Abstract
The study of tolerance mechanisms for drought stress in soybean is fundamental to the understanding and development of tolerant varieties. Using in silico analysis, four marker genes involved in the classical ABA-dependent and ABA-independent pathways of drought response were identified in the Glycine max genome in the present work. The expression profiles of the marker genes ERD1-like, GmaxRD20A-like, GmaxRD22-like and GmaxRD29B-like were investigated by qPCR in root samples of drought sensitive and tolerant soybean cultivars (BR 16 and Embrapa 48, respectively), submitted to water deficit conditions in hydroponic and pot-based systems. Among the four putative soybean homologs to Arabidopsis genes investigated herein, only GmaxRD29B-like was not regulated by water deficit stress. Distinct expression profiles and different induction levels were observed among the genes, as well as between the two drought-inducing systems. Our results showed contrasting gene expression responses for the GmaxRD20A-like and GmaxRD22-like genes. GmaxRD20A-like was highly induced by continuous drought acclimating conditions, whereas GmaxRD22-like responses decreased after abrupt water deprivation. GmaxERD1-like showed a different expression profile for the cultivars in each system. Conversely, GmaxRD20A-like and GmaxRD22-like genes exhibited similar expression levels in tolerant plants in both systems.
Highlights
For soybean (Glycine max [L.] Merrill), one of the most important agricultural commodities in the world (Clemente and Cahoon, 2009), drought is considered as one of the main causes of yield loss in different countries (Bray et al, 2000) In Brazil, the lack of rainfall in 2009 caused a drop of 4.2% in soybean crop production (Brazilian Institute of Geography and Statistics – IBGE, 2010)
In order to identify and characterize Drought Marker Gene (DMG) homologs for ERD1, RD20A, RD22 and RD29B in soybean we initially used an in silico approach, followed by quantitative polymerase chain reaction (qPCR) validation
The digital expression analyses confirmed previous results showing that RD20A, RD22 and RD29B are induced by drought stress and abscisic acid (ABA), whereas ERD1 is induced predominantly by drought stress (Figure S2)
Summary
The losses in soybean yield in the North and West of the state of Paraná (Brazil) related to drought were 80% in 2008-2009, as compared to the average productivity of the region. It has been demonstrated that plants can naturally develop drought tolerance mechanisms, allowing them to prevent or minimize the damaging effects of water deprivation. These response mechanisms involve molecular, cellular and physiological changes, triggered by a molecular signaling cascade (Bray, 1993; Seki et al, 2003; Yamaguchi-Shinozaki and Shinozaki, 2006; Manavalan et al., Neves-Borges et al.2009). This complex network of responses to drought stress may involve the abscisic acid (ABA) phytohormone, which orchestrates the production and accumulation of important molecules that trigger and amplify a signaling cascade (Mahajan and Tuteja, 2005; Adie et al, 2007; Urano et al, 2009)
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