Characterization of PROFILIN genes from allotetraploid (Gossypium hirsutum) cotton and its diploid progenitors and expression analysis in cotton genotypes differing in fiber characteristics.

The actin-binding protein profilin (PRF) plays an important role in cell growth and expansion by regulating the organization of the actin filaments. Recent studies have reported association between fiber elongation in cultivated cotton (Gossypium hirsutum) and PRF expression. In the present study, we cloned four genomic clones from allotetraploid cotton (G. hirsutum) and its putative diploid progenitors (G. arboreum and G. raimondii) designated GhPRF1_A, GhPRF1_D, GaPRF1, and GrPRF1 encoding cotton PRF and characterized their genomic structure, phylogenetic relationships and promoter structure. Sequence analysis of the coding regions of all clones resulted in a single protein product which revealed more than 80% similarity to most plant PRFs and a typical organization with an actin-binding and a polybasic phospholipid binding motif at the carboxy terminus. DNA blot hybridization suggested that PRF gene is present with more than one copy in the allotetraploid species G. hirsutum. Expression analysis performed in various organs of cultivated cotton revealed that the PRF gene was preferentially expressed in cotton fibers. Very low levels of expression were observed in whole flowers, while PRF transcripts were not detected in other organs examined. Furthermore, higher levels of expression were observed at the early stages of cotton fiber development (at 10 days post anthesis), indicative that this gene may play a major role in the early stages of cotton fiber development. Quantitation of the expression by real-time PCR revealed higher expression levels in a G. hirsutum variety with higher fiber percentage compared to a variety with lower percentage. In addition, higher levels of expression were found in cultivated allotetraploid G. barbadense cotton species with higher fiber length in comparison to cultivated allotetraploid G. hirsutum.