Carotenoid content is the primary determinant of fruit color that affects nutritional value and appearance in tomato. Phytoene synthase (PSY) is the key regulatory enzyme in the carotenoid biosynthesis pathway. Absent function of PSY1 in tomato fruit results in yellow flesh phenotype. We, here, report that two different transcripts, a wild-type (Psy1) and a chimeric mRNA (Psy1/Unknown), exist in a yellow-fruited tomato accession PI 114490. Psy1/Unknown is generated by joining exons from two different genes, Psy1 and an unknown gene, transcribed using both complementary DNA strands. The Psy1 shows low expression in the fruit of PI 114490, while the expression of Psy1/Unknown in the fruit of PI 114490 shows the same pattern as Psy1 in red fruit. The PSY1/Unknown has a lower function than PSY1 in a bacterial expression system. Coincidence of one single-nucleotide polymorphism (SNP) in the fourth intron and one simple sequence repeat (SSR) with 19 AT repeats in the downstream sequence of Psy1 gene with Psy1/Unknown in a set of yellow-fruited tomato lines indicates that Psy1/Unknown might be caused by the SNP and/or SSR. One possible explanation of these observations is trans-splicing. Severely reduced Psy1 transcript caused by Psy1/Unknown results in low accumulation of carotenoid and yellow flesh in PI 114490.

Cucumber green mottle mosaic virus (CGMMV; genus Tobamovirus) infects frequently the grafted watermelon and is widely distributed in China. Investigating the transmission modes and their efficiency is urgently needed to understand the factors contributing to the epidemiology of this viral disease. In the present study, we found that the occurrence of CGMMV in a bottle gourd seed production base reached 100%, while the contamination rate and transmission rate were 100 and 0.92%, respectively. The bottle gourd plants showed obvious mottle symptom on leaves starting 36 days after seed sowing. The long latent period of CGMMV in seedlings implies a potential risk to use contaminated seeds in the production of grafted watermelon. This virus could overwinter in soil with debris of infected plants, and the infection rate of CGMMV from contaminated soils was 10.30%. CGMMV could be transmitted from infected watermelon plants to healthy ones by pruning at least to the ninth plant during the whole growing season. The transmission distance was 1.87 m by drip irrigation and 2.31 m by flow irrigation. This study suggested that contaminated seeds, contaminated soil, pruning and irrigation could transmit CGMMV at different efficiency, and all contribute to the epidemiology of CGMMV.

Cucurbit chlorotic yellows virus (CCYV) (genus Crinivirus, family Closteroviridae) is an emerging plant virus, and is now spreading and causing severe economic losses to cucurbit crops in many Asian countries. CCYV is believed to be transmitted specifically by the sweetpotato whitefly, Bemisia tabaci, in a semipersistent manner. In the present study, we provide direct evidence for the semipersistent transmission of CCYV by Mediterranean (MED) cryptic species of B. tabaci complex. We investigated CCYV transmission characteristics, and immunofluorescently labeled and localized the virus retention site within the vector by laser confocal microscopy. Whiteflies required ≥1 h of acquisition access period (AAP) to successfully acquire CCYV, and the proportion of RT-PCR positive whitefly individuals reached to 100% at 48 h of AAP. CCYV virons could be retained within vectors as long as 12 d, but the proportion of RT-PCR positive whiteflies dropped to 55% by 3 d. Groups of thirty whiteflies given a 24 h of inoculation access period (IAP) to inoculate CCYV on cucumber plants showed a transmission efficiency rate of 72.73%. The retention site of CCYV virons was located in the foregut of virion-fed vectors. These results definitely indicated the semipersistent transmission mode of CCYV by B. tabaci MED.

It is known that plant viruses can change the performance of their vectors. However, there have been no reports on whether or how a semipersistent plant virus manipulates the feeding behaviors of its whitefly vectors. Cucurbit chlorotic yellows virus (CCYV) (genus Crinivirus, family Closteroviridae) is an emergent plant virus in many Asian countries and is transmitted specifically by B and Q biotypes of tobacco whitefly, Bemisia tabaci (Gennadius), in a semipersistent manner. In the present study, we used electrical penetration graph (EPG) technique to investigate the effect of CCYV on the feeding behaviors of B. tabaci. The results showed that CCYV altered feeding behaviors of both biotypes and sexes of B. tabaci with different degrees. CCYV had stronger effects on feeding behaviors of Q biotype than those of B biotype, by increasing duration of phloem salivation and sap ingestion, and could differentially manipulate feeding behaviors of males and females in both biotype whiteflies, with more phloem ingestion in Q biotype males and more non-phloem probing in B biotype males than their respective females. With regard to feeding behaviors related to virus transmission, these results indicated that, when carrying CCYV, B. tabaci Q biotype plays more roles than B biotype, and males make greater contribution than females.

Background: Cucurbits produce fruits or vegetables that have great dietary importance and economic significance worldwide. The published genomes of at least 11 cucurbit species are boosting gene mining and novel breeding strategies, however genetic transformation in cucurbits is impractical as a tool for gene function validation due to low transformation efficiency. Virus-induced gene silencing (VIGS) is a potential alternative tool. So far, very few ideal VIGS vectors are available for cucurbits. Results: Here, we describe a new VIGS vector derived from cucumber green mottle mosaic virus (CGMMV), a monopartite virus that infects cucurbits naturally. We show that the CGMMV vector is competent to induce efficient silencing of the phytoene desaturase (PDS) gene in the model plant Nicotiana benthamiana and in cucurbits, including watermelon, melon, cucumber and bottle gourd. Infection with the CGMMV vector harboring PDS sequences of 69-300 bp in length in the form of sense-oriented or hairpin cDNAs resulted in photobleaching phenotypes in N. benthamiana and cucurbits by PDS silencing. Additional results reflect that silencing of the PDS gene could persist for over two months and the silencing effect of CGMMV-based vectors could be passaged. Conclusions: These results demonstrate that CGMMV vector could serve as a powerful and easy-to-use tool for characterizing gene function, controlling viral pathogens or even performing resistance breeding in cucurbits. Moreover, this study will possess considerable important reference value for developing different viral vectors.

Systemic foliar chlorosis of melon, watermelon, and cucumber plants grown in plastichouses was first observed in Shanghai, China in 2008. By the end of October 2009, this symptom had become prevalent across 13,000 ha of plastichouses in Shanghai, Ningbo in Zhejiang Province, and Shouguang in Shandong Province. By mid-October, disease incidence ranged from 50 to 100% and losses were estimated between 10 and 20% across 100 plastichouses. Initial disease symptoms were chlorosis beginning at the base and middle portion of the older leaves followed by development of chlorotic spots on the lamina. Within 4 to 5 days, the entire leaf lamina was bright yellow and the veins remained green. The whitefly, Bemisia tabaci, was frequently observed colonizing plants in all plastichouses included in this study. Leaf samples were collected from six symptomatic cucumber, melon, and watermelon plants from individual plastichouses in Shanghai, Ningbo, and Shouguang. A pair of degenerate primers, F-5′-GGN TTA GAN TTC GGN ACN AC-3′ and R-5′-TCA AAN GTN CCN CCN CCN AA-3′, that were specific for the genera Crinivirus and Closterovirus, family Closteroviridae (2) were used to amplify a 636-bp fragment of the viral heat shock protein 70 gene (Hsp70). A PCR product of the expected size was amplified from RNA extracted with TaKaRa RNAiso Reagent (TaKaRa, Dalian, China) from symptomatic leaf samples: 3 of 3 melon, 2 of 2 watermelon, and 1 of 1 cucumber, and from 5 of 5 Bemisia tabaci adults collected from plants in five plastichouses in Shanghai, Ningbo, and Shouguang. No PCR product was obtained from RNA extracted from cucumber leaves grown in a virus-free facility at the Fruit Research Institute, Zhengzhou. PCR products were sequenced from representative plants samples and the sequences were submitted to GenBank (Nos. GU721105 to GU721107, GU72118 to GU721110, and GU721111. The six Hsp70 sequences shared 99.8 to 100% identity with Cucurbit chlorotic yellows virus (CCYV) (GenBank No. AB523789) from Japan. Using the complete CCYV sequence (1), PCR primers were designed to amplify the complete CCYV coat protein (Cp): Cp F-5′-CGCAATCAATAAGGCGGCGACC-3′ and Cp R-5′-ACTACAACCTCCCGGTGCCAACT-3′ (804 bp), minor Cp (Cpm): Cpm-F-5′-TGATGAANTGCCANGCTNTGAAA-3′ and Cpm-R5′-ACAANTGATTCACATTNACAAT-3′ (1,632 bp); and Hsp70: Hsp F-5′-TGCAACCGATGTCAGGTTCAGCG-3′ with Hsp R-5′-TGGATAATTGGTCACGACCTCCAGT-3′ (1,947 bp). One PCR amplicon was obtained for each target gene using RNA extracted from a cucumber collected in Ningbo. Three of the PCR amplicons were cloned and the DNA sequence was determined. A representative sequence for each gene was deposited in GenBank as: cp (HM581658), cpm (HM581657), and hsp70 (HM581659). The cp, cpm, and hsp70 sequences shared 99.7, 99.9, and 99.9% nt identity with the respective genes of CCYV (AB523789), whereas they shared only 62.5, 49.9, and 69.6% identity with the respective gene sequences for Cucurbit yellow stunting disorder virus (CYSDV; NC004810), suggesting the two viruses are divergent crinivirus species. Although this virus was first reported to infect cucurbits in Japan in 2009 (1), to our knowledge, this is the first report of CCYV in China. Eradication and management efforts are therefore paramount to reducing the spread of the disease. References: (1) M. Okuda et al. Phytopathology 100:560, 2010. (2) T. Tian et al. Phytopathology 86:1167, 1996.

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Background: Plant viruses can affect vector's behaviors in order to enhance viral transmission. Cucurbit chlorotic yellows virus (CCYV) (genus Crinivirus) is an emergent RNA plant virus and is transmitted specifically by biotypes B and Q of tobacco whitefly, Bemisia tabaci (Gennadius), in a semipersistent manner. Methods: We used the electrical penetration graph (EPG) to investigate the effect of CCYV on the feeding behaviors of B. tabaci biotypes B and Q. Results: CCYV could affect, both directly and indirectly, the feeding behaviors of B. tabaci to various degrees, depending on biotypes and sexes of the insect. CCYV showed stronger direct effects on biotype Q than on biotype B in terms of increased non-phloem probing and phloem salivation. CCYV increased non-phloem probing and phloem salivation more on females than on males of biotype Q, and increased phloem salivation more on females than on males of biotype B. CCYV had stronger indirect effects, via virus-infested plants, on biotype B than on biotype Q by enhancing phloem sap ingestion and feeding bouts. CCYV increased non-phloem probing and feeding bouts more on males than on females of biotype B, and decreased phloem sap ingestion more on males than on females on biotype Q indirectly. Conclusions: The results clearly indicated that CCYV affects the feeding behaviors of B. tabaci, which may lead to increased ability of the B. tabaci for CCYV transmission.