CiSPL31, an SPL transcription factor, promotes fruit enlargement and increases fruit size by upregulating SEPALLATA2 and LONGIFOLIA 3 in pecan (Carya illinoinensis).

Abstract

The SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family has been implicated in various plant growth and developmental processes; however, its role in flowering and fruit development remains poorly characterized in pecan (Carya illinoinensis). In this study, we identified 32 SPL genes in the pecan genome and divided them into six groups which displayed structurally conserved within groups but show structural divergence between groups. they Furthermore, transcriptome and RT-qPCR analysis indicated that CiSPL31 was highly expressed in flower buds and early developing fruits. Subcellular localization and transcriptional activation activity assay demonstrated that CiSPL31 is a nuclear-localized transcription factor with transcriptional activity. Overexpression of CiSPL31 in Arabidopsis promoted primary root elongation, flowering, and increased seed size and 1000-seed weight. And the expression of several seed size positive regulators, such as SEP2, FUL, LNG3, SHB1 and so on, were upregulated in CiSPL31 overexpression lines. Yeast one-hybrid and luciferase assays confirmed that CiSPL31 positively regulates CiSEP2 and CiLNG3 transcription by directly binds to the GTAC motif in the CiSEP2 and CiLNG3 promoter regions. Overall, our results provide a comprehensive understanding of the potential functions of the SPL family genes and a novel regulatory network of fruit size in pecan.