Project description:With the aid of a biochip, carrying representative sequences from approximately 2200 sequences from the genome of isolate 9a5c from X. fastidiosa (Xf), microarray-based comparisons have been performed with 6 different Xf isolates obtained from citrus plants (Table 1). Four of these isolates (56a, 9.12c, 187b, and 36f) were obtained from CVC-affected trees and are representatives of the most prevalent Xf haplotypes found in sweet orange orchards across the state of São Paulo, while isolate CV21 was obtained from a non-symptomatic tree from the same region. Isolate Fb7, on the other hand, was obtained from a sweet orange tree that displayed symptoms of “Pecosita”, a disease similar to CVC that occurs in some citrus-growing regions of Argentina. Keywords: Comparative Genomic Hybridization
Project description:Huanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. A powerful oligonucleotide microarray of high-density 16S rRNA genes, the PhyloChip microarray, has been developed and effectively used to study bacterial diversity, especially from environmental samples. In this article, we aim to decipher the bacterial microbiome in HLB-affected citrus versus non-infected citrus as well as in citrus plants treated with ampicillin and gentamicin using PhyloChip-based metagenomics.
Project description:Candidatus Liberibacter asiaticus (Las), a non-culturable phloem-limited bacterium, is the suspected causal agent of Huanglongbing (HLB) in Florida. HLB is one of the most devastating diseases of citrus and no resistant cultivars have been identified to date, though tolerance has been suggested in the genus Poncirus. A recent study conducted in our laboratory demonstrated tolerance of US-897, a hybrid of Poncirus trifoliata (L. Raf.) and the susceptible ‘Cleopatra’ mandarin (Citrus reticulata Blanco), to Ca. L. asiaticus, the presumed causal agent of HLB in Florida (Albrecht & Bowman, HortScience 46 (2011) 16-22). This study compares transcriptional changes in tolerant US-897 and susceptible ‘Cleopatra’ mandarin seedlings in response to infection with Las using the Affymetrix GeneChip citrus array with the main objective of identifying genes associated with tolerance to HLB. Such genes may be suitable as potential targets for biotechnology approaches, providing one strategy to possibly control this destructive disease of citrus. Fifteen months-old seedlings of the genotypes 'Cleopatra' mandarin and US-897 were graft-inoculated with non-infected (control) or Las-infected tissue from greenhouse-grown 'Valencia' (C. sinensis L.) plants. Six non-infected control plants each from 'Cleopatra' (MC) and US-897 (TC) and six infected plants each from Cleopatra (MI) and US-897 (TI) were used. Four to six leaves per plant were excised at 32 weeks after inoculation (wai) and immediately frozen in liquid nitrogen. Total RNA was extracted from all 24 plants. Equal amounts of RNA from two samples were pooled to obtain three biological replicates per genotype and treatment and used for hybridization on Affymetrix citrus microarrays.
Project description:Somatic embryogenesis in nucellar tissues is widely recognized to induce polyembryony in major citrus varieties such as sweet oranges, satsuma mandarins and lemons. This capability for apomixis is attractive in agricultural production systems using hybrid seeds, and many studies have been performed to elucidate the molecular mechanisms of various types of apomixis. To identify the gene responsible for somatic embryogenesis in citrus, a custom oligo-DNA microarray including predicted genes in the citrus polyembryonic locus was used to compare the expression profiles in reproductive tissues between monoembryonic and polyembryonic varieties. The full length of CitRKD1, which was identified as a candidate gene responsible for citrus somatic embryogenesis, was isolated from satsuma mandarin and its molecular function was investigated using transgenic ‘Hamlin’ sweet orange by antisense-overexpression. The candidate gene CitRKD1, predominantly transcribed in reproductive tissues of polyembryonic varieties, is a member of the plant RWP-RK domain proteins. CitRKD1 of satsuma mandarin comprised two alleles (CitRKD1-mg1 and CitRKD1-mg2) at the polyembryonic locus controlling embryony type (mono/polyembryony) that were structurally divided into two types with or without a miniature inverted-repeat transposable element (MITE)-like insertion in the upstream region. CitRKD1-mg2 with the MITE insertion was the predominant transcript in flowers and young fruits where somatic embryogenesis of nucellar cells occurred. Loss of CitRKD1 function by antisense-overexpression abolished somatic embryogenesis in transgenic sweet orange and the transgenic T1 plants were confirmed to derive from zygotic embryos produced by self-pollination by DNA diagnosis. Genotyping PCR analysis of 95 citrus traditional and breeding varieties revealed that the CitRKD1 allele with the MITE insertion (polyembryonic allele) was dominant and major citrus varieties with the polyembryonic allele produced polyembryonic seeds.
Project description:Background: MicroRNAs play important roles in the adaptive responses of plants to nutrient deficiencies. Here, we sequenced two small RNA libraries from B-deficient and -sufficient (control) Citrus sinensis leaves, respectively, using Illumina sequencing in order to identify the potential miRNAs related to the tolerance of citrus to B-deficiency. Results: Ninety one (83 known and 8 novel) up- and 81 (75 known and 6 novel) downregulated miRNAs were isolated from B-deficient leaves. The great alteration of miRNA expression might contribute to the tolerance of citrus to B-deficiency. The adaptive responses of miRNAs to B-deficiency might related to several aspects: (a) attenuation of plant growth and development by repressing auxin signaling due to decreased TIR1 level and ARF-mediated gene expression by altering the expression of miR393, miR160 and miR3946; (b) maintaining leaf phenotype and enhancing the stress tolerance by up-regulating NACs targeted by miR159, miR782, miR3946 and miR7539; (c) activation of the stress responses and antioxidant system through down-regulating the expression of miR164, miR6260, miR5929, miR6214, miR3946 and miR3446; (d) decreasing the expression of major facilitator superfamily protein genes targeted by miR5037, thus lowering B export from plants. Also, B-deficiency-induced downregulation of miR408 might play a role in plant tolerance to B-deficiency by regulating Cu homeostasis and enhancing superoxide dismutase activity. Conclusions: Our study reveals some novel responses of citrus to B-deficiency, which increase our understanding of the adaptive mechanisms of citrus to B-deficiency at the miRNA (post-transcriptional) level.