Structure, organization and evolution of ADP-ribosylation factors in rice and foxtail millet, and their expression in rice

ADP-ribosylation factors (ARFs) have been reported to function in diverse physiological and molecular activities. Recent evidences also demonstrate the involvement of ARFs in conferring tolerance to biotic and abiotic stresses in plant species. In the present study, 23 and 25 ARF proteins were identified in C3 model- rice and C4 model- foxtail millet, respectively. These proteins are classified into four classes (I-IV) based on phylogenetic analysis, with ARFs in classes I-III and ARF-like proteins (ARLs) in class IV. Sequence alignment and domain analysis revealed the presence of conserved and additional motifs, which may contribute to neo- and sub-functionalization of these proteins. Promoter analysis showed the presence of several cis-regulatory elements related to stress and hormone response, indicating their role in stress regulatory network. Expression analysis of rice ARFs and ARLs in different tissues, stresses and abscisic acid treatment highlighted temporal and spatial diversification of gene expression. Five rice cultivars screened for allelic variations in OsARF genes showed the presence of allelic polymorphisms in few gene loci. Altogether, the study provides insights on characteristics of ARF/ARL genes in rice and foxtail millet, which could be deployed for further functional analysis to extrapolate their precise roles in abiotic stress responses.