Dear Editor,rnGravitropism in plants is key for orienting organs such as the Darwin’s description of the opposite growth direction of roots and shoots in his book The Power of Movement in Plants more than 100 years ago (Darwin,1880).The gravitropic response of an oriented plant is divided into three sequential phases:gravity sensing,signal transmission,and the growth response.As the initial phase of gravitropism,gravity sensing (the conversion of the mechanical stimulus into a biochemical signal) has been intensively studied,but much is still unknown.