The Trinity documentation says:
If you have strand-specific data, specify the library type. There are four library types:
- Paired reads:
- RF: first read (/1) of fragment pair is sequenced as anti-sense (reverse(R)), and second read (/2) is in the sense strand (forward(F)); typical of the dUTP/UDG sequencing method.
- FR: first read (/1) of fragment pair is sequenced as sense (forward), and second read (/2) is in the antisense strand (reverse)
- Unpaired (single) reads:
- F: the single read is in the sense (forward) orientation
- R: the single read is in the antisense (reverse) orientation
The TopHat manual says:
Library Type Examples Description
fr-unstranded Standard Illumina Reads from the left-most end of the fragment (in transcript coordinates) map to the transcript strand, and the right-most end maps to the opposite strand.
fr-firststrand dUTP, NSR, NNSR Same as above except we enforce the rule that the right-most end of the fragment (in transcript coordinates) is the first sequenced (or only sequenced for single-end reads). Equivalently, it is assumed that only the strand generated during first strand synthesis is sequenced.
fr-secondstrand Ligation, Standard SOLiD Same as above except we enforce the rule that the left-most end of the fragment (in transcript coordinates) is the first sequenced (or only sequenced for single-end reads). Equivalently, it is assumed that only the strand generated during second strand synthesis is sequenced.
To complete that, in Trinity fr-firststrand
corresponds to RF
and fr-secondstrand
corresponds to FR
.
You can have a look here: http://rnaseq.uoregon.edu. They well explain the difference between first-strand and second-strand synthesis.
You can also have look to this publication: Sequencing technologies - the next generation. Nature reviews. Genetics. 2010. doi:10.1038/nrg2626
Briefly, if you know the technology used for the sequencing you should be able to guess.
Was this paired end?