Scientists Found the Way for Rice Root Enineering

The phytohormone cytokinin (CK) is one of five phytohormones, which positively regulates the activity and function of the shoot apical meristem (SAM) and participates in plant development, morphogenesis, and many other physiological processes. The rice (Oryza sativa L.) Gn1a/OsCKX2 (Grain number 1a/Cytokinin oxidase 2) gene, which encodes a cytokinin oxidase/dehydrogenase (CKX) family gene, has been identified as a major quantitative trait locus contributing to grain number improvement in rice breeding practice. However, it is still unknown how cytokinin regulates rice root development.

 

A team led by Prof. CHU Chengcai of the State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, recently revealed the molecular mechanism of cytokinin regulating rice crown root initiation and development.

 

Roots are very important to plants for various functions, including water and nutrient uptake, anchoring, mechanical support, and storage. Rice has a dense fibrous root system that includes embryonic roots, crown roots (also known as adventitious roots or shoot-borne roots), and lateral roots. Previous work revealed auxin, a phytohormone, plays an important role in crown root initiation and development. However, the mechanism of cytokinin in rice crown root initiation and development is not well understood.

 

CHU’s team identified a root enhancer1 (ren1-D) mutant by a large-scale screening of rice T-DNA activation-tagging population. Molecular and genetic analyses revealed that these phenotypes were caused by the activation of another CKX family gene OsCKX4. OsCKX4 is preferentially expressed in the shoot base where crown root primordia are produced and induced by exogenous auxin and cytokinin in the roots. Further analyses demonstrated that OsCKX4 integrated cytokinin and auxin signaling to control rice crown root formation.

 

Most interesting, the plants with overexpression of OsCKX4 under the control of a root-specific promoter RCc3 displayed enhanced root development. This provides a potential strategy for improvement of crop nutrient uptake and abiotic stress tolerance capacity by ‘root engineering’.

 

Gao S, Fang J, Xu F, Wang W, Sun X, Chu J, Cai B, Feng Y, Chu C (2014) A cytokinin oxidase/dehydrogenase gene OsCKX4 integrates cytokinin and auxin signaling to control rice crown root formation. Plant Physiol. DOI:10.？1104/？pp.？114.？238584