Dynamic patterns of expression for genes regulating cytokinin metabolism and signaling during rice inflorescence development

Abstract

Inflorescence development in cereals, including such important crops as rice, maize, and wheat, directly affects grain number and size and is a key determinant of yield. Cytokinin regulates meristem size and activity and, as a result, has profound effects on inflorescence development and architecture. To clarify the role of cytokinin action in inflorescence development, we used the NanoString nCounter system to analyze gene expression in the early stages of rice panicle development, focusing on 67 genes involved in cytokinin biosynthesis, degradation, and signaling. Results point toward key members of these gene families involved in panicle development and indicate that the expression of many genes involved in cytokinin action differs between the panicle and vegetative tissues. Dynamic patterns of gene expression suggest that subnetworks mediate cytokinin action during different stages of panicle development. The variation of expression during panicle development is greater among genes encoding proteins involved in cytokinin metabolism and negative regulators of the pathway than for the genes in the primary response pathway. These results provide insight into the expression patterns of genes involved in cytokinin action during inflorescence development in a crop of agricultural importance, with relevance to similar processes in other monocots. The identification of subnetworks of genes expressed at different stages of early panicle development suggests that manipulation of their expression could have substantial effects on inflorescence architecture.

Type-B response regulators of rice play key roles in growth, development, and cytokinin signaling

“…S5C). The specificity of the rr24 mutant phenotype is consistent with analyses indicating that the expression of RR24 increases when floral meristems are produced and that RR24 is the most highly expressed type-B RR in mature anthers (Li et al, 2007;Patel et al, 2012;Yamburenko et al, 2017).…”

“…Panicle architecture is determined by meristems that give rise to the branches and spikelets, and mutants affecting cytokinin biosynthesis and degradation have revealed a crucial role for cytokinin in regulating this phenotype (Ashikari et al, 2005;Gu et al, 2015;Kurakawa et al, 2007;Yeh et al, 2015). RR21 and RR23 are expressed early during panicle meristem development, consistent with the defects in primary and secondary branch formation arising from their loss (Yamburenko et al, 2017). A role for type-B RRs in cell proliferation was indicated by the decrease in leaf size and cell number in the rr21/22/23 mutant.…”

“…A defect in anther development was uncovered in rr24 mutants; RR24 is a rice type-B RR that exhibits maximal expression during later stages of panicle meristem development when floral organs are produced and also maintains a high level of expression in the anther itself (Li et al, 2007;Patel et al, 2012;Yamburenko et al, 2017). An RR24 mutation was also recently uncovered independently in a forward genetic screen to identify the basis for sterility in the rice lepto1 mutant (Zhao et al, 2018), the pollen mother cells in this mutant arresting early during prophase I of meiosis, thereby accounting for the lack of pollen production.…”

“…For plants grown in soil, a 1:1 ratio of Pro-mix BX Mycorrhizae and Profile Porous Ceramic Greens Grade was used, supplemented with water-soluble nitrogen/phosphorous/potassium (NPK) fertilizer (20-20-20; 2.9 g/l) and iron (Fe) fertilizer (Sprint 330; 0.48 g/l). Plants were grown in a greenhouse at 30°C during the day and 25°C at night, using a 10-h light/14-h dark cycle as described elsewhere (Yamburenko et al, 2017). For growth of seedlings on media, dehusked seed was sterilized with 50% (v/v) bleach solution for 30 min, washed with sterile water, germinated at 37°C for 16 h and then generally transferred to one-half strength Kimura's medium (Yoshida et al, 1976) solidified with 0.4% (w/v) Phytoagar (PlantMedia) and grown at 30°C/28°C with a 12-h light/12-h dark cycle (light=400 µE).…”

Histidine kinase MHZ1/OsHK1 interacts with ethylene receptors to regulate root growth in rice

“…Two-component systems also participate in cytokinin signaling in Arabidopsis and similar mechanism may exist in rice 38,47,[60][61][62][63] . Considering that rice may have only two functional HPts (OsAHP1 and OsAHP2) for signaling 47,48 , it is hence possible that these two genes play roles in both ethylene signaling and cytokinin signaling in specific manners depending on distinct treatments, times, cell types, tissues and/or organs.…”