Plant & Animal Genomes XV Conference

January 13-17, 2007
Town & Country Convention Center
San Diego, CA

Transcriptome Comparisons Of Natural And Induced Citrus Mutants By cDNA Microarrays Facilitate The Identification Of Key Genes Involved In Fruit Growth And Development

Enriqueta Alos¹ , Javier Agusti¹ , Javier Brumos¹ , Esther Carrera¹ , Manuel Cercos¹ , Jose M Colmenero-Flores¹ , Ana Consesa¹ , Victoria Ibañez¹ , Domingo J Iglesias¹ , Ignacio Lliso¹ , Antonio Lopez-Usach¹ , Maria I Minguez-Mosquera² , Miguel A Naranjo¹ , Gabino Rios¹ , Maria Roca² , Maria J Rodrigo³ , Jocelyn Rose⁴ , Omar Ruiz¹ , Guillermo Soler¹ , Francisco Tadeo¹ , Javier Terol¹ , Lorenzo Zacarias³ , Manuel Talon¹

¹  Centro de Genómica, Instituto Valenciano de Investigaciones Agrarias (IVIA), Moncada-46113, Valencia, Spain.

²  Chemistry and Biochemistry Pigments Group, Food Biotechnology Department, Instituto de la Grasa, Consejo Superior de Investigaciones Científicas (CSIC), Sevilla 1012, Spain

³  Insituto de Agroquímica de Alimentos (IATA), Burjassot-46110, Valencia, Spain

⁴  Department of Plant Biology, Cornell University, Ithaca, NY 147853, USA

The transcriptome of selected citrus genotypes is being investigated to identify gene functions that in citrus are hardly accessible through genetic approaches. In addition to natural selections, three collections of induced mutated lines (EMS, gamma rays and fast neutrons) composed of about 15000 putative mutants were generated. Gene expression profiles and parallel metabolite analyses are highlighting key genes involved in physiological processes of high agronomical relevance, such as:
Ripening. A MADS and a MYB TF were differently expressed in a mutant showing an overall delay in the ripening gene expression program.
Colour change. The stay green (sgr) mutation that blocks chlorophyll degradation without affecting chlorophyllase activity produced brown dark fruits and strongly down-regulated SGR and HSP transcripts.
Acidity. During pulp ripening the genomic analyses revealed the prevalence of the GABA shunt, a novel and efficient mechanism for citric acid catabolism and reduction of cytoplasmatic acidity. Mutants with low acids also induced gene expression of enzymes involved in tocopherol synthesis.
Volatiles. A gene coding for a terpene synthase was highly repressed in fruits of a mutant with reduced emission of aromatic compounds, mainly the sesquiterpenes linalool and caryophyllene.
Salinity. In addition to genes involved in defence and carbohydrate homeostasis, specific anion and cation channels and active transporters were implicated in chloride-accumulating mutants and /or under salt stress conditions.