Expression of Seed Dormancy in Grain Sorghum Lines with Contrasting Pre-Harvest Sprouting Behavior Involves Differential Regulation of Gibberellin Metabolism Genes

MA. VERÓNICA RODRÍGUEZ; GUILLERMINA M. MENDIONDO; RENATA CANTORO; GABRIELA A. AUGE; VIRGINIA LUNA; OSCAR MASCIARELLI; ROBERTO L. BENECH-ARNOLD

PLANT AND CELL PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: OXFORD; Año: 2011 vol. 53 p. 64 - 80

0032-0781

Grain sorghum (Sorghum bicolor (L) moench) exhibits intra-specific variability for the rate of dormancy release and pre-harvest sprouting behavior. Two inbred lines with contrasting sprouting response were compared: IS9530 (resistant) and RedlandB2 (susceptible). Precocious dormancy release in RedlandB2 is related to an early loss of embryo sensitivity to abscisic acid and higher levels of gibberellins in imbibed grains as compared to IS9530. With the aim to identify potential regulatory sites for GA metabolism involved in the expression of dormancy in immature grains of both lines, we carried out time course analysis of transcript levels of putative GA metabolism genes and hormone content (GA1, 4, 8, 34). Lower embryonic GA4 level in dormant IS9530 was related to a sharp and  transient induction of two  SbGA2-oxidase  (inactivation) genes. In contrast, these genes were not induced in less dormant RedlandB2, while expression of two GA20-oxidase (synthesis) genes increased together with active GA4 levels before radicle protrusion. Embryonic levels  of GA4 and its catabolite GA34 correlated negatively. Thus, in addition to the process of GA synthesis, inactivation is also important in regulating GA4 levels in immature grains. A negative regulation by GAs was observed for SbGA20ox2, SbGA2ox1 and 3 and also for SbGID1 encoding a GA receptor. We propose that the coordinated regulation at the transcriptional level of several GA metabolism genes identified in this work affects the balance between GA synthesis and inactivation processes, controlling active GA4 levels during the expression of dormancy in maturing sorghum grains.