Genome-wide identification of the AlkB homologs gene family, PagALKBH9B and PagALKBH10B regulated salt stress response in Populus

Abstract

The AlkB homologs (<i>ALKBH</i>) gene family regulates N⁶-methyladenosine (m⁶A) RNA methylation and is involved in plant growth and the abiotic stress response. Poplar is an important model plant for studying perennial woody plants. Poplars typically have a long juvenile period of 7-10 years, requiring long periods of time for studies of flowering or mature wood properties. Consequently, functional studies of the <i>ALKBH</i> genes in <i>Populus</i> species have been limited. Based on <i>AtALKBHs</i> sequence similarity with <i>Arabidopsis thaliana</i>, 23 <i>PagALKBHs</i> were identified in the genome of the poplar 84K hybrid genotype (<i>P. alba</i> × <i>P. tremula</i> var. <i>glandulosa</i>), and gene structures and conserved domains were confirmed between homologs. The PagALKBH proteins were classified into six groups based on conserved sequence compared with human, Arabidopsis, maize, rice, wheat, tomato, barley, and grape. All homologs of <i>PagALKBHs</i> were tissue-specific; most were highly expressed in leaves. ALKBH9B and ALKBH10B are m⁶A demethylases and overexpression of their homologs <i>PagALKBH9B</i> and <i>PagALKBH10B</i> reduced m⁶A RNA methylation in transgenic lines. The number of adventitious roots and the biomass accumulation of transgenic lines decreased compared with WT. Therefore, <i>PagALKBH9B</i> and <i>PagALKBH10B</i> mediate m⁶A RNA demethylation and play a regulatory role in poplar growth and development. Overexpression of <i>PagALKBH9B</i> and <i>PagALKBH10B</i> can reduce the accumulation of H₂O₂ and oxidative damage by increasing the activities of SOD, POD, and CAT, and enhancing protection for Chl a/b, thereby increasing the salt tolerance of transgenic lines. However, overexpression lines were more sensitive to drought stress due to reduced proline content. This research revealed comprehensive information about the <i>PagALKBH</i> gene family and their roles in growth and development and responsing to salt stress of poplar.