Semi-dominant mutations in the gene encoding histidine kinase influences rice morphology.

Abstract

Cytokinin plays a major role in the regulation of plant development. It is perceived by receptors with histidine kinase activity to regulate the expression of various transcription factors. In the previous study, we reported a semi-dominant mutant, named adaxial-abaxial bipolar leaf1 (abl1)-d, which exhibited a characteristic feature in the fourth leaf of rice and that the ABL gene encodes a cytokinin receptor with histidine kinase activity. Our further analysis suggested that the abl1-d mutation is associated with a putative active form of histidine kinase and altered cytokinin signaling. However, it remains unclear whether abl1-d mutation indeed triggers aberrant cytokinin signal in rice plants, and how the abl1-d mutation affects developmental processes throughout the lifecycle of rice. In the present study, we found that homozygous abl1-1d calli have the capacity to regenerate shoots in the absence of cytokinin, suggesting that the abl1-1d homozygous mutation is associated with constitutive cytokinin signaling in rice. We next examined morphological characteristics of both homozygous and heterozygous abl1-1d plants from the post-germination vegetative phase through to reproduction. The results showed that homozygous abl1-1d plants had a reduced number of panicles and were completely sterile, and that leaf size and the midrib structure were altered. Furthermore, the adaxial-abaxial bipolar leaf, a phenotype that is characteristic of the abl1-1d mutant, has been observed to resemble two normal leaves fused together at their abaxial sides. The leaf with this particular phenotype exhibited enhanced photosynthetic efficiency under certain environmental conditions. Thus, the abl1-1d mutants, which express a putative active form of histidine receptor kinase, affect various developmental traits throughout the rice lifecycle probably due to altered cytokinin signaling.