Abstract
Phytochrome-interacting factor 4 (PIF4) participates in light signaling by interacting with photoreceptors, phytochromes, and cryptochromes. Although well characterized in Arabidopsis, PIF4′s role in crop plants is unknown. Here we performed the first integrated genomics, transcriptomics, and molecular characterization of PIF4 in soybean (Glycine max) plants. Fifteen identified Glycine max PIFs (GmPIFs) grouped into PIF3, PIF4, and PIF8 subfamilies based on their phylogenetic relationships. The GmPIF4 subfamily formed two distinct clades (GmPIF4 I and GmPIF4 II) with different amino acid sequences in the conserved bHLH region. Quantitative transcriptional analysis of soybean plants exposed to different photoperiods and temperatures indicated that all PIF4 I clade GmPIF4s conserved PIF4-like expression. Three out of four GmPIF4 transcripts of the GmPIF4 I clade increased at 35 °C compared to 25 °C under short day conditions. RNA sequencing of soybeans undergoing floral transition showed differential regulation of GmPIF4b, and ectopic GmPIF4b expression in wild type Arabidopsis resulted in an early flowering phenotype. Complementation of GmPIF4b in Arabidopsis pif4-101 mutants partially rescued the mutant phenotype. PIF4 protein levels peaked before dawn, and a GmPIF4b protein variant was observed in soybean plants treated at high temperatures.
Highlights
Environmental factors such as light and temperature have a profound effect on plant physiology and development; their presence and the duration of exposure[1]
In the model plant Arabidopsis thaliana, phytochrome interacting factors (PIFs) belong to the basic helix-loop-helix (bHLH) superfamily of proteins, with the PIF subfamily consisting of PIF1, PIF3, Phytochrome-interacting factor 4 (PIF4), PIF5, PIF6, PIF7, and PIF84
The bHLH domain contains a stretch of 50–60 amino acids that comprises two segments: a stretch of around 40 amino acids forming two amphipathic α-helices separated by a variable length loop and a 10–15 basic amino acid domain with DNA-binding capacity[5]
Summary
Environmental factors such as light and temperature have a profound effect on plant physiology and development; their presence and the duration of exposure[1]. It has recently been suggested that PIF4 acts as an integrating hub for light and temperature-related signals and the evening circadian clock-expressed factor TOC1 to regulate thermoresponsive plant growth[9]. PIF4 interacts with the blue light receptor CYPTOCHROME 1 (CRY1) to regulate high temperature-mediated hypocotyl elongation by increasing IAA concentrations through stimulation of YUC8 (YUCCA8) and TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) gene expression[12]. The presence of multiple forms/ copies of a gene is often linked to the acquisition of new functions (neo-functionalization) or division of labor to divide the function (sub-functionalization) in a species These gene diversification events lay the foundation for phenotypic variability and adaptability in plants[15]. Soybean cultivars are divided into different maturity groups depending on day length requirements, and some of the quantitative trait loci that affect soybean flowering have recently been reported[17,18,19]
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