Minimum sample size for correlation of expression

Question

[imaditi1987]

Dear All, I am working to find bidirectional promoters in Brassica rapa genome. To find the correlation of expression values between a pair of genes, I am using a RNA seq data which has 8 samples of different tissues. Although there are some microarray data and RNA seq data available which has more number of samples, but, there the sample is either confined to one physiological state, tissue or stress condition and so I am hesitant to use them. Do you think 8 samples is good enough number for correlation analysis or it does not make sense to use such a small sample size.

Thank you