MOTIVATION:Full-length transcript reconstruction is very important and quite challenging for the widely used RNA-seq data analysis. Currently available RNA-seq assemblers generally suffered from serious limitations in practical applications, such as low assembly accuracy and incompatibility with latest alignment tools. RESULTS:We introduce iPAC, a new genome-guided assembler for reconstruction of isoforms, which revolutionizes the usage of paired-end and sequencing depth information via phasing and combing paths over a newly designed phasing graph. Tested on both simulated and real datasets, it is to some extent superior to all the salient assemblers of the same kind. Especially, iPAC is significantly powerful in recovery of lowly expressed transcripts while others are not. AVAILABILITY: iPAC is freely available at http://sourceforge.net/projects/transassembly/files. SUPPLEMENTARY INFORMATION:Supplementary data are available at Bioinformatics online.