Six peroxidase (POD) cDNAs were isolated from suspension cultures of sweetpotato (Ipomoea batatas) by cDNA library screening, and their expression was investigated with a view to understanding the physiological functions of each POD in relation to environmental stress. The gene products encoded by these cDNAs could be divided into two groups, anionic PODs (SWPA4, SWPA5, SWPA6) and basic PODs (SWPB1, SWPB2, SWPB3), on the basis of the predicted pI values of the mature proteins. RT-PCR analysis revealed that the six POD genes showed diverse expression patterns in various tissues of intact plants, a various stages of growth in suspension cultures, and in leaf tissues exposed to different stresses. The six genes from which they were derived are predominantly expressed in cultured cells of sweetpotato. Thus, transcripts of swpa4 were not detected in any tissues of the intact plant. The genes swpa6 and swpb1 were highly expressed in root tissues, whereas swpa6 and swpb3 were highly expressed in stem tissues. During suspension culture, the expression patterns of the six genes differed from each other. The level of swpa4, swpa5, swpb2 and swpb3 transcripts progressively increased during culture, whereas swpa6 and swpb1 showed high expression levels regardless of the age of the culture. In leaf tissues the six POD genes responded differently to various abiotic stresses. In particular, swpa4 was highly induced by several abiotic stresses, including exposure to hydrogen peroxide (440 mM) or NaCl (100 mM), and wounding of leaf tissues, suggesting that this POD gene is inducible by many stresses. Based on the different expression patterns of these POD genes, we propose that each POD may have different enzymatic properties and physiological functions during cell growth and development.
Mapping enhancers to genes is a fundamental goal of modern biology. We have developed an innovative strategy that maps enhancers to genes in a principled manner. We illustrate its power by applying it to Myrf . Despite being a master regulator of oligodendrocytes, oligodendrocyte enhancers governing Myrf expression remain elusive. Since chromatin conformation capture studies have shown that a gene and its enhancer tend to be found in the same topologically associating domain (TAD), we started with the delineation of the Myrf TAD. A genome-wide map of putative oligodendrocyte enhancers uncovered 6 putative oligodendrocyte enhancers in the Myrf TAD, narrowing down the search space for Myrf enhancers from the entire genome to 6 loci in a principled manner. Epigenome editing experiments revealed that two of them govern Myrf expression for oligodendrocyte development. Our new method is simple, principled, and powerful, providing a systematic way to find enhancers that regulate the expression of a gene of interest. Since it can be applied to most cell types, it would greatly facilitate our effort to unravel transcriptional regulatory networks of diverse cell types.
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