CDC48 is a member of the AAA ATPase superfamily. Yeast CDC48 and its mammalian homolog p97 are implicated in diverse cellular processes, including mitosis, membrane fusion, and ubiquitin-dependent protein degradation. However, the cellular functions of plant CDC48 proteins are largely unknown. In the present study, we performed virus-induced gene silencing (VIGS) screening and found that silencing of a gene encoding a tobacco CDC48 homolog, NgCDC48, resulted in severe abnormalities in leaf and shoot development in tobacco. Furthermore, transgenic tobacco plants (35S:anti-NgCDC48), in which the NgCDC48 gene was suppressed using the antisense RNA method, exhibited severely aberrant development of both vegetative and reproductive organs, resulting in arrested shoot and leaf growth and sterile flowers. Approximately 57-83% of 35S:anti-NgCDC48 plants failed to develop mature organs and died at early stage of development. Scanning electron microscopy showed that both adaxial and abaxial epidermal pavement cells in antisense transgenic leaves were significantly smaller and more numerous than those in wild type leaves. These results indicate that NgCDC48 is critically involved in cell growth and development of tobacco plants. An in vivo targeting experiment revealed that NgCDC48 resides in the endoplasmic reticulum (ER) in tobacco protoplasts. We consider the tantalizing possibility that CDC48-mediated degradation of an as-yet unidentified protein(s) in the ER might be a critical step for cell growth and expansion in tobacco leaves.
To take into account the flexibility resulting from sectional deformations of a thin-walled box beam, higher-order beam theories considering warping and distortional degrees of freedom (DOF) in addition to the Timoshenko kinematic degrees have been developed. The objective of this study is to derive the exact matching condition consistent with a 5-DOF higher-order beam theory at a joint of thin-walled box beams under out-of-plane bending and torsion. Here we use bending deflection, bending/shear rotation, torsional rotation, warping, and distortion as the kinematic variables. Because the theory involves warping and distortion that do not produce any force/moment resultant, the joint matching condition cannot be obtained just by using the typical three equilibrium conditions. This difficulty poses considerable challenges because all elements of the 5 x 5 transformation matrix relating the field variables of one beam to those in another beam should be determined. The main contributions of the investigation are to propose additional necessary conditions to determine the matrix and to derive it exactly. The validity of the derived joint matching transformation matrix is demonstrated by showing good agreement between the shell finite element results and those obtained by the present box beam analysis in various angle box beams.
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