PNNL

Abstract

Sorghum (Sorghum bicolor (L.) Moench) is an important cereal crop noted for its ability to survive water-limiting conditions. Herein, we explore the changes in histone modifications through developmental stages and in response to drought stress in two sorghum genotypes. Top-down mass spectrometry (MS) is an ideal method to profile histone modifications and distinguish closely related histone proteoforms. We analyzed leaves of 48 plants and identified 26 unique histone proteins and 677 unique histone proteoforms (124 full-length and 553 truncated proteoforms). We detected trimethylation on nearly all H2B N-termini where acetylation is commonly expected. In addition, an unexpected modification on H2A histones was assigned to N-pyruvic acid 2-iminylation based on its unique neutral loss of CO2. Interestingly, some of the truncated histones, in particular H4 and H3.2, showed significant changes that correlated with the growth conditions. The histone proteoforms could serve as targets in search of chromatin modifiers and ultimately have important ramifications for attempts at epigenetic reprogramming in plants.