Genome-Wide Identification and Expression Analysis of Growth-Regulating Factors in <i>Eucommia ulmoides</i> Oliver (Du-Zhong)

The roots, stems, leaves, and seeds of <i>Eucommia ulmoides</i> contain a large amount of trans-polyisoprene (also known as Eu-rubber), which is considered to be an important laticiferous plant with valuable industrial applications. Eu-rubber used in industry is mainly extracted from leaves. Therefore, it is of great significance to identify genes related to regulating the leaf size of <i>E. ulmoides</i>. Plant growth-regulating factors (GRFs) play important roles in regulating leaf size, and their functions are highly conserved across different plant species. However, there have been very limited reports on EuGRFs until now. In this study, eight canonical EuGRFs with both QLQ and WRC domains and two putative eul-miR396s were identified in the chromosome-level genome of <i>E. ulmoides</i>. It is found that, unlike AtGRFs, all EuGRFs contain the miR396s binding site in the terminal of WRC domains. These <i>EuGRFs</i> were distributed on six chromosomes in the genome of <i>E. ulmoides</i>. Collinearity analysis of the <i>E. ulmoides</i> genome revealed that <i>EuGRF1</i> and <i>EuGRF3</i> exhibit collinear relationships with <i>EuGRF2</i>, suggesting that those three genes may have emerged via gene replication events. The collinear relationship between <i>EuGRFs</i>, <i>AtGRFs</i>, and <i>OsGRFs</i> showed that <i>EuGRF5</i> and <i>EuGRF8</i> had no collinear members in <i>Arabidopsis</i> and rice. Almost all <i>EuGRFs</i> show a higher expression level in growing and developing tissues, and most <i>EuGRF</i> promoters process phytohormone-response and stress-induced cis-elements. Moreover, we found the expression of <i>EuGRFs</i> was significantly induced by gibberellins (GA₃) in three hours, and the height of <i>E. ulmoides</i> seedlings was significantly increased one week after GA₃ treatment. The findings in this study provide potential candidate genes for further research and lay the foundation for further exploring the molecular mechanism underlying <i>E. ulmoides</i> development in response to GA₃.