Effect of salt, drought and mechanical wounding stress on gene expression and hormone profiles of Brachypodium distachyon

The rising world population with limited arable lands and the severe effect of climate change require an increase in crop yield. However, abiotic stress factors such as salinity, drought and mechanical wounding also decrease agricultural productivity. The development of crops that can cope with various environmental stress is the key to higher yield. Phytohormones and their cross-talk control many physiological and molecular mechanisms and mediate stress responses through activation of stress-responsive genes. Elucidation of stress-responsive genes and phytohormone signaling are crucial to contribute to a deeper understanding of their roles and relationship in complex response mechanisms of plants under stress. In this study, Brachypodium distachyon (Bd21 line), a powerful monocot model plant was used to determine the expression changes in multiple stress-responsive genes by quantitative real-time polymerase chain reaction (qRT-PCR) and quantify the hormonal changes via high-performance liquid chromatography (HPLC) under salinity, drought and time-dependent mechanical wounding stress including local and systemic events. From different gene families, 58 candidate multiple stress-responsive genes were identified by orthology analysis and in accordance with the literature, and eight of these genes were used for gene expression studies. EXPA2, GF14d, LOX3, P5CS1, PP2CA6 and WRKY36 genes were up-regulated under drought, salinity and wounding. Under salinity, all genes were up-regulated whereas under drought the genes rather than ERF1 and SUT2 were up-regulated. In response to wounding stress, the highest fold-changes were observed at 24th hour at wound sites compared to the gene expression levels at 0th and 6th hours. Besides, wound sites had higher gene expression levels than wound adjacent sites in general. On the other hand, in B. distachyon, salicylic acid (SA) levels under drought, and abscisic acid (ABA) levels under salinity and wounding stress showed increasing trends. Indole acetic acid (IAA) levels were significantly reduced at all stress conditions. Characterization and overexpression studies of determined genes can pave the way towards generating multiple stress-tolerant crops.