Genome-Wide Analysis of the Growth-Regulating Factor Family in Medicago truncatula

Growth-regulating factor (GRF) exerts important functions related to plant development and stress response. However, in Medicago truncatula, the GRF family has not been comprehensively analyzed at the genome level. This study identified eight MtGRF genes (containing both QLQ and WRC domains) in the M. truncatula genome, and no duplicate events occurred between these genes. Gene expression analysis showed that MtGRFs exhibited the highest expression in shoot apical meristems (SAM) followed by seeds, flowers, roots, etc. MtGRF2-6 and MtGRF8 were induced by GA, IAA, and ABA, and MtGRF2 and MtGRF5 also responded to MeJA. Additionally, eight, five, and seven MtGRF genes were differentially expressed under drought, salt, and cold stress, respectively. Five MtGRF genes (MtGRF1, 2, 6, 7, and 8) responded to all three types of stresses, especially MtGRF8, the expression of which was inhibited under drought, salt, and cold stress. These results indicated that MtGRF8 may be a negative regulator of the stress response. Degradome analysis showed that all eight MtGRFs were the target genes of Mt-miR396, and MtGRF4 may be jointly regulated by Mt-miR396 and other microRNAs. These results will contribute to the understanding of the GRF family in M. truncatula.