Abstract
Proteins containing the SPX domain are believed to play vital roles in the phosphorus (P) signalling network in plants. However, the functions of SPX proteins in legumes remain largely unknown. In this study, three SPX members, PvSPX1-PvSPX3 were cloned from common bean (Phaseolus vulgaris L.). It was found that the transcripts of all three PvSPX members were significantly enhanced in both bean leaves and roots by phosphate (Pi) starvation. Among them, the expression of nuclear localized PvSPX1 showed more sensitive and rapid responses to Pi starvation. Consistently, only overexpression of PvSPX1 resulted in increased root P concentration and modified morphology of transgenic bean hairy roots, such as inhibited root growth and an enlarged root hair zone. It was further demonstrated that PvSPX1 transcripts were up-regulated by overexpressing PvPHR1, and overexpressing PvSPX1 led to increased transcripts of 10 Pi starvation-responsive genes in transgenic bean hairy roots. Taken together, it is suggested that PvSPX1 is a positive regulator in the P signalling network of common bean, and is downstream of PvPHR1.
Highlights
Phosphorus (P) is an essential element for plant growth, and is fixed by soil particles due to its chemical properties
Seeds of common bean genotype G19833 were surface sterilized for 1 min using 10% (v/v) H2O2 and germinated in the dark on germination paper moistened with 1/4 strength modified nutrient solution as described previously (Yan et al, 2001)
After 8 d of Pi starvation, the total P contents of bean shoots and roots were reduced by 32% and 30%, respectively, as compared with high P conditions (Supplementary Table S2)
Summary
Phosphorus (P) is an essential element for plant growth, and is fixed by soil particles due to its chemical properties. Low P availability adversely affects crop growth and production, especially on acid soils (Raghothama, 1999; Vance et al, 2003). To cope with low P stress, plants have developed a wide range of adaptive strategies, such as changes in root architecture and morphology (Liao et al, 2004; Zhou et al, 2008; Péret et al, 2011; Tian et al, 2012), increased exudation of protons and organic acids (Fox and Comerford, 1990; Ström et al, 2005; Taghipour and Jalali, 2012), and enhanced secreted or root-associated acid phosphatase activities These adaptive strategies are tightly mediated by the P signalling network, which is composed of a wide array of regulators (Raghothama, 1999; Vance et al, 2003; Chiou and Lin, 2011)
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