Mutation in a homolog of yeast Vps53p accounts for the heat and osmotic hypersensitive phenotypes in Arabidopsis hit1-1 mutant

Abstract

Previously, the growth of Arabidopsis hit1-1 (heat-intolerant) mutant was found to be inhibited by both heat and water stress (Wu et al. in J Plant Physiol 157:543-547, 2000). In order to determine the genetic mutation underlying the hit1-1 phenotype, map-based cloning of HIT1 gene was conducted. Transformation of the hit1-1 mutant with a HIT1 cDNA clone reverts the mutant to the heat tolerance phenotype, confirming the identity of HIT1. Sequence analysis revealed the HIT1 gene encodes a protein of 829 amino acid residues and is homologous to yeast (Saccharomyces cerevisiae) Vps53p protein. The yeast Vps53p protein has been shown to be a tethering factor that associates with Vps52p and Vps54p in a complex formation involved in the retrograde trafficking of vesicles to the late Golgi. An Arabidopsis homolog of yeast Vps52p has previously been identified and mutation of either the homolog or HIT1 by T-DNA insertion resulted in a male-specific transmission defect. The growth of yeast vps53Delta null mutant also shows reduced thermotolerance, and expression of HIT1 in this mutant can partially complement the defect, supporting the possibility of a conserved biological function for Vps53p and HIT1. Collectively, the hit1-1 is the first mutant in higher plant linking a homolog of the vesicle tethering factor to both heat and osmotic stress tolerance.

Arabidopsis UNHINGED encodes a VPS51 homolog and reveals a role for the GARP complex in leaf shape and vein patterning

“…The GARP complex is evolutionarily conserved and present in all eukaryotes (Koumandou et al, 2007). Phenotypes resulting from mutation to three subunits (VPS52, VPS53 and VPS54) of the GARP complex in Arabidopsis (Guermonprez et al, 2008;Lee et al, 2006;Lobstein et al, 2004;Wang et al, 2011) suggest that, as in metazoans, the GARP complex has an important developmental role in plants.…”

Tethering Factors Required for Cytokinesis in Arabidopsis

“…In addition, the Exocyst has recently been shown to be required in the stigma for the acceptance of compatible pollen in both Brassica and Arabidopsis (Samuel et al, 2009). Some Arabidopsis GARP mutants have also been implicated in pollen tip growth (Lobstein et al, 2004;Guermonprez et al, 2008) as well as in resistance to heat and osmotic stress (Lee et al, 2006). The TRAPPI and -II complexes, however, have not been studied in plants to date.…”

The Arabidopsishit1-1mutant has a plasma membrane profile distinct from that of wild-type plants at optimal growing temperature

“…4 Map-based cloning led to the identification of HIT1 as a homolog of yeast Vps53p, 5 which is a subunit of the Golgi-associated retrograde protein (GARP) tethering complex that is involved in vesicle trafficking from the endosome to the trans-Golgi network (TGN). 6 Taking advantage of the available hit mutants, Wang et al investigated the causality between HIT1 and plasma membrane thermostability, 7,8 and demonstrated that, while the anti-oxidative capability of hit1-1 plants was equal to that of wild-type plants, significantly more electrolyte leakage from hit1-1 leaves was detected after long term heat exposure (37°C for 24 h).…”

“…How vesicle trafficking machinery participates in this global reorganization of membrane lipids and to what extent it affects the heat tolerance Since the hit1-1 allele is a point mutation leading to a Ser-to-Tyr amino acid substitution, 5 one may suspect that the temperature-sensitive phenotype of hit1-1 plants is produced by the thermolabile properties of the hit1-1 protein.…”

“…Nevertheless, because hit1-1 plants are more sensitive than wild-type to osmotic and saline stress inhibition during seedling germination and development, 4,5,7 it is unlikely that the heat-intolerant phenotype of hit1-1 is derived from a simple alternation in the thermal stability of a gene product. To answer this question and to provide further insight into the roles of HIT1 in plasma membrane acclimation to heat stress, electrophoretic patterns of plasma membrane proteins were analyzed.…”