Minisymposium 8: Cell division

Abs # 21002: A Novel role for Two NAC-like Genes in Regulating Meristematic Activity in Arabidopsis

Presenter:	Yang, Chang-Hsien , chyang@dragon.nchu.edu.tw
Authors	Shih, Ching-Fang  (A)   Yang, Chang-Hsien  (A)
Affiliations:	(A): Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227 ROC

NAC-like genes that contained a conserved 150 amino acid NAC domain at their N-terminus of proteins have been thought to be involved in regulation of many processes of plant development. AtNACL1 and AtNACL2, with conserved NAC domain, were identified in Arabidopsis. Both AtNACL1 and AtNACL2 mRNA were detected in the inflorescence meristem, floral buds, and leaves. AtNACL1 mRNA is expressed much higher than AtNACL2 in root. Transgenic Arabidopsis plants ectopically expressed AtNACL1 or AtNACL2 were phenotypically indistinguishable from wild-type plants. By contrast, shoot and leaf formation was severe altered in T-DNA insertional or antisense mutants of AtNACL1 and AtNACL2 by producing serrated leaves with abnormal shape and generating a bushy phenotype with numerous inflorescences. In addition, two to three flowers along with cauline leaves or secondary inflorescence were produced in an internode normally only occupied by a single flower in the inflorescence of a wild type plant. Interestingly, the alteration of flower organ formation was also observed in mutants of AtNACL1 and AtNACL2 during late flower development. In addition to the production of novel shoot phenotype, novel phenotype of roots were also observed in these AtNACL1 or AtNACL2 mutant plants. In wild-type Arabidopsis, the root apical meristem divided rapidly and generated a single main root with several lateral roots. By contrast, AtNACL1 and AtNACL2 mutant roots produced numerous main roots from the embryonic root after germination. During late of the root development, numerous branches of roots were continually produced almost in the anyplace of the AtNACL1 or AtNACL2 mutant roots and resulted in a great mass of fibrous like roots that were significantly different from that of a wild-type root. These results clearly indicated that AtNACL1 and AtNACL2 are involved in the controlling of meristematic activity for shoot, flower and root formation. Further analysis indicated that the mutant phenotypes were correlated with the alteration of the expression for genes involved in meristematic development such as SERRATE and cytokinin regulating pathway such as KNAT1 in mutants of AtNACL1 and AtNACL2. To investigate AtNACL1, 2 action, yeast two-hybrid assays using AtNACL1 or AtNACL2 as a bait was carried out. Further identification and analysis of the interacting proteins should provide new insight of the function for NAC-like genes in regulating meristematic activity in plants.