Crosstalk between ABA signaling and GA metabolism for the determination of the dormancy level of developing Sorghum caryopses.

BENECH ARNOLD R.L.

Changsha

Congreso; 11 th Conference of the International Society for Seed Science; 2014

ISSS

Gibberellin levels are highly associated with the pre-harvest sprouting (PHS) response of two grain sorghum lines, IS9530 and RedlandB2 IS9530 line shows high dormancy at maturity and this is in accordance with high SbGA2oxC gene (encoding a putative GA inactivation enzyme) expression during grain incubation. Also, GA34 (catabolite) levels correlated negatively with GA4 accumulation in grains of both lines, further supporting that inactivation is a key process in determining active GA content in the embryo. Promoter sequences of this gene contain several cis-regulatory elements involved in ABA signalling regulation (ABREs). In addition, SbABI5 and SbABI4 gene expression followed a similar temporal accumulation pattern to the gene mentioned above, indicating that a possible interaction between SbGA2oxC gene promoter and ABI5 and ABI4 may occur. Therefore, this possibility was assesseds since it could be an important control point to regulate PHS in sorghum crops. A 1056 bp fragment of SbGA2oxC promoter upstream the initiation codon was cloned and sequenced for both sorghum lines. Sequences differed in three bases at positions -294, -521 and -770, one of which (at -294 position) resulted in the appearance of a new binding site for WRKY transcription factors in IS9530 (some of them reported to be involved in GA signalling response). To study possible interactions between ABI4 and ABI5 protein and SbGA2oxC promoter, recombinant ABI 4 and ABI5 was overexpressed in bacteria and purified. EMSA studies were carried out to test binding to the SbGA2oxC promoter. Both transcription factors were able to bind the promoter, although not simultaneously, suggesting that they might compete for the same cis-acting regulatory sequences. A comparative analysis of the 5`regulatory region of GA2oxs from both monocots and dicots was also carried out; conservation of the ABRC (ABA responsive complex) in closely related GA2oxs from Brachypodium and rice suggest that these species might share the same regulatory mechanism as proposed for grain sorghum.