Mitochondrial biogenesis as revealed by mitochondrial transcript profiles during germination and early seedling growth in wheat

Abstract

Germination of imbibed embryos is the initial stage of plant development that is accompanied by the burst of mitochondrial respiration. To understand the process of mitochondrial biogenesis during this critical stage in wheat development, we monitored changes in mitochondrial transcript profiles during the first 3 days by adopting a newly devised macroarray system. The whole experiment was conducted in the dark to avoid influences of photosynthesis. Dry quiescent embryos started respiration rapidly after imbibition and the rate of oxygen uptake increased to peak at the first day followed by a continuous decrease until the third day under this condition. Both the cytochrome and alternative electron transport pathways appeared to contribute to this initial burst. Shoot and root growth was also remarkable during this period. Mitochondrial transcriptome was studied by macroarray analysis using 28 mitochondrial protein-coding genes, 4 nuclear encoded mitochondria-targeted genes and 2 nuclear genes as control. All transcripts were present in dry embryos at different initial levels, and a large variability was observed in their abundance among individual genes throughout the tested period. Gene expression was categorized into four clusters according to the profiles of individual transcript accumulation. A majority of the genes encoding subunits of the respiratory complexes belonged to two major clusters, the time course of transcript accumulation of one cluster agreeing with that of respiratory development and the other remaining at high constant levels. The macroarray system devised in this study should be useful in monitoring mitochondrial biogenesis under various growth conditions and at different developmental stages in cereals.

Profiling of mitochondrial transcriptome in germinating wheat embryos and seedlings subjected to cold, salinity and osmotic stresses

“…4). A similar situation was found also under normal conditions (Khanam et al, 2007). With respect to another polycistronic unit of nad6-nad1 in wheat (Haouazine et al, 1993), nad6 transcript showed decreases by all three stresses but nad1 transcript decreased mainly by low temperature stress.…”

“…low temperature, high salinity and high osmotic potential were applied to germinating embryos after imbibition and seedlings. Imbibition and sterilization of seeds were performed according to Khanam et al (2007). For low temperature stress, imbibed seeds were placed on filter paper containing 0.1% Hyponex (N-P-K = 5-10-5, Hyponex, Osaka, Japan) solution in the dark at 4°C for 1 to 3 days.…”

“…We also selected 4 nuclear encoded and mitochondriatargeted wheat genes (Whlp, TaMRPL5, TaMRPL11 and Mn-SOD) plus wheat Ubiquitin and Actin genes as controls. Primer sequences, preparation of membrane filters and all other steps including RNA isolation, reverse transcription, hybridization, washing, signal detection and data analysis were as described in Khanam et al (2007). RNA labeling was repeated twice using independently isolated total RNA samples, and hybridization was carried out twice with independently prepared membrane filters.…”

“…Macroarray analysis of mitochondrial gene expression under stress conditions We previously developed a macroarray system to study mitochondrial biogenesis by monitoring the level of mitochondrial transcripts in developing wheat seedlings under normal growth conditions (Khanam et al, 2007). We now attempted to apply this system to the stress conditions.…”

“…Our aim was to study possible effect of cold, high salinity and osmotic stresses on mitochondrial development and function during germination and early seedling growth. For this we performed macroarray analysis using a set of 28 mitochondrial genes and 5 nuclear-encoded and mitochondria-targeted genes (Khanam et al, 2007). We pursued two particular objectives: 1) to identify mRNAs that change in abundance in a "stress-specific" fashion, and 2) to identify mRNAs that are co-regulated and exhibit a "shared stress" response during the early growth phase, i.e.…”