Frontiers in Plant Science (Apr 2021)
The MADS-Box Transcription Factor EjAGL65 Controls Loquat Flesh Lignification via Direct Transcriptional Inhibition of EjMYB8
Abstract
Loquat fruit accumulates lignin in its flesh when undergoing chilling injury during postharvest storage, making it a suitable model for the study of flesh lignification. Transcriptional regulation of lignin biosynthesis is principally controlled by the NAC-MYB transcriptional cascade in model plants. Previous research has demonstrated that EjMYB8 activates lignin biosynthesis through direct interaction with the promoter of Ej4CL1. However, the classic NAC-MYB gene regulation network has not been established. Here, the MADS-box gene EjAGL65 was discovered by screening a cDNA library using the EjMYB8 promoter as bait in yeast. A phylogenetic analysis and structural comparisons revealed that EjAGL65 belongs to the Mδ subgroup of the MADS-box family, whose members have not been reported as being involved in the regulation of lignin deposition. EjAGL65 transcription was downregulated at 0°C compared to 5°C, indicating a negative correlation with the change of lignin content. A dual-luciferase assay indicated that EjAGL65 is capable of inhibiting the promoter activity of EjMYB8 in vivo. These results showed that the Mδ MADS-box gene EjAGL65 transcriptionally regulates EjMYB8 during postharvest chilling induced flesh lignification, which differs from the classical regulation model of lignin biosynthesis that has been illustrated for developmental lignin accumulation.
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