Transgenic tobacco over-expressing a homeobox gene shows a developmental interaction between leaf morphogenesis and phyllotaxy

The tobacco gene, NTH1, encodes a polypeptide of 326 amino acids and is a m ember of the class1 KN1-type family of homeobox genes. Expression of NTH1 h as mainly been observed in vegetative and reproductive shoot spices, not ob served in roots or expanded leaves. Over-expression of NTH1 in transgenic p lants caused abnormal leaf morphology, consisting of wrinkling and curvatur e, Interestingly, the direction of leaf curvature tended to be conserved am ong almost all of the leaves in any given transformant. In transgenic plant s exhibiting clockwise or anticlockwise phyllotaxy, leaves curved to the ri ght or left, respectively, when looking from the shoot apex toward the base . Micro-surgical experiments demonstrated that the presence of the shoot ap ex is necessary for the development of leaf curvature, indicating that the order of formation of leaves on the stem (the generative spiral) affects le af development. We found a correlation between the severity of leaf curvatu re and the value of the plastochron ratio, a parameter of phyllotaxy. Trans formants with more severe phenotypes had larger plastochron ratios. From th ese findings, we discuss the possibility that an increase in the plastochro n ratio, caused by over-expression of NTH1 in the shoot apex, may be involv ed in leaf curvature.