Physiological Evidence of Rht1 and Rht2 Genes Expression in few Indian Wheat Cultivars and studying their behaviour in response to exogenous GA3 application

Sood Swati[1], Singh Rupinderpal[2], Chatli S Anshu[3], Mehta Sonam[4] , Kaur Amandeep[5]
Page No. 13-18

The most common dwarfing genes in wheat (Triticum aestivum), Rht-B1b and Rht-D1b, classified
as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA,
have been verified as encoding negative regulators of gibberellin signalling. The introduction of the
reduced height Rht-B1b and Rht-D1b semidwarfing genes led to impressive increases in wheat
(Triticum aestivum) yields during the Green Revolution. The reduction in stem elongation in
varieties containing these alleles is caused by a limited response to the phytohormone gibberellin
(GA), resulting in improved resistance to stem lodging and yield benefits through an increase in
grain number. The phytohormone gibberellin (GA) regulates many plant growth and developmental
processes. Rht-B1 and Rht-D1 encode DELLA proteins, which act to repress GA-responsive
growth, and their mutant alleles Rht-B1b and Rht-D1b are thought to confer dwarfism by producing
more active forms of these growth repressors. The Gibberellin insensitivity of Rht-B1b and Rht-D1b
was confirmed by studying the response of Rht-B1b and Rht-D1b to exogenous GA3 treatment, on
coleoptile length using few Indian wheat cultivars. The application of exogenous GA3 had no
significant effect on coleoptile length of genotypes expressing Rht-B1b and Rht-D1b genes whereas
the coleoptile length of genotypes lacking these genes increased significantly upon exogenous GA3
treatment. It indicates that these newly characterized mutations in Rht-B1 and Rht-D1 confer “GAinsensitive”
dwarfism by producing DELLA proteins that do not bind the GA receptor GA
INSENSITIVE DWARF1, potentially compromising their targeted degradation.
Keywords : wheat (Triticum aestivum), dwarfing genes, gibberellins, lodging, DELLA proteins,
coleoptile length