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Expression of the uidA gene controlled by promoters preferentially expressed in the phloem of ‘Carrizo’ citrange transgenic plants Brazil is the world’s largest sweet orange producer, leading also the export of frozen concentrated orange juice. However, the citrus industry is constantly threatened by diseases, particularly those caused by bacteria, such as Huanglongbing (HLB). HLB is considered one of the most harmful citrus diseases, leading the plants to their death. The associated agents of this disease are endogenous bacteria restricted to the phloem of the plants (Candidatus Liberibacter spp.). No resistance has been found in Citrus spp. that could be used in breeding programs. Therefore, biotechnological strategies, such as genetic transformation, could help such programs to introduce genes for disease resistance. It is desirable the use of gene constructs that are preferentially expressed where the bacterium colonizes the plant, i.e., the phloem in plants affected by HLB. This study aimed to evaluate transgenic plants of 'Carrizo' citrange [Poncirus trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] with uidA gene (β-glucuronidase), driven by the promoters of CsPP2.1 (Phloem protein 2) and CsVTE2 (homogentisato fitiltransferase) genes obtained from Citrus sinensis plants. Each promoter specificity was analyzed and gene expression was compared with that induced by the constitutive promoter CaMV35S. Molecular analyses such as Southern blot and qPCR were performed in order to verify the number of transgenic copies in plants and to quantify relative expression of the uidA gene driven by different promoters, respectively. Histological analyses were done in order to identify the exact location of the GUS (uidA) reporter gene expression. Relative expressions of the uidA gene driven by specific promotors were lower than that driven by the CaMV35S constitutive promoter, since the expression was limited to specific tissues. The CsPP2.1 promoter drove the uidA gene expression to the phloem tissue, specifically to the companion cells and sieve elements. On the other hand, CsVTE2 promoter drove the reporter gene expression mainly to the periphery of the cortical parenchyma and to the guard cells, where high number of chloroplasts were present, and also drove the expression to the phloem. Although the CsVTE2 promoter is not phloem-specific, it might be used in gene constructs aiming vascular disease control, since it is involved in physiological processes such as mitigating oxidative stress and photoassimilate phloem loading. The results suggest that CsPP2.1 e CsVTE2 are promising promoters to be used in gene constructs in order to control vascular diseases, such as HLB.

Expressão do gene &lt;i&gt;uid&lt;/i&gt;A sob controle de promotores preferencialmente expressos no floema de plantas transgênicas de citrange \'Carrizo\'