Researchers from the Department of Biochemistry at the Indian Institute of Sciences (IISc) have discovered a long-sought mechanism used by primitive land plants such as bryophytes (including mosses and liverworts) to regulate plant growth – a mechanism that has also been conserved in more recently evolved flowering plants.
The study, published in the journal Nature Chemical Biology, focuses on the non-classical regulation of the DELLA protein, a master growth regulator that can inhibit cell division in embryonic plants (land plants).
”DELLA acts like a speed bump, but if this speed bump is constantly present, the plant cannot move,” explains Debabrata Laha, associate professor of biochemistry and co-author of the study. Therefore, the degradation of DELLA proteins is critical for promoting plant growth. In flowering plants, DELLA is degraded when the phytohormone gibberellin (GA) binds to its receptor GID1, forming the GA-GID1-DELLA complex. Subsequently, the DELLA repressor protein binds to ubiquitin chains and is degraded by the 26S proteasome.
Interestingly, bryophytes were among the first plants to colonize land, approximately 500 million years ago. Although they produce the phytohormone gibberellin (GA), they lack the GID1 receptor. This raises the question: how were the growth and development of these early land plants regulated?
The researchers used the CRISPR-Cas9 system to knock out the corresponding VIH gene, thereby confirming the role of VIH. Plants lacking a functional VIH enzyme exhibit severe growth and developmental defects and morphological abnormalities, such as dense thallus, impaired radial growth, and lack of calyx. These defects were corrected by modifying the plant genome to produce only one end (the N-terminus) of the VIH enzyme. Using advanced chromatography techniques, the research team discovered that the N-terminus contains a kinase domain that catalyzes the production of InsP₈.
The researchers discovered that DELLA is one of the cellular targets of VIH kinase. Furthermore, they observed that the phenotype of MpVIH-deficient plants was similar to that of Miscanthus multiforme plants with increased DELLA expression.
”At this stage, we are eager to determine whether DELLA stability or activity is enhanced in MpVIH-deficient plants,” said Priyanshi Rana, a doctoral student in Lahey’s research group and the paper’s first author. Consistent with their hypothesis, the researchers found that DELLA inhibition significantly restored the growth and development defects in MpVIH mutant plants. These findings suggest that VIH kinase negatively regulates DELLA, thereby promoting plant growth and development.
The researchers combined genetic, biochemical, and biophysical methods to elucidate the mechanism by which inositol pyrophosphate regulates DELLA protein expression in this bryophyte. Specifically, InsP₈, produced by MpVIH, binds to the MpDELLA protein, promoting its polyubiquitination, which in turn leads to the degradation of this repressor protein by the proteasome.
Research on the DELLA protein dates back to the Green Revolution, when scientists unknowingly exploited its potential to create high-yielding semi-dwarf varieties. Although its mechanism of action was unknown at the time, modern technologies have enabled scientists to use gene editing to manipulate the function of this protein, thereby effectively increasing crop yields.
”With population growth and shrinking arable land, increasing crop yields has become critical,” Raha said. Given that InsP₈-regulated DELLA degradation can be widespread in embryonic plants, this discovery could pave the way for the development of next-generation high-yielding crops.
Post time: Oct-31-2025