Abstract:
Drought and salt are the two primary abiotic stresses that have a severe negative impact
on rice productivity in Sri Lanka as well as around the world. Rice plants survive the
stress by responding at the molecular, cellular, and organismal levels. Transcription
factors play a critical role in inducing expression of abiotic stress responsive genes, which
leads towards development of higher tolerance to drought, high salinity stress in plants.
In this study, the OsDREB2A gene which is a rice homolog of DREB2A was isolated
from indica rice variety pokkali and HVA1 like promoter was isolated from INGER 46.
By following a transgenic approach, transcription factor OsDREB2A under the
regulation of abiotic stress inducible HVA1 like promoter was introduced to local rice
variety Bg94-l.The highly efficient method reported in this study for Agrobacteriummediated
transformation and development of transgenic rice for Bg94-1 was achieved by
optimizing embryogenic calli induction, Agrobacterium-mediated transformation of
callus cells and ensuing selection and regeneration of intact individual rice plants
containing HVAl-GUS-nos, CaMV35S-GUS-nos, HVAl-OsDREB2A-nos and
CaMV35S-OsDREB2A-nos transgene constructs.
The GUS histochemical analysis and real time Qt-PCR analysis in HVAl-GUS-nos &
CaMV35S-GUS-nos transgenic rice plants subjected to drought and salinity stress
demonstrated the sensitivity of the HVA1 like promoter towards abiotic stresses and
established its role in regulation of gene expression in rice under drought and salinity
stresses. The OsDREB2A transcript levels analyzed by real time Qt-PCR in HVA1-
OsDREB2A-nos rice plants showed an increase in transcript levels as early as 30mins
after rice plants were subjected to drought and salinity stress. However the gradual
increase of the OsDREB2A transcript levels observed in these plants up to 2 hours of
stress demonstrated a decrease after 4 hours. OsDREB2A expression was found to be
markedly induced by drought and salinity treatment.
Induced over-expression of OsDREB2A driven by the HVA1 like promoter in transgenic
rice plants under the drought and salinity stresses was observed showing significant
phenotypic effects such as enhanced root growth, increased dry mass and root mass which
may bring about abiotic stress tolerance in rice.
