<i>Arabidopsis </i><scp>DEFECTIVE KERNEL</scp>1 regulates cell wall composition and axial growth in the inflorescence stem

Abstract

Abstract Axial growth in plant stems requires a fine balance between elongation and stem mechanical reinforcement to ensure mechanical stability. Strength is provided by the plant cell wall, the deposition of which must be coordinated with cell expansion and elongation to ensure that integrity is maintained during growth. Coordination of these processes is critical and yet poorly understood. The plant‐specific calpain, DEFECTIVE KERNEL 1 ( DEK 1), plays a key role in growth coordination in leaves, yet its role in regulating stem growth has not been addressed. Using plants overexpressing the active CALPAIN domain of DEK 1 ( CALPAIN OE ) and a DEK 1 knockdown line ( ami RNA ‐ DEK 1 ), we undertook morphological, biochemical, biophysical, and microscopic analyses of mature inflorescence stems. We identify a novel role for DEK 1 in the maintenance of cell wall integrity and coordination of growth during inflorescence stem development. CALPAIN OE plants are significantly reduced in stature and have short, thickened stems, while ami RNA ‐ DEK 1 lines have weakened stems that are unable to stand upright. Microscopic analyses of the stems identify changes in cell size, shape and number, and differences in both primary and secondary cell wall thickness and composition. Taken together, our results suggest that DEK 1 influences primary wall growth by indirectly regulating cellulose and pectin deposition. In addition, we observe changes in secondary cell walls that may compensate for altered primary cell wall composition. We propose that DEK 1 activity is required for the coordination of stem strengthening with elongation during axial growth.