Mapping and validation of Xanthomonas citri subsp citri genes regulated by putative plant-inducible promoter box (PIP-box).

Citrus canker, caused by the Gram-negative bacterium Xanthomonas citri subsp citri (Xac), is a major disease affecting citriculture worldwide, because of the susceptibility of the host and the lack of efficient control methods. Previous studies have reported that some genes of phytopathogenic bacteria possess a consensus nucleotide sequence (TTCGC...N15...TTCGC) designated the "plant-inducible-promoter box" (PIP box) located in the promoter region, which is responsible for activating the expression of pathogenicity and virulence factors when the pathogen is in contact with the host plant. In this study, we mapped and investigated the expression of 104 Xac genes associated with the PIP box sequences using a macroarray analysis. Xac gene expression was observed during in vitro (Xac grown for 12 or 20 h in XAM1 induction medium) or in vivo (bacteria grown in orange leaves for 3 to 5 days) infection conditions. Xac grown in non-induction NB liquid medium was used as the control. cDNA was isolated from bacteria grown under the different conditions and hybridized to the macroarray, and 32 genes differentially expressed during the infection period (in vitro or in vivo induction) were identified. The macroarray results were validated for some of the genes through semi-quantitative RT-PCR, and the functionality of the PIP box-containing promoter was demonstrated by activating b-glucuronidase reporter gene activity by the PIP box-containing promoter region during Xac-citrus host interaction.

Differential gene expression in drought-tolerant sugarcane roots.

Drought is one of the most frequent abiotic stresses limiting the productivity and geographical distribution of sugarcane culture. The use of drought-tolerant genotypes is one approach for overcoming the effects of water stress. We conducted a comparative study to identify gene expression profiles under water stress in tolerant sugarcane roots. Two different cultivars, 1 drought tolerant (RB867515) and 1 drought susceptible (SP86-155), were evaluated at 4 sampling time points (1, 3, 5, and 10 days) using the cDNA-amplified fragment length polymorphism technique. A total of 173 fragments were found to be differentially expressed in response to water stress in the tolerant cultivar. Seventy of these were cloned, sequenced, and categorized. Similarity analysis using BLAST revealed that 64% of the fragments differentially expressed code proteins classified as no hits (23%), hypothetical (21%), or involved in stress response (20%), with others were involved in communication pathways and signal transduction, bioenergetics, secondary metabolism, and growth and development. Four genes were analyzed and validated using real-time quantitative polymerase chain reaction to determine their expression and showed consistency with the cDNA-amplified fragment length polymorphism analyses. Our results contribute insight into the molecular responses to water stress in sugarcane and possibility to the development of cultivars with improved tolerance to drought.