KATANIN promotes cell elongation and division to generate proper cell numbers in maize organs.

Microtubule severing is essential for proper eukaryotic cell elongation and division. Here we show that the microtubule severing protein, KATANIN p60, is encoded by two genes in Zea mays L. (maize) called Discordia3a (Dcd3a) and Dcd3b. A semi-dominant mutant with short stature, poor fertility, and a clumped tassel was identified in Dcd3b called Clumped tassel1 (Clt1). Genetic enhancers that further reduced stature and fertility were identified in inbred lines and mapped to the Dcd3a locus, identifying several dcd3a alleles. Loss-of-function p60 allele combinations reduce microtubule severing, fertility, and cell elongation. Cell elongation defects, in turn, contribute to G1 delay. KATANIN p60 is important for preprophase band (PPB) formation and positioning, and nuclear positioning in symmetric cell divisions. Misoriented PPBs lead to offset nuclei and rare misoriented symmetric divisions in mutants. A combination of these defects contributes to generating small mutant plants with fewer cells.