NAC072 Interacts with HB12, HAT9, and MYBR1 in a Temporal Regulatory Network Controlling Peach Fruit Development

Fruit development is a complex process that involves the interplay of different biological processes carefully coordinated to control fruit quality traits. The peach fruit development consists in four recognized growth stages (S1–S4). The second stage (S2) is characterized by the endocarp hardening process and is followed by the second exponential growth phase (S3), where an increase in fruit size is produced by a rapid cell expansion. A nectarine genotype incapable of ripening and described as a slow ripening phenotype was identified and selected as a good model for studying peach fruit development. Slow ripening fruit remained firm, green, and exhibited no rise in CO₂ or ethylene production rates blocking fruit development at S3 stage. The transcription factor NAC072 has been proposed as a key regulatory element involved in both the slow ripening and the harvest date phenotypes. However, the regulatory mechanisms by which NAC072 produces these phenotypic changes are still unknown. Using a transcriptomic approach between normal and slow ripening individuals with a transcription factor–gene target interaction database, a NAC072 regulatory network was constructed, identifying putative direct and indirect NAC072 fruit development-related elements. Three transcription factors were identified along with NAC072 in early stages of fruit development, two homeobox-leucine zippers (HB12 and HAT9), and one MYB transcription factor (MYBR1). In addition, we determined that the NAC072 transcriptional regulatory network promotes phenylpropanoids biosynthesis and cell wall remodeling to develop fruit growth, seed development, and softening, probably through hormonal signaling pathways involving abscisic acid and gibberellic acid.