Identification of Genes Involved in the Responses of Tangor (C. reticulata × C. sinensis) to Drought Stress.

Drought is the major abiotic stress with adverse effects on citrus, decreasing the agronomical yield and influencing the fruit quality. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique was used to investigate the transcriptional profile changes and identify drought-responsive genes in "Amakusa" tangor (C. reticulata × C. sinensis), a hybrid citrus sensitive to water stress. The 255 out of 6,245 transcript-derived fragments (TDFs) displayed altered expression patterns including (A) induction, (B) repression, (C) upregulation, and (D) downregulation. With BLAST search, the gene products of differentially expressed fragments (DEFs) could be classified into several categories: cellular processes, transcription, transport, metabolism, stress/stimuli response, and developmental processes. Downregulated genes were highly represented by photosynthesis and basic metabolism, while upregulated ones were enriched in genes that were involved in transcription regulation, defense, energy, and transport. Present result also revealed some transient and up- and then downregulated genes such as aquaporin protein and photosystem enzyme. Expression patterns of 17 TDFs among 18 homologous to function-known genes were confirmed by qRT-PCR analysis. The present results revealed potential mechanism of drought tolerance in fruit crop and also provided candidate genes for future experiments in citrus.

[Identification of AFLP markers linked to bacterial wilt resistance gene in tomato].

A cross between bacterial wilt resistant tomato variety "T51A"and susceptible variety 'T9230' was made for mapping bacterial wilt resistance gene(s). Through inoculation test of its F1 and F2 progeny, it was proved that the resistance of 'T51A' to bacterial wilt was controlled by one heterozygous gene and cytoplasm. With 64 EcoR I/Muse I primer combinations, AFLP analysis was performed on two parents and their F2 resistant and susceptible bulks. A total of about 4200 distinguishable bands were amplified, of which two were stable. Genetic linkage analysis of the two polymorphic DNA fragments with the resistance gene(s) was tested in the F2 segregating population derived from the cross between 'T51A' and 'T9230'. The DNA fragment AAG/CAT was found closely linked to one of the bacterial wilt resistant genes, with a genetic distance of 6.7 cM, that was tentatively named RRS-342. The cloned fragment AAG/CAT was sequenced and then successfully converted to a SCAR marker, which can be used more conveniently in marker-assisted selection for tomato resistance to bacterial wilt gene.