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Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), has emerged since 2008 and is the most important disease of kiwifruit, threatening its production in the world. Until now, little is known about the molecular interaction between Psa and kiwifruit plants: to elucidate early molecular events of kiwifruits-Psa interaction, Illumina RNA-seq was conducted at 3 h, 24 h and 48 h after Psa inoculation and mock inoculation, both on acibenzolar-S-methyl (ASM)-pretreated and untreated Actinidia chinensis plants. De novo assembly of kiwifruit transcriptome consists of 39,607 transcripts, about 4500 of them were differentially expressed (DE) in the various situations. During infection process, genes modulation caused by Psa in A. chinensis involve about 3000 transcripts modulated that is mainly evident at 3hpi rather than 24hpi or 48hpi. Only few transcripts were common between the three infections time points (1,5%). Moreover, transcripts modulation in infected ASM-untreated plants were higher than in ASM pre-treated infected plants. To investigate transcriptome expression profile during infection process, both in ASM untreated and ASM pre-treated plants, Hierarchical Cluster Analysis (HCA) were performed to reveal the coordinates change of some important gene functional categories. Moreover, MapMan has been shown to be an effective tool to map transcriptome data, to define functional categories and to perform time course analysis in order to identify differentially-represented functional groups. Regulation overview highlight difference in hormonal balance, transcriptional regulation and signaling. For example, seven major families of TF (AP2/ERF, MYB, Myc-bHLH, GATA, NAC, WRKY and GRAS), reported as linked to plant stress responses such as pathogens, were found DE in response to Psa in ASM pretreated plants with respect to the untreated ones. Different TFs were linked also with signaling and hormonal balance and probably involved in the ability of ASM plants to assemble the right defense response against PSA. On the other side, ASM untreated plants try to mount a response at 3 hpi , but not adequate to counteract the infection. Moreover, the RNA-seq technology has permitted to identify novel differentially expressed transcripts of unknown functions but related with infection and ASM treatment. Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), has emerged since 2008 and is the most important disease of kiwifruit, threatening its production in the world. Until now, little is known about the molecular interaction between Psa and kiwifruit plants: to elucidate early molecular events of kiwifruits-Psa interaction, Illumina RNA-seq was conducted at 3 h, 24 h and 48 h after Psa inoculation and mock inoculation, both on acibenzolar-S-methyl (ASM)-pretreated and untreated Actinidia chinensis plants. De novo assembly of kiwifruit transcriptome consists of 39,607 transcripts, about 4500 of them were differentially expressed (DE) in the various situations. During infection process, genes modulation caused by Psa in A. chinensis involve about 3000 transcripts modulated that is mainly evident at 3hpi rather than 24hpi or 48hpi. Only few transcripts were common between the three infections time points (1,5%). Moreover, transcripts modulation in infected ASM-untreated plants were higher than in ASM pre-treated infected plants. To investigate transcriptome expression profile during infection process, both in ASM untreated and ASM pre-treated plants, Hierarchical Cluster Analysis (HCA) were performed to reveal the coordinates change of some important gene functional categories. Moreover, MapMan has been shown to be an effective tool to map transcriptome data, to define functional categories and to perform time course analysis in order to identify differentially-represented functional groups. Regulation overview highlight difference in hormonal balance, transcriptional regulation and signaling. For example, seven major families of TF (AP2/ERF, MYB, Myc-bHLH, GATA, NAC, WRKY and GRAS), reported as linked to plant stress responses such as pathogens, were found DE in response to Psa in ASM pretreated plants with respect to the untreated ones. Different TFs were linked also with signaling and hormonal balance and probably involved in the ability of ASM plants to assemble the right defense response against PSA. On the other side, ASM untreated plants try to mount a response at 3 hpi , but not adequate to counteract the infection. Moreover, the RNA-seq technology has permitted to identify novel differentially expressed transcripts of unknown functions but related with infection and ASM treatment.

Pseudomonas syringae pv. actinidiae (Psa),the causative agent of bacterial canker of kiwi, was firstly isolated in 1992, but the second outbreak dating back to 2008 is now in charge of a large pandemic that has led to major economic losses worldwide. Despite the high economic impact of Pseudomonas syringae pv. actinidiae (Psa) on kiwifruit industry, and the many research efforts, the molecular mechanisms involved in pathogenesis are still not fully characterized. In particular, the precise mechanism of recognition/communication between Psa and its host plant has not been yet elucidated. Our findings shows that plant crude extracts or xylem juices of Actinidia deliciosa and A. chinensis were able to increase Psa virulent in comparison with artificial growing media such as Luria Broth or Nutrient agar. The study of gene expression in response to plant-based or artificial growing medium was performed by QPCR and showed a differential expression of many virulence related genes. Also genes related with biofilm formation, motility and inter cell signaling (e.g. quorum sensing in the broad sense) were differencially expressed according to the type of growing media. Interestringly, many of the studied gene expression responded differentially depending both to plant extracts and Psa cell density. The molecular data were corroborated by phenological studies aiming to test the effect of plant based medium on biofilm formation, motility and symptom development in microcuttings of Actinidia spp. The effect of other plant extracts such as tobacco, tomato, tea, hazelnut and A. arguta were also studied to determine whether the activation of genes and phenotypes observed is related to a non specific plant molecules. To determine which plant molecules are specifically recognized by PSA, the putative bacterial receptors have been cloned, expressed heterologously, purified and immobilized in chromatographic columns in order to capture their ligands present in those plant extracts specifically activating Psa genes. The presented study demonstrates the existence of a not yet identified, host-specific group of molecules able to active the pathogenesis machinery of Psa. Moreover these molecules could led to different physiological and molecular behavior depending on Psa population density. Finally, it was also demonstrated that these molecules were differentially present in leaves and xylem sap collected by different Actinidia species.

KNOTTED1-like homeobox (KNOX) genes act in the shoot apical meristem (SAM) to provide an uncommitted population of cells for organogenic programs. In addition to playing a role in SAM function and leaf morphology, there is also evidence of the involvement of KNOX genes in some features of flower development. The expression pattern of HtKNOT1, a class I KNOX gene, in inflorescence meristems, floral meristems and floral organs of two related species, Helianthus tuberosus and H. annuus strengthens this view. HtKNOT1 mRNAs have been detected in the inflorescence and floral meristems as well within lateral organ primordia (i.e. floral bracts, petals, stamens and carpels). In more differentiated flowers, the expression of HtKNOT1 was restricted to developing ovules and pollen. Class I KNOX genes may play a dual role being required to maintain the meristem initials as well as initiating differentiation and/or conferring new cell identity. In the genus Helianthus, some KNOX genes could cooperate at the floral level with additional factors that more specifically control floral organs and pollen development.

Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, was first isolated in 1989. A pandemic outbreak that started in 2008 is seriously threatening kiwifruit production worldwide. Very little is known about the molecular mechanisms involved in this host-pathogen interaction. In this study, an RNAseq approach was applied to identify the virulence genes of Psa involved in pathogenicity. Transcriptome analysis was carried out on Psa grown in LB medium (PsaLB) or in LB medium supplemented with plant extracts of Actinidia deliciosa (PsaAd) or Actinidia chinensis (PsaAc). Differential gene expression analysis under all three tested conditions highlighted widespread transcriptional modulation, with up to 2000 genes listed as significantly differentially expressed genes (DEGs), which represents about half of the total number of Psa genes. Many of the genes found to be upregulated in Psa cells exposed to plant extracts were involved in functions such as motility, chemotaxis, adherence and iron acquisition, which are functions associated with plant colonization. However, under the PsaAd and PsaAc conditions, genes coding for the type-III secretion system and type-III effector proteins, which are known to be essential for virulence of P. syringae, were downregulated. These data suggest that regulation of the expression of type-III secretion system genes was dependent on plant signals distinct from those that control expression of genes involved in motility, and invasion and might require direct interaction with plant cells in intact tissue.

† Background and Aims The clone EMB-2 of the interspecific hybrid Helianthus annuusH. tuberosus provides an interesting system to study molecular and physiological aspects of somatic embryogenesis. Namely, in addition to non-epiphyllous (NEP) leaves that expand normally, EMB-2 produces epiphyllous (EP) leaves bearing embryos on the adaxial surface. This clone was used to investigate if the ectopic expression of H. annuus LEAFY COTYLEDON1-LIKE (Ha-L1L) gene and auxin activity are correlated with the establishment of embryogenic competence. † Methods Ha-L1L expression was evaluated by semi-quantitative RT-PCR and in situ hybridization. The endogenous level and spatial distribution of free indole-3-acetic acid (IAA) were estimated by a capillary gas chromatography -mass spectrometry-selected ion monitoring method and an immuno-cytochemical approach. † Key Results Ectopic expression of Ha-L1L was detected in specific cell domains of the adaxial epidermis of EP leaves prior to the development of ectopic embryos. Ha-L1L was expressed rapidly when NEP leaves were induced to regenerate somatic embryos by in vitro culture. Differences in auxin distribution pattern rather than in absolute level were observed between EP and A-2 leaves. More precisely, a strong IAA immuno-signal was detected in single cells or in small groups of cells along the epidermis of EP leaves and accompanied the early stages of embryo development. Changes in auxin level and distribution were observed in NEP leaves induced to regenerate by in vitro culture. Exogenous auxin treatments lightly influenced Ha-L1L transcript levels in spite of an enhancement of the regeneration frequency. † Conclusions In EP leaves, Ha-L1L activity marks the putative founder cells of ectopic embryos. Although the ectopic expression of Ha-L1L seems to be not directly mediated by auxin levels per se, it was demonstrated that localized Ha-L1L expression and IAA accumulation in leaf epidermis domains represent early events of somatic embryogenesis displayed by the epiphyllous EMB-2 clone.