Biology subjects

Gangappa, S. N.

Publications and source records attributed to Gangappa, S. N..

4 recordsLinked to original sources

bioRxiv2026

Non-canonical role of a PHOSPHATE1 HOMOLOG 2 in suppressing seedling photomorphogenesis via the TOC1-PIF4 module

Photomorphogenesis, the light-driven development of seedlings, is governed by a complex network of transcription factors and circadian regulators. While the TIMING OF CAB EXPRESSION 1 (TOC1) is known to link circadian rhythms with light-responsive growth, the mechanisms fine-tuning its activity remain poorly understood. Here, we identify PHOSPHATE 1 HOMOLOG 2 (PHO1;H2) as a novel negative regulator of seedling photomorphogenesis in Arabidopsis. Loss-of-function pho1;h2 mutants exhibit hypersensitivity to light, characterized by markedly shorter hypocotyls and increased photopigment accumulation, whereas overexpression lines display reduced photomorphogenic response. We demonstrate that the N-terminal SPX domain of PHO1;H2 is both necessary and sufficient to repress seedling photomorphogenic growth. Mechanistically, in vitro and in vivo interaction assays reveal that the SPX domain physically binds and sequesters TOC1, inhibiting its regulatory function. This PHO1;H2-mediated sequestration of TOC1 alleviates the repression of PHYTOCHROME INTERACTING FACTOR 4 (PIF4), thereby promoting the expression of downstream genes involved in cell elongation and hormone signaling. Collectively, our findings reveal a competitive binding mechanism by which PHO1;H2 modulates the TOC1-PIF4 signaling axis, providing a crucial checkpoint for seedling growth in dynamic light environments.

plant biology↗

bioRxiv2024

Threshold-dependent negative autoregulation of PIF4 gene expression optimizes growth and fitness in Arabidopsis

PHYTOCHROME INTERACTING FACTOR 4 (PIF4) is a vital transcription factor that controls plant growth by integrating environmental signals like light and temperature. Though upstream regulators of PIF4 are known, transcriptional regulation of PIF4 is poorly understood. Here, we demonstrate that the PIF4 undergoes negative autoregulation. We show that PIF4 promoter activity is more in the pif4 mutant but significantly reduced in PIF4 overexpression transgenic lines. Moreover, CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), which enhances PIF4 protein stability, promotes PIF4 autoinhibition. However, Phytochrome B (phyB), a photoreceptor that decreases PIF4 stability, inhibits autoinhibition. We further develop a network-based mathematical model incorporating the PIF4 autoinhibition and other key interactions. Our modeling and data analysis reveals that PIF4 autoregulation depends on a threshold of cellular PIF4 concentration. Our model also successfully predicts the hypocotyl growth and PIF4 promoter activity in various light and temperature conditions. Moreover, we show that the transgenic lines with enhanced PIF4 function negatively influence biomass and yield, irrespective of photoperiod and temperature. Together, the negative feedback of PIF4 dampens its own function and restraints unregulated growth. Our study thus elucidates the mechanisms of how the phyB-COP1/DET1-PIF4 module controls PIF4 transcription in tune with the endogenous PIF4 level.

plant biology↗

bioRxiv2024

Unequal genetic redundancies among MYC bHLH transcription factors underlie seedling photomorphogenesis in Arabidopsis

Light is one of the most critical ecological cues controlling plant growth and development. Plants have evolved complex mechanisms to cope with fluctuating light signals. In Arabidopsis, bHLH transcription factors MYC2, MYC3, and MYC4 have been shown to play a vital role in protecting plants against herbivory and necrotrophic pathogens. While the role of MYC2 in light-mediated seedling development has been studied in some detail, the role of MYC3 and MYC4 still needs to be discovered. Here, we show that MYC4 negatively regulates seedling photomorphogenesis, while the MYC3 function seems redundant. However, the genetic analysis reveals that MYC3/MYC4 together act as positive regulators of seedling photomorphogenic growth as the myc3myc4 double mutants showed exaggerated hypocotyl growth compared to myc4 single mutants and Col-0. Intriguingly, the loss of MYC2 function in the myc3myc4 double mutant background (myc2myc3myc4) resulted in further enhancement in the hypocotyl growth than myc3myc4 double mutants in WL, BL and FRL, suggesting that MYC2/3/4 together play an essential and positive role in meditating optimal seedling photomorphogenesis. Besides, MYC3/MYC4 genetically and physically interact with HY5 to partially inhibit its function in controlling hypocotyl and photo-pigment accumulation. Moreover, our results suggest that COP1 physically interacts and degrades MYC3 and MYC4 through the 26S proteasomal pathway and controls their response to dark and light for fine-tuning HY5 function and seedling photomorphogenesis.

plant biology↗

bioRxiv2024

The ELF3-BBX24/BBX25-PIF4 module controls thermosensory growth in Arabidopsis

Temperature serves as a crucial environmental cue governing the growth and adaptation of plants in their natural habitat. PHYTOCHROME INTERACTING FACTOR 4 (PIF4) is a central regulator that promotes thermomorphogenesis in Arabidopsis. Understanding its precise regulation is critical for optimal thermomorphogenic growth. Here, we identified two BBX proteins, BBX24 and BBX25, as novel components of the PIF4-mediated thermosensory pathway and act to promote warm temperature-mediated growth. The bbx24 and bbx25 single and double mutants showed moderate to strong temperature-insensitive hypocotyl and cotyledon growth. Warm temperature induces BBX24 and BBX25 mRNA expression and protein accumulation. Genetic and biochemical analysis revealed that BBX24/BBX25 promotes PIF4-mediated thermosensory growth by counteracting a key component of the evening complex, ELF3. While ELF3 inhibits BBX24/BBX25 gene expression at low ambient temperatures in the evening, warm temperature-mediated inhibition of ELF3 activity results in enhanced BBX24/BBX25 activity. Moreover, BBX24/25 inhibit ELF3 function through direct physical interaction and likely relieves repression on PIF4, enhancing its activity and thermomorphogenesis. Together, this study unravels ELF3-BBX24/BBX25-PIF4 as a key regulatory module that controls growth and development under varying temperature cues.

plant biology↗