importance of cDNA sequencing of a specific gene in different plants
No, cDNAs are copies of spliced mRNAs, and typically contain a 5'-UTR (untranslated region), an open reading frame, or ORF, and a 3'-UTR.
The cis-regulatory information might be revealed by sequencing the genomic DNA upstream of the gene(s).  That is where one usually finds the promoter (although there are some rare exceptions, particularly for genes transcribed by RNA polymerase III).