Project description:Citrus and most other fruit crops are commercially propagated via grafting, which ensures trees have consistent fruit traits combined with favorable traits from the rootstock such as soil adaptability, vigor, and resistance to soil pathogens. Breeding new rootstocks requires careful agronomic evaluations, and widespread use of new rootstocks and scions requires graft compatibility with commercially important scions and rootstocks. Graft incompatibility can occur when the scion and rootstock are not able to form a permanent, healthy union. Understanding and preventing graft incompatibility is therefore of paramount importance in the breeding of new fruit cultivars and in the choice of scion and rootstock by growers. The rootstock US-1283 is a citrandarin generated from a cross of ‘Ninkat’ mandarin (Citrus reticulata) and ‘Gotha Road’ #6 trifoliate orange (Poncirus trifoliata). It was released in 2014 after years of field evaluation because of its superior productivity and good fruit quality on ‘Hamlin’ sweet orange (C. sinensis) under Florida’s growing conditions. Subsequently, it was observed that trees of ‘Bearss’ lemon (C. limon) and ‘Valencia’ sweet orange (C. sinensis) grafted onto US-1283 exhibited apparent incompatible and unhealthy growth near the graft union. The incompatibility manifested as stem grooving and necrosis underneath the bark on the rootstock side of the graft. A genetically similar citrandarin rootstock, US-812 (C. reticulata ‘Sunki’ × P. trifoliata ‘Benecke’), is fully graft compatible with the same scions. Transcriptome analysis was performed on the vascular tissues above and below the graft union of compatible US-812 and incompatible US-1283 graft combinations with ‘Bearss’ and ‘Valencia’ to identify expression networks associated with incompatibility and help understand the processes and potential causes of incompatibility in citrus. Transcriptional reprogramming was stronger in the incompatible rootstock than in the grafted scions. Functional analysis of the transcriptional events below the graft unions of US-1283 incompatible combinations revealed differentially expression genes (DEGs) associated with oxidative stress and plant defense, among other pathways, similar to a pathogen-induced immune response localized to the rootstock, although no known pathogens were detected in the assayed plants. These changes were not observed above the graft unions.Differentially expressed genes (DEGs) in US-1283, but not the scions, were associated with oxidative stress and plant defense, among others, similar to a pathogen-induced immune response localized to the rootstock. No pathogen infection was detected. It is hypothesized this response could have been triggered by signaling miscommunications between rootstock and scion either through 1) unknown molecules from the scion that were perceived as danger signals by the rootstock, 2) missing signals from the scion or missing receptors in the rootstock necessary for the formation of a healthy graft union, 3) the overall perception of the scion by the rootstock as non-self, or 4) a combination of the above.

Project description:The deficit of oxygen in plants is a frequent phenomenon in nature. The main causes may be due to flooding or excessive irrigation or to an excess of aerobic microflora in the soil. The Intergovernmental Panel on Climate Change (IPCC) reported that the anthropogenically induced change of world climate increases the frequency of heavy precipitation and tropical cyclone activity. This is likely to engender more frequent flooding events in river flood plains and arable farmland, particularly affecting the world’s poorest farmers. The stress caused by lack of oxygen in plants mainly produces a reduction of the respiration, and then a low energy production and accumulation of toxic compounds of anaerobic metabolism. To alleviate this problem plants have developed morphological and metabolic adaptations, the main of which include the induction of anaerobic and fermentative pathways. In the present study we used a Combimatrix platform, made up of around 8,000 ESTs of roots isolated in citrus and its rootstocks. The chip was hybridized with RNA wild type Carrizo citrange roots and a transgenic line highly expressing a transcription factor involved in the response to the deficiency of oxygen in Oryza sativa. The aim of the work consists in the study of the up and down expressed genes in wild type and transgenic lines subjected and not to anaerobiosis, in order to understand the mechanisms that are activated under anoxia. In general, the hybridization of the chip has led to the activation of 492 genes, of which 28.95% is involved in redox processes, 28.41% in the response to stress, 18.28% in response to chemical stimuli. The up and down-regulation of differentially expressed transcripts in response to oxygen deficiency were confirmed through real-time RT-PCR The results obtained showed the activation of main genes involved in the glycolytic and fermentative pathways, such as pyruvate decarboxylase, alcohol dehydrogenase and sucrose synthase. In transgenic plants of Carrizo the response to oxygen deficit appears to be more pronounced, therefore genes of glycolytic, fermentation and pentose phosphate pathway are activated.

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Citrus sinensis x Citrus trifoliata

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