AtVAM3 is Required for Normal Specification of Idioblasts, Myrosin Cells

Abstract

Myrosin cells in Capparales plants are idioblasts that accumulate thioglucoside glucohydrolase (TGG, also called myrosinase), which hydrolyzes glucosinolates to produce toxic compounds for repelling pests. Here, we show that AtVAM3 is involved in development of myrosin cells. It has been shown that yeast VAM3 is a Q(a)-SNARE that is involved in vesicle transport of vacuolar proteins and vacuolar assembly. We found that two Arabidopsis atvam3 alleles, atvam3-3 and atvam3-4/ssm, accumulate large amounts of TGG1 and TGG2 that are enzymatically active. An immunogold analysis revealed that TGGs were specifically localized in the vacuole of myrosin cells in atvam3 mutants. This result indicates that TGGs are normally transported to vacuoles in these mutants and that AtVAM3 is not essential for vacuolar transport of the proteins. We developed a staining method with Coomassie brilliant blue that detects myrosin cells in whole leaves by their high TGG content. This method showed that atvam3 leaves have a larger number of myrosin cells than do wild-type leaves. Myrosin cells were scattered along leaf veins in wild-type leaves, while they were abnormally distributed in atvam3 leaves. The mutants developed a network of myrosin cells throughout the leaves: myrosin cells were not only distributed continuously along leaf veins, but were also observed independent of leaf veins. The excess of myrosin cells in atvam3 mutants might be responsible for the abnormal abundance of TGGs and the reduction of elongation of inflorescence stems and leaves in these mutants. Our results suggest that AtVAM3 has a plant-specific function in development of myrosin cells.

The role of vacuole in plant cell death

“…2,3 Most vacuolar soluble proteins are synthesized on the endoplasmic reticulum as larger precursors and then transported into vacuoles, where precursor proteins are converted into their respective mature forms by vacuolar processing enzyme (VPE). [4][5][6][7][8] The machinery in plant cells is used to accumulate a variety of proteins in both types of vacuoles, hydrolytic enzymes including aspartate proteinases, 9 cysteine proteinases, 10,11 and nucleases 12 required for non-selective degradation of cellular components during programmed cell death (PCD), and defense proteins including pathogenesisrelated proteins (PR proteins), 13 myrosinases, 14 toxic proteins, 15 and lectins 16,17 for defense against invading pathogens.…”

A SNARE Complex Unique to Seed Plants Is Required for Protein Storage Vacuole Biogenesis and Seed Development ofArabidopsis thaliana

“…Why the vamp727 syp22-1 embryo exhibits chlorosis would be an interesting question to examine in a future study. gametogenesis, and development (Lukowitz et al, 1996;Leyman et al, 1999;Sanderfoot et al, 2001b;Kato et al, 2002;Zhu et al, 2002;Collins et al, 2003;Nuhse et al, 2003;Surpin et al, 2003;Yano et al, 2003;Ohtomo et al, 2005;Leshem et al, 2006;Ueda et al, 2006). These lines of evidence clearly indicate that SNAREdependent membrane fusion is an essential process to fulfill higher-order plant functions as well as for basic cellular activity.…”

Specialized Roles of the Conserved Subunit OST3/6 of the Oligosaccharyltransferase Complex in Innate Immunity and Tolerance to Abiotic Stresses

“…Protein gel blots were blocked in phosphate-buffered saline containing 0.1% (v/v) Tween 20 and 3% (w/v) bovine serum albumin. The membranes were probed with anti-horseradish peroxidase (HRP; Strasser et al, 2004), anti-PDI (Farid et al, 2011), anti-TGG2 (Ueda et al, 2006; kindly provided by Ikuko Hara-Nishimura), and anti-KOR1 antibodies (generated by immunization of rabbits with a synthetic peptide CSGEEEATGKIDKNT; Genscript). Endo H (New England Biolabs) and PNGase F (New England Biolabs) digestions were done as described in detail recently (Liebminger et al, 2012).…”