Lab Made Story #1

"Gravity" is one of the things we learn from high school physics classes and the tendency of any object towards gravity is known as "Gravitropism". Plants are no exception to that universal rule. The gravitropism of plant root was revealed by Charles Darwin and his son almost 140 years ago and published in the book The Power of Movement in Plants. So far our understanding about root gravitropism is connected to plant hormone auxin, master molecule responsible (or believe) for almost every developmental process. Auxin flows from both shoot to root and root to shoot directions. Asymmetric auxin distribution during root to shoot transport helps plant root to bend towards gravity. This has been well established through auxin transport mutant (eir1/pin2) phenotype. This protein actually works as an auxin transporter from root to shoot direction. Its mutant doesn't follow gravity at all. We may call it, blind to gravity. 


Recently Liangfa Li and Rujin Chen have published an article and reported one mutant which shows negative gravitropic response rather than being blind to gravity. They have confirmed this negative gravitropic phenotype in both legume species Medicago truncatula and model plant Arabidopsis thaliana. They named it NGR or Negative Gravitropic Response of Root. In this mutant, root simply grow on the opposite of the gravity, even if you change the direction of the gravity over the time. Interestingly, Arabidopsis carries 3 similar orthologs of that gene and they function redundantly. Single and double mutants don't show negative gravitropic phenotype, but triple mutants confirm it. In triple mutant background, one of the three genes may complement the gravitropic phenotype. 

Authors: Liangfa Li and Rujin Chen
Journal: Nature Plants 

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