Recently, the polyploid team of Nanjing Agricultural University published a research article on PNAS entitled”DNA hypomethylation in tetraploid rice potentiates stress-responsive gene expression for salt tolerance”. DNA methylation and transcription levels reveal how genome polyploidy enhances rice’s ability to adapt to salt stress environments.
Genome polyploidization (double doubling of the whole genome) is common in the evolution of plants. Many plants, including important crops, are polyploid, such as hexaploid wheat, tetraploid cotton and potatoes. Although crops such as rice, soybeans, and corn are diploid, they have also experienced at least one genome-wide doubling event during their evolution. Studies have shown that multiplying the genome will enhance the adaptation of plants to unfavorable environments and expand their range of survival. The doubling of the whole genome will also cause changes in epigenetic modifications and transcription levels. However, how these changes enhance the ability of plants to adapt to stress environments remains unclear.
This study found that compared with diploid rice, tetraploid rice reduces the absorption of sodium ions and has a stronger ability to survive in salt stress environments. In tetraploid rice, many sites in the genome, including genes related to stress, have decreased DNA methylation levels (Figure 1A). After salt treatment, the hypomethylation state causes the salt stress-related genes (jasmonic acid synthesis and signal transduction genes, etc.) in tetraploid rice to be activated more significantly (Figure 1B), accumulating more jasmonic acid-isoleucine acid. At the same time, the activation of stress-related genes in tetraploid rice will induce the activation of adjacent transposons, which will increase the methylation level of the transposon region to inhibit the transposon and maintain the stability of the genome (Figure 1B). The decrease of DNA methylation level after quadrupling strengthens the response to stress, while the increase of methylation level after stress inhibits the expression of transposons and adjacent genes related to stress. This feedback regulation enhances the adaptability of tetraploid rice to salt stress. After the salt stress is removed, the tetraploid rice will partially recover its hypomethylation state (compared to the diploid) (Figure 1C). When exposed to salt again, the activation of stress-related genes in tetraploid rice was still significantly higher than that in diploid rice (Figure 1D). Moreover, the two different tetraploid rices all present this regulation mechanism of DNA methylation and stress-related gene expression, indicating its universality.
This study analyzed the epigenetic mechanism of polyploid rice to enhance salt tolerance for the first time, and provided a new molecular mechanism for polyploid species to enhance environmental adaptability during evolution. Longfei Wang, a PhD student at Nanjing Agricultural University, is the first author of the article, Z. Jeffrey Chen, a professor at the University of Texas at Austin and adjunct professor of Nannong, is the corresponding author of the paper, Fangjie Zhao from the School of Resources and Environmental Sciences, Nanjing Agricultural University, and Qingxin Song from the School of Agriculture Professors, doctoral students Cao Shuai, Wang Peitong and Lu Kening are co-authors.
For details, please refer to the article link:https://www.pnas.org/content/118/13/e2023981118