Expression of sunflower cytochrome c mRNA is tissue-specific and controlled by nitrate and light

A PCR-based strategy with two degenerate oligonucleotides followed by library screening was used to isolate a 590-bp cDNA clone encoding a full-length apocytochrome c polypeptide from a sunflower (Helianthus annuus L. line HA401B) root library. The sequence of the encoded polypeptide (112 amino acids) differs from the previously reported protein sequence (Ramshaw et al. 1970. Biochem. J. 119: 535-539) at four positions. Southern blot analysis indicates the possible existence of tyro different cytochrome c genes in sunflower. The isolated cDNA clone was used to perform expression studies of cytochrome c mRNA(s) in different sunflower organs and under different conditions. Higher transcript levels were observed in flowers and roots relative to leaves, stems, hypocotyls and cotyledons. Light promoted an increase in the expression of cytochrome c mRNA in 6-day-old seedlings. Nitrate treatment, in tum, reduced expression in roots. It is concluded that the steady-state mRNA levels of cytochrome c encoding transcripts in sunflower are subject to tissue-specific regulation and also respond to environmental factors.