Occurrence of plant-specific 4/1 gene in streptophyte algae: brief view on the gene and protein evolution

Previously, the plant-specific 4/1 proteins have been found to be encoded by single-copy genes in most land plants (clade Embryophyta) but not in green algae. We first identified and characterized 4/1 genes in arabidopsis (At-4/1) and tobacco (Nt-4/1). Importantly, the 4/1 proteins in Magnoliophyta species are characterized by a highly conserved C-terminal domain of 30-37 amino acids. In this paper, we report the analysis of 4/1 genes in streptophyte algae - ancestors of lower land plants. AUGUSTUS ab initio gene prediction was used to predict 4/1 protein-coding genes in the chromosomal DNA sequences of several algae from classes Mesostigmatophyceae, Klebsormidiophyceae and Zygnemophyceae. Interestingly, in contrast to an inronless 4/1-like gene previously found in another charophyte alga Chara braunii, these genes contain several introns that is consistent with the 4/1 exon-intron organization of land plants. In general, the chromosomes of the studied charophyte algae were found to encode Magnoliophyta-like 4/1 proteins that share their previously described general gene structure and protein properties. These new data on the 4/1-like genes and proteins in the Streptophyta clade suggest that 4/1 proteins are probably function as accessory factors in stress response, but these polypeptides are not required for the primary metabolic functions of streptophyte cells.