Research Summary: Our study shows that rice heat shock transcription factor OsHSFC1b enhances seed vigor, weight, and size, but isoaspartyl modification impairs its function. PIMT, a protein repairing enzyme, repairs the modification, restoring HSFC1b activity and improving agronomic traits.
Author interview
Mr. Rakesh Kumar Achary is pursuing a Ph.D. at BRIC-NIPGR, New Delhi. He completed his Master’s degree in botany from Utkal University, Odisha. His doctoral work focuses on studying various aspects governing seed development, vigor, and longevity.
Twitter: https://x.com/acharyrakesh96
Instagram: https://www.instagram.com/the_acharyrakesh/
Lab: Dr. Manoj Majee, Scientist, BRIC-National Institute of Plant Genome Research
Twitter: https://x.com/manojmajeenipgr
Seed and stress biology lab: https://x.com/mm_lab_nipgr
Lab Website: https://nipgr.ac.in/nipgrv2/dr_mmajee.html
What was the core problem you aimed to solve with this research?
Seed proteins are highly vulnerable to post-translational modifications, such as carbonylation, sulfoxidation, and isoaspartyl modification. These chemical alterations are often triggered by the oxidative and desiccated environment of seeds, leading to structural perturbations and functional impairments in proteins. Such damage can negatively influence critical agronomic traits, including seed vigor, viability, and proper seed development. Among these modifications, isoaspartyl (isoAsp) formation in rice seed proteins remains poorly characterized, representing a significant gap in our understanding of seed protein stability and function.
To mitigate such detrimental changes, seeds have evolved specialized protein-repair enzymes. One of the most prominent is PROTEIN L-ISOASPARTYL METHYLTRANSFERASE (PIMT), a highly conserved and seed-abundant enzyme that specifically recognizes and repairs isoAsp residues, thereby restoring protein functionality. Our previous work has demonstrated that PIMT plays a pivotal role in maintaining seed vigor and viability (longevity) in rice. Building on this foundation, the present study seeks to identify PIMT-interacting proteins in rice, with the goal of elucidating its broader regulatory network in targeting and repairing isoaspartyl-modified proteins, and ultimately understanding its contribution to seed quality and agronomic performance.
How did you go about solving this problem?
To investigate the role of PIMT in rice seeds, we employed immunoprecipitation followed by mass spectrometry using an anti-PIMT antibody on aged rice seed extracts. Through this approach, we identified the rice heat shock transcription factor OsHSFC1b as a potential interacting partner of PIMT. This unexpected finding raised intriguing questions: What is the significance of the PIMT–HSF interaction? Does OsHSFC1b accumulate isoaspartyl residues, and if so, what are the biological consequences?
Using a combination of in vitro and in vivo assays, we discovered that OsHSFC1b indeed accumulates isoaspartyl modifications, which impair its transactivation function. Remarkably, PIMT was able to repair this modification and fully restore HSFC1b’s activity. Expression analysis revealed that OsHSFC1b is abundant in seeds, with levels increasing progressively during seed development.
To further explore its biological role, we generated OsHSFC1b overexpression (OE) lines and CRISPR–Cas9 genome-edited (GE) lines in both wild-type (WT) and PIMT-deficient backgrounds. Detailed phenotypic characterization showed that OsHSFC1b enhances seed vigor, viability, seed weight, and seed size. However, these beneficial effects were significantly reduced in the absence of PIMT, particularly under seed aging or stress conditions. Together, our findings reveal a critical functional partnership between PIMT and OsHSFC1b in maintaining seed performance and resilience.
Key findings to the non-scientific community?
“It’s not just about growing more grains; it’s about growing grains that last.”
In today’s world, the demand for high grain yields is ever-increasing. But it’s not just about producing more grains; it’s about producing grains that can sprout quickly, grow uniformly, and stay viable during storage. This quality, known as seed vigor and longevity, determines how well seeds perform from planting to harvest.
Our research shows that a key protein, HSFC1b, working in partnership with another important seed regulator, PIMT, a protein repairing enzyme, plays a vital role in maintaining seed vigor and longevity. Not only does this partnership help seeds germinate better and last longer in storage, but it also boosts seed size and weight traits, which are highly valuable to farmers.
We also discovered that under stress, a subtle chemical change, i.e., isoaspartyl modification in the seed protein, HSFC1b, can reduce its effectiveness, but PIMT acts like a repair tool to restore its full function. By understanding and enhancing this natural repair process, we can improve seed quality in ways that have real-world benefits, helping farmers produce healthier crops, improve grain quality, and ultimately strengthen food security.
Research in my laboratory centers around studying molecular intricacies, mechanisms, and events that govern desiccation tolerance to orthodox seeds, while intolerance to recalcitrant seeds, and how plants manage to achieve optimal seed size, weight, and vigor across diverse environmental conditions. – Dr. Manoj Majee
What are the potential implications of your findings for the field and society?
Seed longevity is essential for preserving the genetic diversity of both cultivated and endangered plant species. In agriculture, maintaining seed vigor and longevity during storage is especially crucial, as in subtropical climates, many crop seeds deteriorate rapidly, losing their ability to germinate and significantly impacting agricultural productivity and the economy.
Our findings have both scientific and societal significance. Scientifically, we’ve uncovered a novel functional partnership between a seed repair enzyme (PIMT) and a heat shock transcription factor (OsHSFC1b) in rice, showing how repairing subtle protein damage can directly influence seed vigor, longevity, size, and weight. This opens new avenues for crop breeding and seed biotechnology aimed at enhancing seed performance, especially under stress or during long-term storage.
From a societal perspective, improving seed vigor and storage life has direct implications for food security and sustainable agriculture. Farmers could store seeds longer without losing germination potential, plant seeds that establish faster and more uniformly, and harvest crops with higher yield quality. Ultimately, our work contributes to producing more reliable, high-quality seeds, which benefits both the farming community and consumers.
What was the exciting moment during your research?
One of the most exciting aspects of our research was starting with a simple but fascinating question: Why can some seeds remain viable for centuries, like the lotus seed (Nelumbo nucifera, ~1,300 years) or the date palm (Phoenix dactylifera, over 2,000 years), while others lose their ability to germinate within days? This curiosity drove us to explore the traits that govern seed longevity.
During our experiments, we discovered that the transcription factor HSFC1b plays multiple roles in seeds, not only supporting vigor and longevity but also influencing seed size and weight. Finding such a single factor with diverse agronomic functions was truly novel. Even more intriguing, we found that isoaspartyl modification of HSFC1b can impair its biological activity, but the protein repair enzyme PIMT can reverse this damage, especially under aging and storage conditions. Seeing how this molecular “repair crew” restores seed function was a particularly thrilling moment in our research journey.
Paper reference: Achary, R.K., Kamble, N.U., Gautam, S., Hazra, A., Varshney, V., Mahawar, S., Laha, S. and Majee, M. (2025). The rice heat shock transcription factor OsHSFC1b increases seed weight, size, and vigor, but its function is disrupted by isoaspartyl modification. Plant Journal, 123: e70365. https://doi.org/10.1111/tpj.70365
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