GRAS and DELLA protein
Authors: Sukumar Taria1 and Gopa Mishra2
1 Scientist, Plant Science, Krishi Vigyan Kendra, OUAT BBSR
2 Ph D scolar, Department of fruit science, OUAT BBSR

GRAS proteins are an important family of plant-specific proteins derived its name after the first three members: GIBBERELLICACID INSENSITIVE (GAI), REPRESSOR of GAI (RGA) and SCARECROW (SCR). There are at least 33 and 60 GRAS genes has been identified in rice and Arabidopsis respectedly.

GRAS proteins are typically 400-700 amino acids in length and consist of several distinct motifs in their carboxyl (C-) termini, found in the following order: leucine heptad repeat I (LHR I), VHIID, leucine heptad repeat II (LHR II), PFYRE and the SAW motif. The GRAS protein family can be divided into eight subfamilies that have been named either after their members or after a common motif: DELLA, HAM, LISCL, PAT1, LS, SCR, SHR and SCL3 subfamilies. DELLA represent the aspartic acid(D), glutamic acid(E), leucine( L),leucine(L) and alanine(A),HAM ( Hairy meristem),LISCL(Lilium longiforum SCR-like),PAT1( Phytochrome A signal transduction),SHR( short root),SCR( scare crow).

Most GRAS family members possess a variable N-terminal domain (N-domain) and a widely and highly conserved C terminal domain (GRAS domain).

DELLAs: Role In Giberellin And Light Signalling

DELLA protein the negative regulator of gibberelin signallling..The plant hormone GA is perceived by the nuclear receptor GA-INSENSITIVE DWARF1 (GID1) and GA-binding facilitates the formation of a ternary complex of GA, GID1 and the N-terminal domain of DELLA proteins. This interaction induces a conformational change leading to the recruitment of DELLAs by the F-box proteins SLEEPY1 (SLY1) and GA-INSENSITIVE DWARF2 (GID2) to an E3 ubiquitin ligase complex. The E3 ubiquitin ligase SKP1-Cullin-F-box (SCFSLY1/GID1).

The E3 ubiquitin ligase SKP1-Cullin-F-box (SCFSLY1/GID1) complex polyubiquitinates DELLA proteins and results in their degradation by the 26S proteasome. The digradation of DELLA proteins stimulates GA responsive processes such as seed germination.

In addition to that DELLA protein is involved in interaction with phytochrome interacting factor(PIFs). In the absence of GA DELLA proteins interact strongly with the light-responsive transcription factors PIF3 and PIF4 and prevent them from binding to their target promoters by sequestering these factors into an inactive complex. GA-induced degradation of DELLAs releases PIF3 and PIF4 allowing them to regulate gene expression and promoting growth.

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GRAS and DELLA Protein