‘Zhique’ (Citrus wilsonii Tanaka) is a traditional Chinese medicine. Its fruits have been used to treat inflammation-related symptoms, such as cough and sputum, though the underlying mechanism remains poorly understood. The aim of this study was to investigate the anti-inflammatory properties of ‘Zhique’ pulp extract (ZQE) in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages and primary mouse bone marrow-derived dendritic cells (BMDCs). The flavonoid profiles of the ZQE were determined by high performance liquid chromatography. The anti-inflammatory activity was evaluated in LPS-induced inflammatory RAW 264.7 macrophages and BMDCs through enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and Western blot assays. Naringin was a predominant flavonoid occurring in ZQE, followed by eriocitrin, hesperidin, neohesperidin, rhoifolin, naringenin, and poncirin. ZQE exhibited a very low cytotoxicity in LPS-stimulated RAW 264.7 macrophages. Meanwhile, ZQE significantly inhibited the production of prostaglandins E2 and secretion of cyclooxygenase-2 protein in LPS-stimulated RAW 264.7 macrophages, and markedly suppressed the mRNA expression of inflammatory mediators, such as cyclooxygenase-2, tumor necrosis factor alpha, interleukin-1 beta (IL-1β), and IL-6 in LPS-induced RAW 264.7 macrophages and/or primary BMDCs. The ZQE inhibited the inflammatory responses in RAW 264.7 macrophages and BMDCs triggered by LPS. The results suggested that ‘Zhique’ has a high potential as a novel therapeutic agent to treat chronic inflammatory diseases.

Lanelate navel orange (Citrus sinensis Osbeck) is a late-ripening citrus cultivar increasingly planted in China. The physiological disorder juice sac granulation often occurs in the fruit before harvest, but the physiological and molecular mechanisms underlying this disorder remain elusive. In this study, we found that fruit granulation of the late-ripening navel orange in the Three Gorges area is mainly caused by the low winter temperature in high altitude areas. Besides, dynamic changes of water content in the fruit after freezing were clarified. The granulation of fruit juice sacs resulted in increases in cell wall cellulose and decreases in soluble solid content, and the cells gradually became shrivelled and hollow. Meanwhile, the contents of pectin, cellulose, and lignin in juice sac increased with increasing degrees of fruit granulation. The activities of pectin methylesterase (PME) and the antioxidant enzymes peroxidase (POD), superoxide dismutase, and catalase increased, while those of polygalacturonase (PG) and cellulose (CL) decreased. Furthermore, a total of 903 differentially expressed genes were identified in the granulated fruit as compared with non-disordered fruit using RNA-sequencing, most of which were enriched in nine metabolic pathways, and qRT-PCR results suggested that the juice sac granulation is closely related to cell wall metabolism. In addition, the expression of PME involved in pectin decomposition was up-regulated, while that of PG was down-regulated. Phenylalanine ammonia lyase (PAL), cinnamol dehydrogenase (CAD), and POD related to lignin synthesis were up-regulated, while CL involved in cellulose decomposition was down-regulated. The expression patterns of these genes were in line with those observed in low-temperature treatment as revealed by qRT-PCR, further confirming that low winter temperature is associated with the fruit granulation of late-ripening citrus. Accordingly, low temperature would aggravate the granulation by affecting cell wall metabolism of late-ripening citrus fruit.

Field observations indicate that boron (B)‐toxicity symptoms may occur in citrus plants from inappropriate foliar spraying or overfertilizing with B especially under low‐rainfall conditions, where B can accumulate to levels that become toxic to plant growth. Previous work has indicated that different rootstocks can greatly influence the scion's tolerance to B toxicity, however, little is known about the response of different citrus scion–rootstock combinations to excess‐B conditions. In the present study, we investigated the effects of excess B on plant growth, gas exchange, B concentration, and distribution of four scion–rootstock combinations, Newhall and Skagg's Bonanza navel orange (Citrus sinensis Osb.) scions grafted on Carrizo citrange (C. sinensis L. Osb. × Poncirus trifoliata L. Raf.) and Trifoliate orange (Poncirus trifoliata L. Raf.) rootstocks. One‐year‐old plants of the four scion–rootstock combinations were grown for 183 d in sand–perlite (1 : 1, v/v) medium under greenhouse conditions. The plants were irrigated with half‐strength Hoagland's nutrient solution containing two B concentrations, 0.25 (control) and 2.50 (excess B) mg L^–1. It was found that, apart from the combination of Newhall grafted on Carrizo citrange, the dry weights in various parts of the other three combinations were reduced by the excess‐B treatment. Furthermore, the plants of Skagg's Bonanza grafted on Carrizo citrange showed the highest growth reduction amongst the four scion–rootstock combinations. In most cases, the greater reductions in dry weight were found in roots as compared to the other plant parts under excess‐B conditions, indicating that roots were more sensitive to B toxicity than the other tissues. In the case of Newhall plants grafted on Carrizo citrange, the entire plant growth was increased by excess‐B treatment. Boron concentrations in all plants parts increased significantly by increasing the B supply in the nutrient solution. Leaves were the dominant sites of B accumulation and showed the greatest increase in B concentration compared to the other plant parts, as B concentration in the nutrient solution increased. Our results indicate that the combination of Newhall grafted on Carrizo citrange was more tolerant to B toxicity, while the combination of Skagg's Bonanza grafted on Carrizo citrange was relatively more sensitive to B toxicity, in comparison with the other scion–rootstock combinations. However, Newhall plants contained more B in leaves and in roots than Skagg's Bonanza plants when they were both grafted on Carrizo citrange, indicating that the mechanism underlying such great differential growth responses of the two scion–rootstock combinations to B toxicity may not be associated with B exclusion from roots or reduced translocation of B to shoots. Furthermore, B distribution in different plant parts implied that the mechanism was also unlikely related to altered distributions of accumulated B in plant tissues. However, inherent ability to tolerate excessive B concentration in plant tissues may be involved in B tolerance.

The plant rhizosphere microbiome is known to play a vital role in plant health by competing with pathogens or inducing plant resistance. This study aims to investigate rhizosphere microorganisms responsive to a devastating citrus disease caused by ‘Candidatus Liberibacter asiaticus’ (CLas) infection, by using 16S rRNA sequencing and metagenome technologies. The results show that 30 rhizosphere and 14 root bacterial genera were significantly affected by CLas infection, including 9 plant resistance-associated bacterial genera. Among these, Amycolatopsis, Sphingopyxis, Chryseobacterium, Flavobacterium, Ralstonia, Stenotrophomonas, Duganella, and Streptacidiphilus were considerably enriched in CLas-infected roots, while Rhizobium was significantly decreased. Metagenome analysis revealed that the abundance of genes involved in carbohydrate metabolism, such as glycolysis, starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, was significantly reduced in the CLas-infected citrus rhizosphere microbial community. Likewise, the abundance of genes involved in phosphoinositide signaling and phosphoinositide metabolism, which play important roles in energy metabolism (such as carbohydrate metabolism and lipid metabolism), was also decreased in the CLas-infected samples. Taken together, our results indicate that CLas infection could affect the resistance potential and energy metabolism of the citrus rhizosphere microbial community, which may help us to understand the rhizosphere responses to plant disease and thus facilitate the development and application of antagonistic microorganism products in citrus industry.