Comprehensive review on growth regulating factor (GRF): A transcriptional factor in rice (Oryza sativa)

Rice is the staple food for more than half of the world’s population. Production is a major consideration for a future-demanding, growing population. Plant growth is mediated by several gene expressions. Growth regulating factor (GRF) is a transcription factor (TF) family member, which includes 12 GRF members in rice. Evolutionary analysis of GRF showed that GRF members were found in all land plants, participate in growth, development, metabolism and are involved in defense mechanisms. In rice, 12 members of GRF are expressed in different tissues at different time intervals and regulate leaf size, stem elongation, floral development, grain size improvement and resistance against biotic and abiotic stresses. GRF has two domains, QLQ (glutamine-leucine-glutamine) and WRC (WRKY rich cysteine). GRF TF interacts with a co-activator called GRF-interacting factor (GIF) and GIF harbors an SNF (sucrose nonfermenting 2) domain. This GRF-GIF duo, along with miRNA (micro RNA), regulates downstream target genes.miR396 specifically targets GRFs and functions in the repression of specific GRFs and is upregulated during stress conditions. This complex can be regulated by hormones such as gibberellic acid, brassinosteroid, which have a tremendous effect on the expression of GRF genes under normal and stress conditions. Some of the members are novelly present in some varieties and exhibit their expression, like GS2/GL2 (Grain Size2/ Grain Length2) allele, which regulates grain size. New germplasms harboring GRF function can be created by transgenic approaches, RNAi (RNA interference) methodologies, target mimic approaches and breeding programs. Understanding their structure and function, as well as their regulatory mechanisms across different tissues, can be utilized to target desirable agronomic traits with significant economic value.