Insights Into the BR2/PGP1-mediated Patterns for Shoot and Root Growth in Maize Early Seedling Development by Comparative Transcriptome Sequencing

Abstract

Plant shoot and root growth is regulated by multiple factors, including the hormone auxin. A maize brachytic2 (br2) mutant displays a shortened shoot and root with high auxin concentration in their apexes, where BR2 encodes an auxin transporter P-glycoprotein1 (PGP1). We employed comparative transcriptome sequencing to explore the BR2/PGP1-mediated patterns for shoot and root growth among br2, wild type (WT), and hybrid F1 (br2 × WT). The results show 352 genes in the br2 shoot and 234 genes in the br2 root are differentially expressed compared to WT and F1. Zm00001d045203 and Zm00001d031562 were identified as two auxin-responsive genes in both the shoot and root. The Zm00001d045203 gene is down-regulated in br2 and encodes an Aux/IAA inhibitor involved in the SCFTIR1/AFB-mediated auxin signaling pathway. The up-regulated Zm00001d031562 gene encodes a small GTPase belonging to the Rab/Ypt family, which takes part in auxin-mediated responses in Arabidopsis. Cytology analysis reveals that reduced cell elongation affects the shoot and root growth of br2. The Zm00001d043477 gene is down-regulated and encodes a member of the cellulose synthase protein family, possibly reducing cell elongation in the br2 shoot and root. These results reveal the specific regulation of auxin actions and cell responses by BR2/PGP1.