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Citrus fruits: The proteins of elaioplasts A study of the proteins in bodies called elaioplasts in citrus fruit cells will help to clarify elaioplast formation and functions. Plant cells contain several types of membrane-bound bodies called plastids, with elaioplasts being an incompletely characterized type. They are known to store oils in the cells, especially molecules called terpenes that influence the fragrances and flavors of citrus fruits. Researchers in China, led by Yunliu Zeng at Huazhong Agricultural University, analyzed the protein molecules in elaioplasts of kumquat peel to investigate possible roles for elaioplasts other than oil storage. They identified more than 600 proteins and assigned likely functions to many. The results suggest the proteins are involved in chemical energy transactions and the manufacture of various categories of biomolecules. This will guide research to fully characterize the activities and significance of elaioplasts.

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.

● Fortunella genus consists of two populations: cultivated kumquat and wild Hong Kong kumquat. ● Artificial selection might involve in the origin of cultivated Fortunella species. ● A hypothesis for the differentiation and speciation of Fortunella species is proposed. Kumquat (Fortunella spp.) is a fruit and ornamental crop worldwide due to the palatable taste and high ornamental value of its fruit. Although Fortunella is classified into the economically important true citrus fruit tree group together with Citrus and Poncirus, few studies have been focused on its evolutionary scenario. In this study, analysis of five chloroplast loci and 47 nuclear microsatellites (nSSR) loci from 38 kumquat and 10 citrus accessions revealed the independent phylogeny of Fortunella among citrus taxa, and that Fortunella mainly comprises two populations: CUL, cultivated Fortunella spp. (F. margarita, F. crassifolia and F. japonica); and HK, wild Hong Kong kumquat (Fortunella hindsii). Genomic analysis based on whole-genome SNPs indicated that the allele frequency of both pupations deviated from the neutral selection model, suggesting directional selection was a force driving their evolutions. CUL exhibited lower genomic diversity and higher linkage strength than HK, suggesting artificial selection involved in its origin. A high level of genetic differentiation (Fst = 0.364) was detected and obviously asynchronous demographic changes were observed between CUL and HK. Based on these results, a new hypothesis for the speciation of Fortunella is proposed.

[Objectives] This study was conducted to develop a rapid identification method for citrus germline materials resistant to Huanglongbing disease and lay a basis for accelerating citrus breeding for resistance to Huanglongbing and increasing the breeding efficiency. [Methods] Thirty-six citrus germplasms suspected to be resistant to citrus Huanglongbing disease were collected. The method of direct high grafting to citrus trees infected with Huanglongbing pathogen was adopted. The resistance of the test materials was identified and evaluated by field symptoms combined with quantitative PCR. It was defined as the top grafting identification method. [Results] The test materials that were grafted in spring started to germinate after one month, and three months late (June 5, 2018) typical mottled yellowing on leaves was observed on KH-14 for the first time. After four months ( July 5, 2018) of top grafting, typical mottled yellowing occurred on 23 materials, and 11 materials showed no such symptom. After six months (September 4, 2018) of top grafting, although the growth of KH-18, KH-12, KHY-4, KHY-5 and KHY-6 were normal, yellowing was observed on their leaves. Only KH-21 grew well, and showed no yellow shoots and yellowing leaves. It was identified as the material with resistance to Huanglongbing disease. Quantitative PCR tests on the above six materials showed that KH-21 was negative and other five were positive. Real-time fluorescence quantitative PCR test indicated that the average Huanglongbing bacteria amount in KH-21 was 1 870.0 cell/[xg DNA, and the average Huanglongbing bacteria amount in the control material was 372 285. 5 cell/[xg DNA, indicating KH-21 was resistant to Huanglongbing bacteria. [ Conclusions] The method for infecting bacteria by top grafting takes six months, can detect large amount of seedlings, and is time-saving, efficient, cost-saving and accurate. This method can quickly identify the resistance of citrus varieties to citrus Huanglongbing disease, and can be popularized and used in the identification of citrus Huanglongbing disease resistance. [ABSTRACT FROM AUTHOR]

Huanglongbing (HLB) is one of the most destructive diseases in citrus production worldwide. Early detection of HLB pathogens can facilitate timely removal of infected citrus trees in the field. However, low titer and uneven distribution of HLB pathogens in host plants make reliable detection challenging. Therefore, the development of effective detection methods with high sensitivity is imperative. This study reports the development of a novel method, tandem repeat-based polymerase chain displacement reaction (TR-PCDR), for the detection of 'Candidatus Liberibacter asiaticus', a widely distributed HLB-associated bacterium. A uniquely designed primer set (TR2-PCDR-F/ TR2-PCDR-1R) and a thermostable Taq DNA polymerase mutant with strand displacement activity were used for TR-PCDR amplification. Performed in a regular thermal cycler, TR-PCDR could produce more than two amplicons after each amplification cycle. Sensitivity of the developed TR-PCDR was 10 copies of target DNA fragment. The sensitive level was proven to be lOOx higher than conventional PCR and similar to real-time PCR. Data front the detection of 'Ca. L. asiaticus' with filed samples using the above three methods also showed similar results. No false-positive TR-PCDR amplification was observed from healthy citrus samples and water controls. These results thereby illustrated that the developed TR-PCDR method can be applied to the reliable, highly sensitive, and cost-effective detection of 'Ca. L. asiaticus'. [ABSTRACT FROM AUTHOR]