Small heat shock proteins regulate growth and development in tomato (Solanum lycopersicum)
Abstract
Fruit ripening is a genetically regulated process involving well orchestrated chemical and structural changes giving the ripe fruit its desirable characteristics including color, texture, flavor and aroma. Environmental stresses, especially temperature above 30°C, impair both fruit set and ripening. Our laboratory has previously characterized a novel small heat shock protein (sHSP), designated as VISCOSITY1 (VIS1) whose endogenous expression patterns were correlated with juice quality attributes. I have characterized effects of VIS1 on growth and development of tomato under greenhouse and field conditions using transgenic plants constitutively expressing sense (OS) - and antisense (OA) genes of VIS1. Four hour incubation at 35, 40 and 45°C followed by 7 days growth in greenhouse, VIS1-OS tomato seedlings exhibited significant increases in fresh and dry weights compared to wild-type seedlings when exposed to heat shock whereas VIS1-OA seedlings showed comparable growth to wild-type seedlings at all temperatures tested. Maximum increase in growth of VIS1-OS seedlings was observed after exposure at 35°C. Similar trends were observed when VIS1-OS seedlings were gradually exposed to higher temperatures, but increase was less pronounced than those obtained after heat shock at the same temperatures. VIS1-OA seedlings showed a significant decrease in fresh and dry weight gain after gradual exposure to higher temperatures. Under field conditions, VIS1-OS plants did not exhibit significant increase in fresh and dry weights but the VIS1-OA plants showed decreased growth throughout plant lifecycle. VIS1-OS plants showed a change in the architecture of flower clusters from simple to dichotymously branched cyme and increase in the number of flowers. Fruit ripening was delayed in VIS1-OS plants, while early ripening were observed in plants expressing antisense VIS1. Recombinant VIS1 protected malate dehydrogenase from thermal aggregation at 45°C indicating its chaperone activity. VIS1-OS seedlings showed higher amino acid uptake and in vivo protein synthesis under heat stress suggesting a role for VIS1 in maintaining cellular vitality. Transgenic plants over-expressing other sHSPs (chloroplast-specific sHSP with and without transit peptide and mitochondrial-specific sHSP) were developed. Preliminary characterization of lines homozygous for these transgenes implied a role in ripening for these sHSPs. Taken together my results provide strong evidences that VIS1 in particular and sHSPs in general play significant roles in plant growth and development both under normal and high temperature growth conditions.
Degree
Ph.D.
Advisors
Handa, Purdue University.
Subject Area
Molecular biology|Horticulture
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