Identification of GROWTH-REGULATING FACTOR transcription factors in lettuce ( Lactuca sativa ) genome and functional analysis of LsaGRF5 in leaf size regulation

Background GROWTH-REGULATING FACTORs (GRFs), a type of plant-specific transcription factors, play important roles in regulating plant growth and development. Although GRF gene family has been identified in various plant species, a genome-wide analysis of this family in lettuce ( Lactuca sativa L.) has not been reported yet. Results Here we identified 15 GRF genes in lettuce and performed comprehensive analysis of them, including chromosomal locations, gene structures, and conserved motifs. Through phylogenic analysis, we divided LsaGRFs into six groups. Transactivation assays and subcellular localization of LsaGRF5 showed that this protein is likely to act as a transcriptional factor in the cell nucleus. Furthermore, transgenic lettuce lines overexpressing LsaGRF5 exhibited larger leaves, while smaller leaves were observed in LsaMIR396a overexpression lines, in which LsaGRF5 was down-regulated. Conclusions These results in lettuce provide insight into the molecular mechanism of GRF gene family in regulating leaf growth and development and foundational information for genetic improvement of the lettuce variations specialized in leaf character.