A Genome-Wide Analysis and Molecular Characterization of SPL Transcription Factors in Alfalfa

The plant-specific transcription factors Squamosa Promoter Binding Protein-Like (SPL) are involved in a range of vital biological and regulatory processes, such as vegetative growth, flowering and stress response. While the SPL gene family has been well studied in some plants, a systematic study has not yet been reported in alfalfa (Medicago sativa). In the present study, a total of 28 novel SPL members, including six alfalfa-specific ones, were identified using in silico C-based analysis of the recently released genome sequence, and named based on their closest orthologs in Medicago truncatula. The SPL-specific SBP domain was detected in all members, and 16 of the 28 members showed miR156 recognition target sequences. Maximum-Likelihood phylogenetic analyses showed the presence of five subclades and three outgroup members. The sequences within groups showed motif conservation, which may imply the presence of redundant functionality between certain SPL members. However, the members overall had divergent motifs indicating diverse functional roles of SPLs in alfalfa. A large number of redundant and/or highly similar sequences observed during synteny analyses revealed extensive gene duplication within the alfalfa genome. This might imply that MsSPL gene expansion stemmed from segmental duplication processes. The present study provides a comprehensive foundation for elucidating the biological functions of these transcription factors and thereby provides new tools for biotechnological improvement of important alfalfa attributes.