Transcriptome analysis reveals the role of BpGH3.5 in root elongation of Betula platyphylla × B. pendula

Abstract

The GH3 family comprises a set of early auxin-responsive genes. Several previous studies have proven that GH3 family proteins play important roles in various aspects of plant growth and development. Our previous studies have found that the overexpression or suppression of BpGH3.5 in birch tree can result in shorter primary and lateral root compared to non-transgenic control, however, the molecular mechanism underlying is not clear. To further reveal the roles of BpGH3.5 in root elongation of birch (Betula platyphylla × B. pendula), we carried out transcriptome analysis on BpGH3.5-overexpressed (G1 and G5), BpGH3.5-suppressed (AG1), and non-transgenic (NT) birch. Compared with the NT line, 3,320 and 5,212 unigenes were found to be differentially expressed in the BpGH3.5 overexpressed and suppressed lines, respectively. Many differentially expressed unigenes related to cell proliferation and growth were downregulated in both the BpGH3.5-overexpressed and suppressed plants, which is consistent with the short-root phenotypes observed in these lines. We found that indole-3-acetic acid (IAA) biosynthesis and signaling pathways were affected in the BpGH3.5-overexpressed and suppressed plants. Interestingly, Free IAA levels were significantly lower in BpGH3.5-overexpressed and BpGH3.5-suppressed birch than in NT plants. This suggested that the expression levels of BpGH3.5 may play a role in maintaining the balance of free IAA in birch and the decreased IAA levels may be responsible for the short-root phenotype of the transgenic birch.