Differential expression of microRNAs in response to Papaya ringspot virus infection in differentially responding genotypes of papaya (Carica papaya L.) and its wild relative

Papaya ringspot virus (PRSV) is one of the most devastating viruses of papaya that has significantly hampered papaya production across the globe. Although PRSV resistance is known in some of its wild relatives, such as Vasconcellea cauliflora and in some of the improved papaya genotypes, the molecular basis of this resistance mechanism has not been studied and understood. Plant microRNAs are an important class of small RNAs that regulate the gene expression in several plant species against the invading plant pathogens. These miRNAs are known to manifest the expression of genes involved in resistance against plant pathogens, through modulation of the plant’s biochemistry and physiology. In this study we made an attempt to study the overall expression pattern of small RNAs and more specifically the miRNAs in different papaya genotypes from India, that exhibit varying levels of tolerance or resistance to PRSV. Our study found that the expression of some of the miRNAs was differentially regulated in these papaya genotypes and they had entirely different miRNA expression profile in healthy and PRSV infected symptomatic plants. This data may help in improvement of papaya cultivars for resistance against PRSV through new breeding initiatives or biotechnological approaches such as genome editing

Viral Diseases of Banana and their Management

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(European Journal of Plant Pathology,110:871-882)The ability of Papaya ringspot virus strains overcoming the transgenic resistance of papaya conferred by the coat protein gene is not correlated with higher degrees of sequence divergence from the transgene

The coat protein (CP) gene mediated transgenic resistance is found to be the best approach for protecting papaya plants against the destructive disease caused by Papaya ringspot viruses (PRSV). In order to study the variability of PRSV and the potential threat to the CP-transgenic resistance, five virus isolates were collected from transgenic plants of papaya line 16-0-1, which carry the CP gene of the typical mosaic strain of Taiwan PRSV YK, in an approved test field and fourteen from untransformed papaya plants in different areas of Taiwan. The results of biological, serological, and molecular characterization indicated that all isolates are related to PRSV YK. Among them, the isolate 5-19 from the transgenic line and the isolates CS and TD2 from untransformed papaya were able to overcome the YK CP gene-mediated resistance of papaya lines 18-2-4, 17-0-5, and 16-0-1, which provide high degrees of resistance to different geographic PRSV strains of Hawaii (HA), Mexico (MX), and Thailand (TH). These three isolates were also able to cause symptoms on untransformed papaya plants more severe than those induced by YK. In addition to the host reactions, the variability of the collected 19 isolates was also analyzed and compared with YK and other geographic strains by heteroduplex mobility assay (HMA) and sequence analyses. The results of HMA indicated that the CP genes of isolates 5-19 and TD2 are more divergent than those of other isolates when compared with YK. However, sequence analyses of the transgenic-resistance overcoming isolates 5-19, CS, and TD2 revealed that their CP coding regions and the 3' untranslated regions (UTRs) share nucleotide identities of 93.9-96.6% and 94.2-97.9% with those of YK, respectively; whereas the other geographic strains of HA, MX, and TH that could not overcome the transgenic resistance share lower nucleotide identities of 89.8-92.6% and 92.3-95.3% with those of YK, respectively. Our results indicate that the ability for overcoming the transgenic resistance is not solely correlated with higher degrees of sequence divergence from the transgene. The possible mechanism for overcoming the transgenic resistance and the potential threat of these PRSV strains to the application of the transgenic papaya lines carrying PRSV YK CP gene are discussed

Tomato Spotted Wilt

This article describes the symptoms and spread of tomato spotted wilt, management techniques, and the future of biotechnology in the fight against tomato spotted wilt

Characterization of Insertion Sites in Rainbow Papaya, the First Commercialized Transgenic Fruit Crop

Inserts and insert sites in transgenic, papaya ringspot virus (PRSV)-resistant commercial papaya Rainbow and SunUp, were characterized as part of a petition to Japan to allow import of fresh fruit of these cultivars from the U.S. and to provide data for a larger study aimed at understanding the global impact of DNA transformation on whole genome structure. The number and types of inserts were determined by Southern analysis using probes spanning the entire transformation plasmid and their sequences determined from corresponding clones or sequence reads from the whole-genome shotgun (WGS) sequence of SunUp papaya. All the functional transgenes, coding for the PRSV coat protein (CP), neophosphotransferase (nptII) and β-glucuronidase (uidA) were found in a single 9,789 basepair (bp) insert. Only two other inserts, one consisting of a 290 bp nonfunctional fragment of the nptII gene and a 1,533 bp plasmid-derived fragment containing a nonfunctional 222 bp segment of the tetA gene were detected in Rainbow and SunUp. Detection of the same three inserts in samples representing transgenic generations five to eight (R5 to R8) suggests that the three inserts are stably inherited. Five out of the six genomic DNA segments flanking the three inserts were nuclear plastid sequences (nupts). From the biosafety standpoint, no changes to endogenous gene function based on sequence structure of the transformation plasmid DNA insertion sites could be determined and no allergenic or toxic proteins were predicted from analysis of the insertion site and flanking genomic DNA