The miR156-SPL9-ARR2 module promotes zeatin signal and increases the fruit shape index in persimmon

This is the authors' abstract. We don't add key points for this paper.

Persimmon ( Diospyros kaki Thunb.) exhibits a wide diversity in fruit shape index (FSI, the ratio of longitudinal diameter to transverse diameter). However, the molecular regulatory mechanism underlying FSI formation remains unclear. In this study, comparative cellular observation, mRNA, and microRNA (miRNA) transcriptome analyses were conducted between the long and flat shape groups across three developmental stages, S2 (May 28), S3 (June 14), and S5 (July 3), respectively. These stages were found to be critical for the formation of FSI. Fruit shape variation was driven by both cell number and cell volume, with the cell number dominating longitudinal elongation and the cell volume dominating transverse expansion. According to weighted gene co-expression network analysis (WGCNA), two modules were positively correlated ( p = 0.05) with the FSI at stages S3 and S5. Transcription factor (TF) genes ABI8 and MYB98 were identified from the hub-genes in this module, and ARR2 that potentially encodes a cytokinins (CTKs) response protein was also screened from these hub-genes. Additionally, 5 long-shape promoting miRNA-mRNA regulators (with low-level miRNA and high-level mRNA targets in long-shape fruits), at the same time, 17 long-shape inhibiting regulators were identified. The miR156- SPL is one of the long-shape inhibiting regulators, because high-level miR156 members and low-levels of their SPL9 target were found in long-shape fruits, which supported a hypothesis that the suppression of SPL to the ARR gene that encodes CTKs response protein might be alleviated, thus the FSI might be increased with more CTKs signals. This hypothesis was confirmed to some extent by the fact that exogenous application of zeatin increased the flat persimmon FSI. This study partly elucidates the molecular basis of persimmon fruit shape and can provide certain guidance for molecular breeding of persimmon fruit shape.