A basic/helix–loop–helix transcription factor controls leaf shape by regulating auxin signaling in apple

Abstract

Climate-driven phenological change across local spatial gradients leads to leaf shape variation. At higher elevations, leaves of broadleaf species tend to become narrower, but the underlying molecular mechanism is largely unknown. In this study, a series of morphometric analyses and biochemical assays, combined with functional identification in apple, were performed. We show that the decrease in apple leaf width with increasing altitude is controlled by a basic/helix-loop-helix transcription factor (bHLH TF), MdbHLH3. The MdbHLH3-overexpressing lines have a lower transcript abundance of MdPIN1 encoding an auxin efflux carrier but a higher transcript abundance of MdGH3-2 encoding a putative auxin amido conjugate synthase, resulting in a lower free auxin concentration; feeding the transgenic leaves with exogenous auxin partially restores leaf width. MdbHLH3 transcriptionally suppresses and activates MdPIN1 and MdGH3-2, respectively, by specifically binding to their promoters. This alters auxin homeostasis and transport, consequently leading to changes in leaf shape. These findings suggest that the bHLH TF MdbHLH3 directly modulates auxin signaling in controlling leaf shape in response to local spatial gradients in apple.

Euryale Small Auxin Up RNA62 promotes cell elongation and seed size by altering the distribution of indole-3-acetic acid under the light

“…In maize, ZmPIN1a has been reported to regulate auxin spatiotemporal asymmetric distribution in multiple plant developmental processes (Li et al, 2018). Suppressing apple auxin efflux carrier MdPIN1 has an impact on leaf shape (Hu et al, 2020). A recent study in Nymphaea colorata showed that PIN1, PIN3, and PIN7 are involved in the regulatory network of flower development (Zhang et al, 2020).…”

Genome-wide identification and stress response analysis of cyclophilin gene family in apple (Malus × domestica)

“…The MdActin (GenBank accession number CN938024) was used as the internal control. Quantitative analysis of gene expression was performed based on the 2 -∆∆CT method [ 69 ]. Specific primers of the MdCYPs gene were designed and listed in Supplementary Table 4 .…”

Roles of Auxin in the Growth, Development, and Stress Tolerance of Horticultural Plants

“…An apple basic/helix–loop–helix transcription factor MdbHLH3 is expressed at a higher level at a higher altitude. It controls leaf shape by specifically activating auxin amido conjugate synthase gene MdGH3-2 and suppressing pin-formed auxin efflux transporter gene MdPIN1 [ 54 ]. The NAC transcription factor VviNAC33 of grapevine ( Vitis vinifera L.) is a negative regulator of the auxin pathway.…”