Biology subjects

Rengasamy, B.

Publications and source records attributed to Rengasamy, B..

3 recordsLinked to original sources

bioRxiv2025

A non-canonical MPK3-ACTPK1-RbcS signalling module fine-tunes photosynthesis in rice

Chloroplast protein import is essential for photosynthesis, yet whether and how cytosolic signaling pathways dynamically regulate this process remains largely unknown. Here we uncover a signaling module that links mitogen activated protein kinase (MAPK) activity to fine tune the import of small subunit of Rubisco (RbcS) into the chloroplast. We show that MPK3 negatively regulates the cytosolic Raf-like kinase ACTPK1, which directly phosphorylates the transit peptide of RbcS precursor at Thr12. MPK3 directly phosphorylates ACTPK1, attenuating its kinase activity and thereby limiting RbcS transit peptide phosphorylation. Genetic and physiological analyses demonstrate that loss of MPK3 elevates ACTPK1 activity, increases RbcS phosphorylation and enhances Rubisco accumulation and CO2 assimilation. On the other hand, ACTPK1 deficiency compromises these processes and photosynthetic performance. Phospho-mutant analyses further reveal that reversible phosphorylation of the RbcS transit peptide is required for efficient chloroplast import. Together, our findings establish chloroplast protein import as a signaling-regulated process and identify transit peptide phosphorylation a key check point integrating cytosolic MAPK signaling with photosynthetic capacity.

plant biology↗

bioRxiv2025

A positive feedback loop of MPK3-PIN1A trafficking-auxin flux trio governs dual gravitropic and wounding response in rice

The auxin flow in plants plays a pivotal role in gravitropic organ movement and tissue regeneration following injury. However, the regulatory aspects of these phenomena are not entirely understood. In this study, we found that hyperactivity of MAP Kinase 3 (MPK3) led to downregulation of PINs and reduction in tissue auxin content, impairing gravitropic response of rice and accelerating tissue senescence following mechanical wounding. The MPK3 was found to phosphorylate PIN1A majorly at its Ser351 residue, mutation of which into its phospho-mimic variant enhanced latters endosomal trafficking and consequently improved auxin flux. Further, overexpression of the phospho-null variant of PIN1A lowered gravitropic response of rice, thus causing wider tiller angle similar to the pin1a knockout lines. Additionally, upon wounding, their tissue senescence was faster in comparison to the overexpression lines of wild-type and phospho-mimic variants of PIN1A, which also displayed improved resistance to wounding by Bipolaris oryzae. The PIN1A trafficking-mediated auxin flux also regulated MPK3 activity via a positive feedback loop. Together, these results uncover a novel feedback loop encompassing "MPK3-PIN1A trafficking-auxin flux" trio that regulates dual gravitropic and wounding response in rice.

plant biology↗

bioRxiv2024

Phosphorylation of KRP3, a KIP-related protein by MPK3 modulates rice tiller and seed number by fine-tuning cell division

During the cell cycle process, multiple inhibitors function as checkpoint regulators ensuring an impeccable duplication of genetic material. Kip-Related Proteins (KRPs) are a group of plant-specific cell cycle inhibitors and are known to regulate plant architecture and yield by differentially regulating cell division. KRPs, though functionally conserved, are dynamic in their amino acid composition. Interestingly, some KRPs are specific to dicots, and some are for monocots. In this study, we have identified that the presence of KRP3 and KRP6 is specific to the Poaceae family of monocots. An in-depth study of KRP3 showed a strict regulation of its expression in actively dividing cells during the G1-S phase progression of cell division. Our study identified KRP3 as a phosphorylation target of MPK3. The phosphorylation enhances KRP3 protein stability, which leads to strong inhibition of cell proliferation. By generating knock-out lines of krp3, mpk3 and double knock-out krp3mpk3, our study demonstrated that the MPK3-KRP3 module regulates rice root and shoot development as well as tiller and seed numbers. It was observed that KRP3 regulate the rate of cell division in a dose-dependent manner. The study, in a nutshell, establishes the role of KRP3 as an important regulator of rice vigor and yield.

plant biology↗