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Researchers at the National Institute of Plant Genome Research (NIPGR), New Delhi have identified a ‘master gene’ in rice that breeders can target for better yields. Rice yield is especially measured by the number of grains per plant and grain weight. Currently Breeders are attempting to reinforce these parameters to extend rice productivity. The grain size(polygenic trait) of rice is set by multiple genes or genomic loci known as Quantitative Trait Loci or QTL. However, quantity traits are polygenic in nature. Till now, scientists have identified more than 40 major QTLs or genes in the rice genome associated with grain size and weight. However, how these genes coordinate to regulate the grain size and shape is still unknown.

The researchers had found in earlier studies that expression of a particular gene, OsMed15a, was higher at different stages of seed development. The observation led them to explore its role further. They scanned 509 different rice genotypes and found that the nucleotide sequences of the OsMed15a gene varied depending on size of grain. OsMed15a was also found to play major role in regulating the expression of three other genes — GW2GW5 and DR11I- which determine grain size and weight.

“When we suppressed the expression of OsMed15a in transgenic plants using RNAi technology, the seeds became smaller and wider,” said Jitender K Thakur, lead researcher, while speaking to India Science Wire. For further work, the group is collaborating with Ranchi-based Indian Institute of Agriculture Biotechnology so that grain size could be increased substantially through standard breeding methods.

This study is important as it establishes OsMed15a as a connecting link between some of the different genes important for grain size / weight trait in rice. In the next phase, using high throughput ‘omics’ tools, we would be delineating complete network of genes and proteins being connected through OsMed51a,” Thakur said.

He also noted that the size and shape of the rice grain is not only important for boosting yield but also contributes to the market value of rice. “Indians prefer long and slender rice grains. There are some small grained rice which are full of pleasant aroma. We are trying to introgress long grain allele of OsMed15a in these varieties so that the seeds become longer. We hope that in this way we would be able to produce location-specific long grain aromatic rice”, he added.

The research team included Swarup K Parida, Nidhi Dwivedi, Sourobh Maji, Mohd Waseem, Pallabi Thakur and Vinay Kumar. The study results will be published in journal BBA — Gene Regulatory Mechanisms. This work was supported by grants from Science and Engineering Research Board (SERB) and Department of Biotechnology (DBT). (India Science Wire)

References:

Dwivedi, N. et al. The Mediator subunit OsMED15a is a transcriptional co-regulator of seed size/weight–modulating genes in rice. BBA  Gene Regul. Mech. (2019) doi: 10.1016/j.bbagrm.2019.194432