Regulation of loquat fruit low temperature response and lignification involves interaction of heat shock factors and genes associated with lignin biosynthesis

• Published in: Plant, cell and environment Vol. 39; no. 8; pp. 1780 - 1789
• Main Authors: Zeng, Jiao‐ke, Li, Xian, Zhang, Jing, Ge, Hang, Yin, Xue‐ren, Chen, Kun‐song
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.08.2016
• Subjects: Biosynthesis; Chilling injury; Cold Temperature; cold tolerance; cold treatment; Eriobotrya - genetics; Eriobotrya - metabolism; Eriobotrya japonica; flesh lignification; fluorescence; Fruit - metabolism; Fruits; gene expression; Gene Expression Regulation, Plant; heat shock factor; heat shock protein; heat shock proteins; Heat Shock Transcription Factors - genetics; Heat Shock Transcription Factors - metabolism; Heat treatment; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; HSF‐AP2 complex; hybrids; lignification; lignin; Lignin - biosynthesis; loquats; Low temperature; protein-protein interactions; regulator genes; temperature; transcription (genetics); transcription factors; trees; woody plants; Yeasts; HSF-AP2 complex; heat shock protein; heat treatment; heat shock factor; flesh lignification; Chilling injury
• ISSN: 0140-7791; 1365-3040; 1365-3040
• DOI: 10.1111/pce.12741

Transcriptional regulatory mechanisms underlying lignin metabolism have been widely studied in model plants and woody trees, as well as fruit, such as loquat (Eriobotrya japonica). Unlike the well‐known NAC, MYB and AP2/ERF transcription factors, the roles of heat shock factors (HSFs) in lignin regulation have been rarely reported. Two treatments (heat treatment, HT; low temperature conditioning, LTC) were applied to alleviate low temperature‐induced lignification in loquat fruit. Gene expression analysis indicated that EjHSF1 transcript abundance, in parallel with heat shock protein genes (EjHsp), was induced by HT, while expression of EjHSF3 was repressed by LTC. Using dual‐luciferase assays, EjHSF1 and EjHSF3 trans‐activated the promoters of EjHsp genes and lignin biosynthesis‐related genes, respectively. Thus, two distinct regulatory mechanisms of EjHSF transcription factors in chilling injury‐induced fruit lignification are proposed: EjHSF1 transcriptionally regulated EjHsp genes are involved in chilling tolerance, while EjHSF3 transcriptionally regulated lignin biosynthesis. Furthermore, the relations between EjHSF3 and previously characterized fruit lignification regulators, including EjAP2‐1, EjMYB1 and EjMYB2, were also investigated. Yeast‐two hybrid (Y2H) and biomolecular fluorescence complementation (BiFC) assays demonstrated protein‐protein interaction between EjHSF3 and EjAP2‐1. Thus, the involvement of EjHSF3 in fruit lignification is via both lignin biosynthetic genes and the regulator, EjAP2‐1. Fruit may be subject to chilling injury during postharvest low temperature storage, and heat treatments have been shown to alleviate chilling injury symptoms in many fruit species. The present research showed that heat shock factors (HSF) are involved in loquat fruit chilling injury and induced lignification via two distinct pathways. EjHSF1 transcriptionally regulated EjHsp genes, while EjHSF3 interacted with EjAP2‐1 and regulated lignin biosynthetic genes.