Validation of reference genes for normalization of qPCR gene expression data from Coffea spp. hypocotyls inoculated with Colletotrichum kahawae.
BACKGROUND
Coffee production in Africa represents a significant share of the total export revenues and influences the lives of millions of people, yet severe socio-economic repercussions are annually felt in result of the overall losses caused by the coffee berry disease (CBD). This quarantine disease is caused by the fungus Colletotrichum kahawae Waller and Bridge, which remains one of the most devastating threats to Coffea arabica production in Africa at high altitude, and its dispersal to Latin America and Asia represents a serious concern. Understanding the molecular genetic basis of coffee resistance to this disease is of high priority to support breeding strategies. Selection and validation of suitable reference genes presenting stable expression in the system studied is the first step to engage studies of gene expression profiling.


RESULTS
In this study, a set of ten genes (S24, 14-3-3, RPL7, GAPDH, UBQ9, VATP16, SAND, UQCC, IDE and β-Tub9) was evaluated to identify reference genes during the first hours of interaction (12, 48 and 72 hpi) between resistant and susceptible coffee genotypes and C. kahawae. Three analyses were done for the selection of these genes considering the entire dataset and the two genotypes (resistant and susceptible), separately. The three statistical methods applied GeNorm, NormFinder, and BestKeeper, allowed identifying IDE as one of the most stable genes for all datasets analysed, and in contrast GADPH and UBQ9 as the least stable ones. In addition, the expression of two defense-related transcripts, encoding for a receptor like kinase and a pathogenesis related protein 10, were used to validate the reference genes selected.


CONCLUSIONS
Taken together, our results provide guidelines for reference gene(s) selection towards a more accurate and widespread use of qPCR to study the interaction between Coffea spp. and C. kahawae.
Plant Systems Biology Lab, Center of Biodiversity, Functional & Integrative Genomics (BioFIG), Science Faculty of Lisbon University, Lisbon 1749-016, Portugal. aafigueiredo@fc.ul.pt.
Andreia
A
Figueiredo
Andreia
A
Loureiro
Dora
D
Batista
Filipa
F
Monteiro
Vítor
V
Várzea
Maria Salomé
MS
Pais
Elijah K
EK
Gichuru
Maria Céu
MC
Silva
D040503:Coffea / Q000235:genetics* / Q000382:microbiology*; D020231:Colletotrichum / Q000502:physiology*; D030541:Databases, Genetic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D018546:Hypocotyl / Q000235:genetics / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction / Q000592:standards*; D012015:Reference Standards; D015203:Reproducibility of Results; D012984:Software
D010940:Plant Proteins