Chromatin-Level Differences Elucidate Potential Determinants of Contrasting Levels of Cold Sensitivity in Maize Lines

Maize is a subtropical, cold-sensitive species. However, some varieties of this species have the potential to withstand long-term low temperatures, even at the seedling stage. The molecular basis of this phenomenon has not been determined. In a chromatin-level study, we compared the cold-stress reaction of seedlings of two maize inbred lines showing contrasting levels of cold sensitivity. The cold-tolerant line was selected based on field data and previous physiological and transcriptomic level studies. The first condition of gene expression-chromatin accessibility-was assessed by formaldehyde-aided isolation of regulatory elements method and DNA sequencing. Potentially expressed genes andcis-regulatory sequences open for interaction with transcription factors have been defined. The results of this study suggest that during cold stress, the tolerant maize line shifted resources from growth to defense. This shift was shown by potential hormone-level events-degradation of growth-promoting gibberellins and synthesis of jasmonic and abscisic acids. This finding is congruent with the xeromorphic morphology of seedlings of the cold-tolerant line and their ability to regrow when stress ceases. It is a common reaction of cold-tolerant maize lines. Moreover, in the cold-tolerant line, several genes from the low-temperature signaling pathways were potentially expressed. Additionally, numerous stress-response AP2/EREBP-bindingcis-motifs were accessible in the cold-tolerant line. Differently in the cold-sensitive B73 line, MADS-bindingcis-motifs were the most abundant. Development of the photosynthetic apparatus is crucial for the survival of maize seedlings at low temperature. Our results suggest efficient photosynthesis in seedlings of the cold-tolerant line, as was described earlier in physiological-level analyses.

Automated summary

Maize is a subtropical, cold-sensitive species, but some varieties have the ability to withstand low temperatures. A study on cold-tolerant maize lines revealed resource shifting from growth to defense during cold stress, along with changes in hormone levels and potential gene expressions related to low-temperature signaling pathways. Additionally, differences were observed in accessible cis-regulatory motifs between cold-tolerant and cold-sensitive maize lines, with the former showing abundance in stress-response AP2/EREBP-binding motifs.