Role of Gibberellins in panicle architecture of Rice

Akash Singh, Banaras Hindu University

In the developing world, rice (Oryza sativa) is the main nutritional crop and the staple food of more than half the population of the world. This is an excellent source of complex carbohydrates, rich in nutrients, vitamins and minerals. Rice supplies 21% of the total human energy per capita and 15% of the protein per capita. The research focused for decades on improving rice production to meet the demands of a rapidly growing population. The number of spikes per panicle is a key determinant of grain yield in rice. New research published in the journal Plant Biotechnology explains the role of gibberellins in the panicle architecture of rice, how gibberellins affect the DELLA–KNOX signalling which further mediates the panicle architecture.

Role of quantitative trait loci (QTL) in regulating rice panicle architecture:

The QTL is a region of DNA associated with specific phenotypes, varying in degree to polygenesis effects, namely two or more genes and their environment. The QTL is a quantitatively characteristic region of DNA. Dozens of quantitative trait locus (QTL) that contribute to the morphology of panicles and grain outcome have also been identified. For example Dense and Erect Panicle1 (DEP1) and Ideal Plant Architecture 1 (IPA1) in japonica rice and Narrow Leaf 1 (NAL1) in indica varieties. Some of the genes in these QTLs have been identified recently utilizing sequence, bioinformatics, and analysis of the natural allelic diversity.

DELLA mediated Gibberellic Acid (GA) signalling:

Phyto-hormones of gibberellic acid (GA) are known to affect various plant development processes such as the elongation of the stem, flowering, pollen maturation, and germination of seed. In the penultimate step of GA biosynthesis, four genes encoding 20-oxidases (OsGA20ox1-4) have been considered to play a part. The two different Ga oxidases are encoded in, for example, semi dwarf1 (SD1) and panicle grains number (GNP1).

DELLA proteins are highly preserved GRAS family transcription regulators that usually act as negative GA signalling regulators. DELLA proteins are highly conserved. DELLA proteins lack diagnostic components but interact with a variety of regulatory proteins — transcriptions, transcriptions, chromatographic rework complexes and co-chaperones — to regulate DELLA proteins downstream processes.

By evaluating expression patterns in genes like D2 (Ebisu dwarf), MADS34, ASP1, OSCSLD4, IPA1, DTH7, TAW1, DEP1, and FUWA they found that changes to the GA synthesis can cause changes in transcription for some genes for panicle development.

Identification of qPA1:

qPA1 (QTL for panicle architecture on chromosome 1) has been identified by researchers that regulate the architecture of rice panicles. They demonstrated that qPA1 is similar to SD1 through map-oriented cloning and supplementation tests, which controls the rice panicle and the spikelet number through DELLA–Class 1 KNOX pathway positively.

SD1 is found globally in the development of plants, particularly in vegetative organs, according to our PCR-qRT findings, which show expressions in leaves, leaf sheaths, roots and panicles. The Nipponbare genome SD1 sequence has been introduced into CSSL-9 for examining whether SD1 is responsible for the qPA1 phenotype. All the 20 T1 transformers were significantly longer than the CSSL-8 lines in panicle, higher plant height, higher primary and secondary branch numbers and total panicle grain number confirmed SD1 as the causal gene for qPA1. CRISPR/Cas9 has been applied for the elimination of SD1 from Nipponbare and Kasalath lines to confirm the similarity of SD1 to qPA1.

Research Prospect:

Researchers were able to use map-based cloning and complementary experiments for qPA1 QTL to identify SD1 gene similitudes known to affect panicle and plant height development. The SD1 gene has been used successfully. They have proposed an AG regulatory model for the development of panicles in SD1 mutants and wild plants based on their results. Such measures would encourage the expression of downstream effector genes, as ASP1 promotes panicle growth if DELLA (SLR1) expression is degraded and KNOX class 1 gene expression increases in wild panicle type development. Conversely, non-functional SD1 in SD1 mutants leads to SLR1 accumulation and functional sequestration of OSH1 to reduce the activation of genes involved in panicle development.

Their study provides a basis for the production of high yield rice. The combination of these two QTLs (GNP1 and SD1) also provides new breeding objectives for the refinement of panicle architecture.

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Source: Su, S., Hong, J., Chen, X., Zhang, C., Chen, M., Luo, Z., Chang, S., Bai, S., Liang, W., Liu, Q., & Zhang, D. (2021), Gibberellins orchestrate panicle architecture mediated by DELLA–KNOX signalling in rice. Plant Biotechnology Journal. https://doi.org/10.1111/pbi.13661

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Author’s info: Akash Singh is a first-year masters student of Biochemistry at Banaras Hindu University. He plans to pursue a PhD in the future. He aims to research and teach the young minds of the country.