR) analysis showed the specific expression of the EjACS1 and EjACO1 genes in fruit, whereas EjACO2 was also expressed in leaves and petals. The expression pattern of EjACO2 was consistent with ethylene production during fruit development, which reached a peak when the fruit color was turning. EjACS1, EjACO1, and EjACO2 all showed low transcript levels throughout 20°C storage in the postharvest ripening loquat. This is the first time that the expression of ethylene biosynthesis related genes has been studied in loquat fruit. Climacteric increases in ethylene production and respiration rate were observed during the development of loquat fruit, and EjACO2 may play an important role in this process.

Ethylene production in non-climacteric fruit is far lower than that of climacteric fruit,which led to the previous conclusion that ethylene played very limited role in regulating ripening and senescence of non-climacteric fruit since 1970s.However,due to the economical importance of many non-climacteric fruit such as citrus,strawberry,grape,loquat,etc,more research work have been reported for such fruit recently.Evident results show that many ripening related processes in non-climacteric fruit are also ethylene regulated,and non-climacteric fruit and climacteric fruit share some similar molecular regulation mechanisms during the changes of fruit quality.Research advance in regulation of ethylene during ripening and senescence of non-climacteric fruit are reviewed in this paper.

ROP/RAC GTPases regulate various development processes and play important roles in plant defense responses. Recently, lignification or secondary cell wall formation related ROP members were reported in rice, zinnia, cotton and Eucalyptus. The present study aimed to investigate the possible association of loquat ROPs with flesh lignification under different temperatures. Four ROP cDNA fragments, EjROP1.1, EjROP1.2, EjROP2 and EjROP3, were isolated from ‘Luoyangqing’ (LYQ) loquat fruit, and all of them shared over 80% nucleotide identity with known ROPs from other plants. Sequence analysis revealed that EjROP1.1, EjROP2 and EjROP3 might be functional while EjROP1.2, with mutated C-terminal resulted from a 65bp deletion in the corresponding nucleotide sequence as compared with EjROP1.1, might be dominant-negative and consequently act as a negative regulator of ROP signal transduction. Increase in expression of EjROP1.1, EjROP2 and EjROP3 was observed during first 4 or 6d of storage at 20°C and was positively correlated with the increase in flesh firmness. Expression of EjROP1.2 was constantly low under 20°C but was quickly, within 6h, induced under 0°C, and it increased by about 20 times within 24h. The expression was induced under 5°C as well but not so strong as that under 0°C, and transfer of fruit from 5°C to 0°C re-stimulated the expression. The possible roles of EjROPs played during senescence and cold regulated lignification was discussed, and the simultaneous increase in the expression of three functional EjROPs and the negative regulator EjROP1.2 was suggested to be important for maintaining a ROP rheostat to protect cells from excessive lignification. To our knowledge, this is the first study on a dominant-negative ROP resulted from a deletion mutation, and a ROP responded to low temperature.

Four expansin cDNA fragments, EjEXPA1, EjEXPA2, EjEXPA3 and EjEXPA4, were isolated and characterized from loquat (Eriobotrya japonica Lindl.) fruit. EjEXPA1 mRNA accumulated consistently with the increase in fruit firmness in 0°C storage of ‘Luoyangqing’ (LYQ) fruit, where chilling injury with increased fruit firmness due to lignification was observed. EjEXPA1 mRNA levels were lower in fruit that underwent low temperature conditioning (LTC, 6d at 5°C then 4d at 0°C), and in 1-methylcyclopropene (1-MCP) treated fruit, in both cases where chilling injury was alleviated. Fruit of the ‘Baisha’ (BS) cultivar soften after harvest rather than increase in firmness, and high expression levels of EjEXPA1 and EjEXPA4 accompanied the softening of BS fruit stored at 20°C; such mRNA accumulation was much lower when fruit were stored at 0°C, where softening was significantly inhibited by the low temperature. Very low expression of EjEXPA2 and EjEXPA3 was observed during storage of both LYQ and BS fruit under the different storage conditions. Our results showed that of the four genes characterized, EjEXPA1 might be associated with chilling-induced lignification while both EjEXPA1 and EjEXPA4 were closely related to softening of loquat fruit during the postharvest period.

Effects of high concentration manganese on active oxygen production and antioxidant enzymes in cucumber leaves under natural irradiation and 1/2 natural irradiation were studied. High concentration manganese increased the H2O2 content and O2*- producing rate of cucumber leaves (Fig.1A, B) and caused lipid peroxidation (Fig.1C). Compare to natural irradiation, 1/2 natural irradiation significantly decreased active oxygen production and lipid peroxidation (Fig.1). CAT activities in cytosols and chloroplasts were inhibited by high concentration manganese (Fig.2B), and other antioxidant enzyme activities were enhanced by high concentration manganese (Fig.2A, C-F). Especially activities of APX, DHAR and GR in chloroplasts were greatly stimulated by high concentration manganese under natural irradiation compared to 1/2 irradiation, which may play important roles in scavenging active oxygen species. Antioxidant enzymes in mitochondria showed higher activities under high concentration manganese under natural irradiation, but the differences were not significant under 1/2 natural irradiation (Fig.2A, C-F).