Investigating the Role of MYC3 and MYC4 in Light and Temperature-Mediated Regulation of Growth and Development in Arabidopsis

Garhwal, Vikas (2024) Investigating the Role of MYC3 and MYC4 in Light and Temperature-Mediated Regulation of Growth and Development in Arabidopsis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesi sof Vikas Garhwal (17RS018)) 17RS018.pdf - Submitted Version Restricted to Repository staff only Download (8MB)

Abstract

Light is one of the most vital ecological cues controlling plant growth and development. Plants have evolved complex and coordinated regulatory mechanisms to cope with dynamic light cues. Moreover, plants also respond to changes in response to warm ambient temperature, known as thermomorphogenesis. Thermomorphogenesis is characterized by elongation in hypocotyl, changes in cotyledon growth at the seedlings stage, and increased petiole length, rosette diameter, hyponastic growth, and early flowering at the adult stage, thereby improving plant survival at higher temperatures. In Arabidopsis, bHLH transcription factors, MYC2, MYC3, and MYC4, have been shown to play a critical 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. We show that MYC4 negatively regulates seedling photomorphogenesis, while the MYC3 function seems redundant. However, the genetic analysis indicates that MYC3/MYC4 together act as positive regulators of seedling photomorphogenic growth as the myc3myc4 double mutants display 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 in dark and light for fine-tuning HY5 function and seedling photomorphogenesis. Besides, a detailed analysis of various myc mutants revealed that MYC2/3/4 also plays a crucial role in the temperature-mediated regulation of growth and development. Genetic studies confirm that MYC3 and MYC4 probably strongly regulate PIF4 function to inhibit hypocotyl growth but promote its function to enhance cotyledon growth under warm ambient temperatures. Surprisingly, the elongated hypocotyl length of myc234 mutant promotes early flowering in response to warm ambient temperature, which may be indirectly/directly linked to PIF4. Together, this study unravels the role of MYC transcription factors in light and temperature-mediated growth control.

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