Dynamic Alternations in Cellular and Molecular Components during Blossom-End Rot Development in Tomatoes Expressing sCAX1, a Constitutively Active Ca2+/H+ Antiporter from Arabidopsis

Sergio Tonetto De Freitas,Elizabeth J Mitcham,Sunghun Park,Qingyu Wu,Malkeet Padda

doi:10.1104/pp.111.175208

Sergio Tonetto De Freitas, Elizabeth J Mitcham + Show 3 more

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https://doi.org/10.1104/pp.111.175208

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Abstract

Although calcium (Ca) concentration in cellular compartments has been suggested to be tightly regulated, Ca deficiency disorders such as blossom-end rot (BER) in tomato (Solanum lycopersicum) fruit may be induced by abnormal regulation of Ca partitioning and distribution in the cell. The objectives of this work were to analyze the effects of high expression of the constitutively functional Arabidopsis (Arabidopsis thaliana) Ca(2+)/H(+) exchanger (sCAX1) tonoplast protein in tomato fruit on cellular Ca partitioning and distribution, membrane integrity, and the transcriptional profile of genes potentially involved in BER development. Wild-type and sCAX1-expressing tomato plants were grown in a greenhouse. Wild-type plants did not develop BER, whereas sCAX1-expressing plants reached 100% BER incidence at 15 d after pollination. The sCAX1-expressing fruit pericarp had higher total tissue and water-soluble Ca concentrations, lower apoplastic and cytosolic Ca concentrations, higher membrane leakage, and Ca accumulation in the vacuole of sCAX1-expressing cells. Microarray analysis of healthy sCAX1-expressing fruit tissue indicated down-regulation of genes potentially involved in BER development, such as genes involved in membrane structure and repair and cytoskeleton metabolism, as well as up-regulation of genes that may have limited BER damage expansion, such as genes coding for heat shock proteins, glutathione S-transferases, and peroxidases. The results indicate that the high expression of the sCAX1 gene reduces cytosolic and apoplastic Ca concentrations, affecting plasma membrane structure and leading to BER symptom development in the fruit tissue.

Highlights

Calcium (Ca) concentration in cellular compartments has been suggested to be tightly regulated, Ca deficiency disorders such as blossom-end rot (BER) in tomato (Solanum lycopersicum) fruit may be induced by abnormal regulation of Ca partitioning and distribution in the cell
The apoplastic Ca concentration must be greater than 0.1 mM Ca to maintain the integrity and selectivity of the plasma membrane, cytosolic Ca concentration must be maintained in the range of 0.1 to 0.2 mM to avoid toxicity, and Ca storage organelles must contain 1 to 10 mM Ca, which is required for signaling responses and charge balance (Hanson, 1960; Plieth, 2001; White and Broadley, 2003)
This assumption is based on the facts that (1) growing tomato plants under hydroponic conditions with low Ca results in BER development, (2) fruit with BER symptoms usually have lower Ca concentrations, and (3) spraying fruit and plants with Ca solutions reduces the probability of BER development (Evans and Troxler, 1953; Geraldson, 1957; Millikan et al, 1971)

Summary

Introduction

Calcium (Ca) concentration in cellular compartments has been suggested to be tightly regulated, Ca deficiency disorders such as blossom-end rot (BER) in tomato (Solanum lycopersicum) fruit may be induced by abnormal regulation of Ca partitioning and distribution in the cell. The objectives of this work were to analyze the effects of high expression of the constitutively functional Arabidopsis (Arabidopsis thaliana) Ca2+/H+ exchanger (sCAX1) tonoplast protein in tomato fruit on cellular Ca partitioning and distribution, membrane integrity, and the transcriptional profile of genes potentially involved in BER development. The results indicate that the high expression of the sCAX1 gene reduces cytosolic and apoplastic Ca concentrations, affecting plasma membrane structure and leading to BER symptom development in the fruit tissue. Previous reports suggest that aberrant regulation of cellular Ca partitioning and distribution may lead to Ca deficiency symptom development (Hirschi, 1999; Ho and White, 2005) In these studies, high expression of a constitutively functional Arabidopsis. Since BER symptoms start with leaky membranes and cell plasmolysis (Ho and White, 2005), an abnormal depletion of the apoplastic pool of Ca in fruit tissue could explain the high incidence of BER observed in sCAX1-expressing fruit

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