Analysis of Rice Mutants Defective in Shoot Development and Associated with Biosynthesis of Very-Long-Chain Fatty Acids

Very-long-chain fatty acids (VLCFAs) are components of cuticle wax and protect plants from environmental stresses. Rice mutants of ONION1 (ONI1) and ONI2, both of which encode fatty acid elongase involved in the biosynthesis of VLCFAs, had a reduced amount of VLCFAs and showed defects in epidermis development. Thus, VLCFAs seemed to be important molecules for shoot development.

To further understand a function of VLCFA biosynthesis genes and a physiological role of VLCFAs in shoot development in rice, we screened mutants that resembled the shoot morphology of oni1 and oni2, and identified two mutants. SEM analysis showed that these mutants lacked protrusions of cuticle on the leaf surface. Expression of ROC1, a marker gene of an outermost cell layer, was reduced. These results suggest that differentiation of epidermis is perturbed in these mutants. Epidermis is known to be a preferential pathway for polar auxin transport. Consistent with abnormal development of epidermis, expression of PIN genes, which encode an efflux carrier of polar auxin transport, and IAA genes, whose expression is induced by auxin, was perturbed, suggesting that auxin distribution is altered in the shoot.

Our analyses revealed that the two mutants showed similar phenotypes to oni1 and oni2, and thus, the two mutants will be also associated with VLCFAs. Further analyses of these mutants will clarify the function of VLCFAs in rice shoot development.

This study is supported by Global Science Campus program from JST.