Identification of GROWTH-REGULATING FACTOR Transcription Factor Family Involved in Leaf Growth Regulation in Lettuce (Lactuca sativa L.)

Abstract 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 GRF gene family in lettuce (Lactuca sativa L.) has not been reported yet. Results: Here we identified 15 members of GRF genes in lettuce and performed comprehensive analysis of them, including chromosomal locations, gene structures, and conserved motifs. Through phylogenic analysis between GRF genes in Arabidopsis and rice, we divided LsaGRFs into six groups. Specifically, the N-terminal of LsaGRF5 showed transcriptional activity, LsaGRF5 probably functioned as a transcriptional factor in cell nucleus. Meanwhile, 14 LsaGRF genes were predicted to be the target of Lsa-miR396 except of LsaGRF9 using free energies of duplex structures. LsaGRF5 could be cleaved by Lsa-miR396 at specific binding site between the 9th and 10th nucleotides. Furthermore, overexpression of LsaGRF5 in lettuce 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.