Ascorbate peroxidase (APX) plays an important role in detoxifying reactive oxygen species under environmental stress. Although previous work in drought-tolerant wild watermelon has shown an increase in chloroplast APX enzyme activity under drought, molecular entities of APX have remained uncharacterized. In this study, structure and transcriptional regulation of the APX gene family in watermelon were characterized. Five APX genes, designated as CLAPX1 to CLAPX5, were identified from watermelon genome. The mRNA alternative splicing was suggested for CLAPX5, which generated two distinct deduced amino acid sequences at their C-terminus, in resemblance to a reported alternative splicing of chloroplast APXs in pumpkin. This observation suggests that two isoenzymes for stromal and thylakoid-bound APXs may be generated from the CLAPX5 gene. Phylogenetic analysis classified CLAPX isoenzymes into three clades, i.e., chloroplast, microbody, and cytosolic. Physiological analyses of wild watermelon under drought showed a decline in stomatal conductance and CO 2 assimilation rate, and a significant increase in the enzyme activities of both chloroplast and cytosolic APXs. Profiles of mRNA abundance during drought were markedly different among CLAPX genes, suggesting distinct transcriptional regulation for the APX isoenzymes. Up-regulation of CLAPX5-I and CLAPX5-II was observed at the early phase of drought stress, which was temporally correlated with the observed increase in chloroplast APX enzyme activity, suggesting that transcriptional up-regulation of the CLAPX5 gene may contribute to the fortification of chloroplast APX activity under drought. Our study has provided an insight into the functional significance of the CLAPX gene family in the drought tolerance mechanism in this plant.
Ethylene (CH), a phytohormone that is produced in response to both abiotic and biotic stresses, is an important factor influencing the efficiency of Agrobacterium-mediated transformation. In this study, effects of various ethylene inhibitors on the efficiency of Agrobacterium-mediated genetic transformation in drought-tolerant wild watermelon was comparatively examined. Consequently, in comparison to the application of chemical inhibitors such as AgNO and aminoethoxyvinylglycine (AVG), lower ethylene level was observed when the infecting Agrobacterium contained a gene for 1-aminocyclopropane-carboxylic acid (ACC) deaminase (acdS), which cleaves ethylene precursor ACC into α-ketobutyrate and ammonia. GUS histochemical and spectrophotometric enzyme assays showed that acdS was more effective in enhancing gene transfer than the chemical ethylene inhibitors. Efficiency of transgenic shoots formation was higher in acdS- and AVG-treated explants. These observations demonstrated that controlling the ethylene level during co-cultivation and shoot formation, particularly using the acdS-harboring Agrobacterium, is advantageous for enhancing the transformation efficiency in this plant.
Information on genetic variation is very important for finger millet breeding program. The objective of this study was to evaluate the extent of genetic variation in finger millet accessions. Eighty two accessions were evaluated in the dry season 2010/11 and the rainy season 2011 at Khon Kaen University, Thailand, and also evaluated in Botswana College of Agriculture in Botswana in rainy season in 2013. The results of combined analysis of variance for mean data of traits studied revealed highly significant variation for most of the traits studied. High variations were observed for yield per plant with a range of 15 g-144 g per plant while low variations were observed for fingers per panicle with a range of 5-11 fingers per panicle. Qualitative traits like seed colors showed high variation with six different colors observed during the study 2,2,4, 49, 8 and 17 accessions had white, light brown, brown, ragi brown, red and purple seed colors, respectively. A dendrogram constructed using the qualitative traits revealed high variation, separated the wild accessions (IE 4709) from the cultivated accessions, then grouped the cultivated accessions into 5 main groups at 86% similarity level. Genetic variation evaluation based on morphological characters has proved to be very informative and can also be manipulated into selecting superior accessions to be utilized as parents for a breeding program.
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