High temperature stress disrupts genome methylation distinctively affects microspore abortion and anther indehiscence

DNA methylation regulates gene expression without changing the original DNA sequence, which regulates a range of functions in plant development and stress responses, maintenance genomic stability, stress response, and among others, but a role in male sterility under HT remains undetermined. In our previous studies, male sterility under high temperature is a critical factor contributing to yield loss in cotton. Using genome-wide total DNA methylation rate measurement by HPLC at three anther developmental stages under normal and high temperature (HT) conditions, we found that the total DNA methylation level of H05 was always lower than that in 84021 under HT, which was in accordance with more differentially expressed genes in H05 than in 84021 under HT (Min et al., 2014). To better understand how DNA methylation addresses HT stress during male reproductive stages, we performed whole genome bisulfite sequencing. Global disruption of DNA methylation, especially CHH methylation (where H=A, C or T), was found in an HT-sensitive line. Changes of 24-nucleotide small interference RNAs were significantly associated with DNA methylation levels. Experimental suppression of DNA methylation led to pollen sterility in the HT-sensitive line under NT, but did not affect the normal dehiscence of anther wall. Further transcriptome analysis of the anther showed that the expression of genes in sugar and reactive oxygen species (ROS) metabolic pathways were modulated significantly, but auxin biosynthesis and signaling pathways were slightly changed, indicating that HT disorders sugar and ROS metabolism via disrupting DNA methylation, leading to microspores sterility. This study opens up a path to create HT-tolerant cultivars using epigenetic solutions.