Expression patterns of cotton chloroplast genes during development: implications for development of plastid transformation vectors

Although most plastid transformation studies have focused on chloroplast expression, plastid transformation can also be used to express genes in plastids of a wide variety of plant tissues by using appropriate plastid promoters. Based on the sequence of the Gossypium hirsutum chloroplast genome, we developed primers and amplified segments of 20 different plastid genes. The PCR products were labeled and used in filter dot blot hybridization studies to characterize their expression levels and patterns in total RNA isolated from light- and dark-grown cotton tissues at different developmental stages. A subset of 6 genes among these was further characterized by real time PCR. Highest expression levels were observed for rrn16 and psbA. Four genes were expressed in all samples at relatively constant levels: accD, atpA, matK and rrn16. Expression in root tissue was generally low. The results of our study can be used to predict which operons and promoters are most likely to be preferentially expressed in the plastids of tissues of interest at levels that would result in the desired phenotype, facilitating the development of plastid transformation vectors.