Integrative analysis of HD-Zip III gene PmHB1 contribute to the plant architecture in Prunus mume

Abstract Mei (Prunus mume) is a traditional fruit and ornamental woody plant. P. mume cultivars with dwarf and dense intersecting branched tree architecture are essential for enhancing the ornamental value and application diversity, such as bonsai, flower arrangement and potted plants. However, little is known about the mechanism of branching in P. mume. The apical meristem produces the organs of the above-ground part, which is essential for branch development. The HD-Zip III subfamily transcription factors influence the development of multiple lateral organs and meristem maintenance. However, their roles in regulating tree architecture have not been studied in P. mume. Here, the PmHB1 gene, encoding the HD-Zip III subfamily transcription factor, was strongly expressed in the hypocotyl, young leaf, root primordia, leaf bud, flower bud, style, and vascular tissues in leaf and inflorescence, which could respond to multiple plant hormones (such as GA3, IAA, ZA, KT, and BR). It is worth noting that there was a significant correlation between branch quantity and PmHB1 expression level in different mei cultivars. The formation of PmHB1 protein was controlled through the miR165/166 post-transcriptional regulation. Overexpression of the PmHB1 gene in Arabidopsis increased of the number of primary axillary inflorescence in leaf axil and secondary axillary inflorescence in the cauline leaf axil. The expression levels of genes involved in meristem maintenance (CLV3, RAP2.6 L, STM, BEL1, PEAR, WUS), auxin metabolism and signal transduction (IAA30, IAA20, PIN1, LAX3, LAX2, YUCCA5, TAA1, MP), cytokinin metabolism, and signaling transduction (IPT4, IPT7, ARR1, ARR2, MET1) were significantly changed in transgenic Arabidopsis. Moreover, according to yeast two-hybrid and bimolecular fluorescence complementation experiments, the transcription factor PmHB1 could interact with multiple proteins, such as Pm005033 (PmCSN5A), Pm005297 (PmHSFB4), Pm016138 (PmSPL13A), Pm024774 (PmEB1A), and Pm026192 (PmZPR4). Taken together, the PmHB1 gene could regulate the apical meristem development and promote the branching in P. mume.