Nylon Filter Arrays Reveal Differential Gene Expression in Proteoid Roots of White Lupin in Response to Phosphorus Deficiency

Abstract

White lupin (Lupinus albus) adapts to phosphorus deficiency (ϪP) by the development of short, densely clustered lateral roots called proteoid (or cluster) roots. In an effort to better understand the molecular events mediating these adaptive responses, we have isolated and sequenced 2,102 expressed sequence tags (ESTs) from cDNA libraries prepared with RNA isolated at different stages of proteoid root development. Determination of overlapping regions revealed 322 contigs (redundant copy transcripts) and 1,126 singletons (single-copy transcripts) that compile to a total of 1,448 unique genes (unigenes). Nylon filter arrays with these 2,102 ESTs from proteoid roots were performed to evaluate global aspects of gene expression in response to ϪP stress. ESTs differentially expressed in P-deficient proteoid roots compared with ϩP and ϪP normal roots include genes involved in carbon metabolism, secondary metabolism, P scavenging and remobilization, plant hormone metabolism, and signal transduction.Phosphorus (P) is an essential macronutrient for plant growth and development that plays key roles in many processes, including energy metabolism and synthesis of nucleic acids and membranes (Raghothama, 1999). It is second only to nitrogen as the most limiting nutrient for plant growth (Bieleski, 1973; Raghothama, 1999;. In many soils, low availability of P is a limiting factor in crop production . Due to the low availability of soluble P in many ecosystems, plants have developed adaptive mechanisms that aid in the acquisition of P from soil. Strategies that lead to better uptake or acquisition include expanded root surface area through increased root growth and root hair development (Lynch and Brown, 1998;Gilroy and Jones, 2000; Williamson et al., 2001), organic acid synthesis and exudation (Dinkelaker et al., 1989;Johnson et al., 1996a;Jones, 1998; Aono et al., 2001;Massonneau et al., 2001; Sas et al., 2001), exudation of acid phosphatases (Duff et al., 1991; del Pozo et al., 1999;Gilbert et al., 1999;Miller et al., 2001), enhanced expression of phosphate transporters (Leggewie et al., 1997;Liu et al., 1998aLiu et al., , 1998b Chiou et al., 2001;Liu et al., 2001), and mycorrhizal associations (Marschner and Dell, 1994; Smith et al., 1994). Strategies aimed at conserving P involve internal remobilization of P and use of alternative metabolic pathways (Theodorou et al., 1992; Theodorou and Plaxton, 1993;Plaxton and Carswell, 1999).White lupin (Lupinus albus), a species known for its extreme tolerance for low P availability, has proven an illuminating model system for understanding plant adaptations to low P, despite its lack of mycorrhizal symbiosis. Instead, its adaptation to P deficiency (ϪP) is a highly coordinated modification of root development and biochemistry resulting in proteoid (or cluster) roots-short, densely clustered tertiary roots-that resemble bottlebrushes (Gardner et al., 1982(Gardner et al., , 1983Dinkelaker et al., 1995;Johnson et al., 1996b;Neumann et al., 1999;Massonneau et al., 2001). Unlike typical...

A genome-wide transcriptional analysis using Arabidopsis thaliana Affymetrix gene chips determined plant responses to phosphate deprivation

“…2). These results are in agreement with results from the smaller microarrays with Arabidopsis, rice, and white lupin showing similar patterns of gene expression (7)(8)(9)(10). The differential expression of Pi-responsive genes is considered an adaptive response by plants to Pi deficiency, which facilitate acquisition of sparingly available Pi and concurrent attenuation of some of the energy-requiring metabolic pathways (21).…”

“…This technical limitation has now been circumvented by recently developed microarray technology, which has been used successfully to study the effects of different abiotic stresses to large number of plant genes in parallel (6). To date, relatively small microarrays containing probes for less than one-third of all genes have been used in Arabidopsis, rice, and white lupin to monitor molecular responses to Pi deprivation (7)(8)(9)(10). In Arabidopsis, the expression of Ϸ29% of 6,172 genes examined changed in response to Pi starvation for up to 3 days (10).…”

Update on White Lupin Cluster Root Acclimation to Phosphorus Deficiency Update on Lupin Cluster Roots

“…Moreover, white lupin roots impaired for endogenous auxin transport by being grown in the presence of the auxin transport inhibitor N-1-naphthylphthalamic acid failed to form induced cluster roots under P deficiency (Gilbert et al, 2000). Many genes involved in auxin synthesis and signaling are abundantly expressed in developing cluster roots of white lupin (Uhde-Stone et al, 2003b;Vance et al, 2003;Yamagishi et al, 2011). These data clearly show that a significant component of P-induced cluster root formation is due to auxin synthesis and transport.…”

“…They postulated that auxin stimulates the emergence of cluster rootlets in P-deficient plants, which results in increased production of cytokinin due to the numerous emerged root tips. In mature segments of P-induced cluster roots, we have found ESTs that annotate to cytokinin oxidase (CKX; Uhde-Stone et al, 2003b), suggesting that cytokinins are involved in cluster root development and maturation. We have recently transformed white lupin roots with a white lupin CKX:GUS reporter and a Medicago cytokinin receptor (CRE):GUS reporter.…”

Physiological and Biochemical Mechanisms of Plant Adaptation to Low-Fertility Acid Soils of the Tropics: The Case of Brachiariagrasses

“…Recent advances in post-genomic studies have indicated that transcriptomic analysis is a useful tool for understanding gene expression networks. Some transcriptomic studies of www.intechopen.com low-P adaptation strategies have also been carried out using cDNA arrays (Hammond et al, 2003;Misson et al, 2005;Ramaekers et al, 2010;Uhde-Stone et al, 2003;Wang et al, 2002;Wasaki et al, 2003bWasaki et al, , 2006Wu et al, 2003). Although some aspects of plant strategies for coping with P-deficient conditions are understood, the majority are not; a broad view of gene expression is necessary to fully elucidate all of the mechanisms involved (Ramaekers et al, 2010).…”