Maize LOST SUBSIDIARY CELL encoding a large subunit of ribonucleotide reductase is required for subsidiary cell development and plant growth

The maize LSCgene, encoding a large subunit of ribonucleotide reductase, modulates dNTP synthesis, subsidiary cell development and plant growth. The four-celled stomatal complex consists of a pair of guard cells (GCs) and two subsidiary cells (SCs) in grasses, which supports a fast adjustment of stomatal aperture. The formation and development of SCs are thus important for stomatal functionality. Here, we report a maize lost subsidiary cells (lsc) mutant, with many stomata lacking one or two SCs. The loss of SCs is supposed to have resulted from impeded subsidiary mother cell (SMC) polarization and asymmetrical division. Besides the defect in SCs, the lsc mutant also displays a dwarf morphology and pale and striped newly-grown leaves. LSC encodes a large subunit of ribonucleotide reductase (RNR), an enzyme involved in deoxyribonucleotides (dNTPs) synthesis. Consistently, the concentration of dNTPs and expression of genes involved in DNA replication, cell cycle progression, and SC development were significantly reduced in the lsc mutant compared with the wild-type B73 inbred line. Conversely, overexpression of maize LSC increased dNTP synthesis and promoted plant growth in both maize and Arabidopsis. Our data indicate that LSC regulates dNTP production and is required for SMC polarization, SC differentiation, and growth of maize.

Automated summary

The maize LSC gene, encoding a large subunit of ribonucleotide reductase, plays a crucial role in dNTP synthesis, subsidiary cell development, and plant growth. The loss of subsidiary cells in the maize lsc mutant is attributed to impaired subsidiary mother cell polarization and division. In addition to the defect in subsidiary cells, the lsc mutant exhibits a dwarf morphology and pale and striped newly-grown leaves. Our findings indicate that LSC is essential for dNTP production, subsidiary mother cell polarization, subsidiary cell differentiation, and overall maize growth.