Aluminum-Induced Gene Expression and Protein Localization of a Cell Wall-Associated Receptor Kinase in Arabidopsis

Abstract

Here, we report the aluminum (Al)-induced organ-specific expression of a WAK1 (cell wall-associated receptor kinase 1) gene and cell type-specific localization of WAK proteins in Arabidopsis. WAK1-specific reverse transcriptase-polymerase chain reaction analysis revealed an Al-induced WAK1 gene expression in roots. Short-and long-term analysis of gene expression in root fractions showed a typical "on" and "off" pattern with a first peak at 3 h of Al exposure followed by a sharp decline at 6 h and a complete disappearance after 9 h of Al exposure, suggesting the WAK1 is a further representative of Al-induced early genes. In shoots, upon root Al exposure, an increased but stable WAK1 expression was observed. Using confocal microscopy, we visualized Al-induced closure of leaf stomata, consistent with previous suggestions that the Al stress primarily experienced in roots associated with the transfer of root-shoot signals. Elevated levels of WAK protein in root cells were observed through western blots after 6 h of Al exposure, indicating a lag time between the Al-induced WAK transcription and translation. WAK proteins are localized abundantly to peripheries of cortex cells within the elongation zone of the root apex. In these root cells, disintegration of cortical microtubules was observed after Al treatment but not after the Al analog lanthanum treatments. Tip-growing control root hairs, stem stomata, and leaf stomatal pores are characterized with high amounts of WAKs, suggesting WAKs are accumulating at plasma membrane domains, which suffer from mechanical stress and lack dense arrays of supporting cortical microtubules. Further, transgenic plants overexpressing WAK1 showed an enhanced Al tolerance in terms of root growth when compared with the wild-type plants, making the WAK1 one of the important candidates for plant defense against Al toxicity.

Duplicate and Conquer: Multiple Homologs ofPHOSPHORUS-STARVATION TOLERANCE1Enhance Phosphorus Acquisition and Sorghum Performance on Low-Phosphorus Soils

“…Indeed, expression of WAK1 in Arabidopsis was found to be induced by aluminum treatment (Sivaguru et al, 2003), and WAKL4 is related to mineral nutrition responses (Hou et al, 2005). Wall-associated kinases are necessary for normal cell enlargement (Cosgrove, 2001;Wagner and Kohorn, 2001), and in barley and rice, WAK genes were found to affect root growth Gupta, 2008, 2011;Kaur et al, 2013).…”

RESISTANCE TO FUSARIUM OXYSPORUM 1, a Dominant Arabidopsis Disease-Resistance Gene, Is Not Race Specific

“…An inducible reduction in WAK protein accumulation has been shown to reduce plant cell expansion and result in stunting of roots and shoots (Lally et al 2001;Wagner and Kohorn 2001). On the other hand, ectopic overexpression of WAK1 has been shown to increase tolerance of roots to toxic aluminum concentrations (Sivaguru et al 2003). Also, root elongation in loss-of-function mutations of either WAKL4 or WAKL14 is reported to be more or less tolerant to certain metal ion stresses ( Jackson et al 2004).…”

RNAi mediated silencing of a wall associated kinase, OsiWAK1 in Oryza sativa results in impaired root development and sterility due to anther indehiscence

“…Arabidopsis demonstrated that they are involved in various functions of plants, including pathogen resistance (He et al 1998), heavy metal tolerance (Sivaguru et al 2003) cell elongation and plant development (Lally et al 2001;Wagner and Kohorn 2001).…”

“…WAKs are encoded by five tightly linked and highly similar genes (WAK1-WAK5) in Arabidopsis thaliana, and are expressed in leaves, meristems and cells undergoing expansion (He et al 1996(He et al , 1999Wagner and Kohorn 2001). WAK gene expression is also induced by pathogens, wounding, Aluminum toxicity and numerous other stresses (He et al 1996;Wagner and Kohorn 2001;Sivaguru et al 2003).…”