Emerging functions of chromatin modifications in auxin biosynthesis in response to environmental alterations

Auxin is one of the most important hormone groups in plants. It has been documented to play various functions in plant growth and development. In this phytohormone group, indole-3-acetic acid (IAA) is widely considered as a main natural auxin. To date, many lines of evidence have revealed that the alterations of ambient environment such as light and temperature conditions can affect the IAA biosynthesis which consequently redirects the growth and development of the plants so that they can adapt to the new environmental conditions. Current studies have shown the large impact of chromatin modifications in the regulation of eukaryotic gene expression. Previous studies have elucidated different epigenetic factors in the regulation of auxin signaling pathway in the plants. This review aimed to provide a precise and systemic overview of the chromatin modifications at the auxin biosynthesis gene loci, namely YUCCA (YUC) genes, and their effects on the expression of these genes. Based on these emerging data, we propose different hypothetical models demonstrating the functions of epigenetic factors as well as chromatin modifications in the regulation of YUC genes which can subsequently determine the auxin accumulation in the plants.