摘要In plants, cortical microtubules anchor to the plasma membrane in arrays and play important roles in cell shape. However, the molecular mechanism of mi-crotubule binding proteins, which connect the plasma membrane and cortical microtubules in cell morphology remains largely unknown. Here, we re-port that a plasma membrane and microtubule dual-localized IQ67 domain protein, IQD21, is critical for cotyledon pavement cell (PC) morphogenesis in Arabidopsis. iqd21 mutation caused increased in-dentation width, decreased lobe length, and similar lobe number of PCs, whereas IQD21 over-expression had a different effect on cotyledon PC shape. Weak overexpression led to increased lobe number, decreased indentation width, and similar lobe length, while moderate or great overexpression resulted in decreased lobe number, indentation width, and lobe length of PCs. Live-cell observations revealed that IQD21 accumulation at indentation re-gions correlates with lobe initiation and outgrowth during PC development. Cell biological and genetic approaches revealed that IQD21 promotes trans-facial microtubules anchoring to the plasma mem-brane via its polybasic sites and bundling at the in-dentation regions in both periclinal and anticlinal walls. IQD21 controls cortical microtubule organ-ization mainly through promoting Katanin 1-mediated microtubule severing during PC interdigitation. These findings provide the genetic evidence that transfacial microtubule arrays play a determinant role in lobe formation, and the insight into the molecular mechanism of IQD21 in transfacial microtubule or-ganization at indentations and puzzle-shaped PC development.