The cDNA Structures and Expression Profile of the Ascorbate Peroxidase Gene Family During Drought Stress in Wild Watermelon

Abstract

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.

Genome-Wide Characterization of Ascorbate Peroxidase Gene Family in Peanut (Arachis hypogea L.) Revealed Their Crucial Role in Growth and Multiple Stress Tolerance

“…Recent studies show that the cis-elements in APX genes contribute to the plant abiotic and phytohormones stress responses. Similar types of abiotic and phytohormone-related cis-regulatory elements have been identified in previous studies (Akbudak et al, 2018;Malambane et al, 2018;Tao et al, 2018;Liao et al, 2020;Tyagi et al, 2020;Wang et al, 2022). Furthermore, AhAPXs gene functions were further predicted by GO enrichment analysis (Figure 10), which also supported the role of these genes in ROS scavenging and stress response mechanisms.…”

“…Previous studies showed that APX family genes are usually clustered into four major groups based on their subcellular localization or tree topologies (Pandey et al, 2011;Malambane et al, 2018;Tyagi et al, 2020). In the present study, all APX genes from four plant species were grouped into 11 main groups based on tree topologies and sequence similarities (Figure 2).…”

“…Usually, APX gene family of plants comprises a few genes. In this study, 166 AhAPX genes have been discovered in peanut genome (Supplementary Table 10), a larger APX family than previously reported APX gene families in watermelon (Malambane et al, 2018), shrub (Wang et al, 2022), rice (Teixeira et al, 2004), A. thaliana (Panchuk et al, 2002, Panchuk et al, 2005, sorghum (Akbudak et al, 2018), kiwifruit (Liao et al, 2020), tomato (Najami et al, 2008), wheat (Tyagi et al, 2020), and cotton (Tao et al, 2018). Deviations in the APX members amongst diverse plant species may perhaps be attributed to gene duplication events involving tandem and segmental repeats and play a role in expanding APXs for deviation.…”

“…Additionally, APX enzymes are automated by APX gene family involved in stress tolerance has been thoroughly explored in diverse plant species using various in silico approaches. For example, five APX genes have been discovered in wild watermelon (Citrullus lanatus) (Malambane et al, 2018); six in shrub (Ammopiptanthus nanus) (Wang et al, 2022); eight in rice (Oryza sativa L.) (Teixeira et al, 2004) and Arabidopsis thaliana (Panchuk et al, 2002, Panchuk et al, 2005; nine in sorghum (Sorghum bicolor L.) (Akbudak et al, 2018); 13 in kiwifruit (Actinidia chinensis) (Liao et al, 2020); 16 APX genes in tomato (Solanum lycopersicum L.) (Najami et al, 2008); 21 in wheat (Triticum aestivum L.) (Tyagi et al, 2020); and 26 in cotton (Gossypium hirsutum L.) (Tao et al, 2018). Nevertheless, the APX gene family in peanut (Arachis hypogea L.) has not been systematically reported, and their roles in peanut development and stress tolerance still remain ambiguous.…”

Comparative Transcriptome and Weighted Gene Co-expression Network Analysis Identify Key Transcription Factors of Rosa chinensis ‘Old Blush’ After Exposure to a Gradual Drought Stress Followed by Recovery

“…In this study, two genes encoding APX were up-regulated and four were down-regulated. Similarly, in the study of Citrullus lanatus, the changes of APX genes are different under drought stress (Goitseone et al, 2018). The post-harvest petals of cut rose (Rosa hybrida cv.…”