ABSTRACT
Potato (Solanum tuberosum L.) periderm is composed of the meristematic phellogen that gives rise to an external layer of suberized phellem cells (the skin) and the internal parenchyma-like phelloderm. The continuous addition of new skin layers and the sloughing of old surface layers during tuber maturation results in smooth, shiny skin. However, smooth-skin varieties frequently develop unsightly russeting in response to high soil temperatures. Microscopic observation of microtubers exposed to high temperatures (37 degrees C) suggested heat-enhanced development and accumulation of suberized skin-cell layers. To identify the genes involved in the periderm response to heat stress, skin and phelloderm samples collected separately from immature tubers exposed to high soil temperatures (33 degrees C) and controls were subjected to transcriptome profiling using a potato cDNA array. As expected, the major functional group that was differentially expressed in both skin and phelloderm consisted of stress-related genes; however, while the major up-regulated phelloderm genes coded for heat-shock proteins, many of the skin's most up-regulated sequences were similar to genes involved in the development of protective/symbiotic membranes during plant-microbe interactions. The primary activities regulated by differentially expressed peridermal transcription factors were response to stress (33%) and cell proliferation and differentiation (28%), possibly reflecting the major processes occurring in the heat-treated periderm and implying the integrated activity of the stress response and tissue development. Accumulating data suggest that the periderm, a defensive tissue, responds to heat stress by enhancing the production and accumulation of periderm/skin layers to create a thick protective cover. Skin russeting may be an indirect outcome; upon continued expansion of the tuber, the inflexible skin cracks while new layers are produced below it, resulting in a rough skin texture.
Subject(s)
Gene Expression Profiling , Meristem/physiology , Solanum tuberosum/physiology , Gene Expression Regulation, Plant , Hot Temperature , Meristem/genetics , Oligonucleotide Array Sequence Analysis , Plant Proteins/genetics , Plant Proteins/metabolism , Solanum tuberosum/genetics , Stress, PhysiologicalABSTRACT
The rind of fruits of muskmelon (Cucumis melo L. var. reticulatus) contains a network of suberized tissue referred to as the 'netting', and peroxidase (EC 1.11.1.7) activity is necessary to the polymerization of the aromatic domain of suberin. Peroxidase activity increased dramatically during the early stages of melon fruit netting, and in fruits exhibiting incomplete netting, peroxidase activity was significantly higher in netted than in non-netted regions of the same fruit. Moreover, analysis of peroxidase activity in three varieties of smooth-rind melons (Cucumis melo var. inodorous) indicated lower levels of the activity in rind samples, taken throughout fruit development, than in rinds of netted varieties. Netting-associated anionic peroxidase (NAPOD) was isolated from the melon rind at an early stage of netting development, partially purified, microsequenced and its cDNA was cloned. It was found to be a single-copy gene within the genome of netted and smooth melon varieties, and highly homologous to other Cucurbitaceous anionic peroxidases. A high transcript level was only detected in the rind of the netted variety. Monitoring the gene expression of netting-associated anionic peroxidase, together with other enzymes involved in the netting will shed light on the molecular control of the suberization processes in the melon rind and in plants in general.
