The CUP-SHAPED COTYLEDON2 and 3 genes have a post-meristematic effect on Arabidopsis thaliana phyllotaxis

Abstract
Background and Aims: The arrangement of flowers in inflorescence shoots of Arabidopsis thaliana represents a regular spiral Fibonacci phyllotaxis. However, in the cuc2 cuc3 double mutant, flower pedicels are fused to the inflorescence stem, and phyllotaxis is aberrant in the mature shoot regions. This study examined the causes of this altered development, and in particular whether the mutant phenotype is a consequence of defects at the shoot apex, or whether post-meristematic events are involved. Methods: The distribution of flower pedicels and vascular traces was examined in cross-sections of mature shoots; sequential replicas were used to investigate the phyllotaxis and geometry of shoot apices, and growth of the young stem surface. The expression pattern of CUC3 was analysed by examining its promoter activity. Key Results: Phyllotaxis irregularity in the cuc2 cuc3 double mutant arises during the post-meristematic phase of shoot development. In particular, growth and cell divisions in nodes of the elongating stem are not restricted in the mutant, resulting in pedicel-stem fusion. On the other hand, phyllotaxis in the mutant shoot apex is nearly as regular as that of the wild type. Vascular phyllotaxis, generated almost simultaneously with the phyllotaxis at the apex, is also much more regular than pedicel phyllotaxis. The most apparent phenotype of the mutant apices is a higher number of contact parastichies. This phenotype is associated with increased meristem size, decreased angular width of primordia and a shorter plastochron. In addition, the appearance of a sharp and deep crease, a characteristic shape of the adaxial primordium boundary, is slightly delayed and reduced in the mutant shoot apices. Conclusions: The cuc2 cuc3 double mutant displays irregular phyllotaxis in the mature shoot but not in the shoot apex, thus showing a post-meristematic effect of the mutations on phyllotaxis. The main cause of this effect is the formation of pedicel-stem fusions, leading to an alteration of the axial positioning of flowers. Phyllotaxis based on the position of vascular flower traces suggests an additional mechanism of post-meristematic phyllotaxis alteration. Higher density of flower primordia may be involved in the post-meristematic effect on phyllotaxis, whereas delayed crease formation may be involved in the fusion phenotype. Promoter activity of CUC3 is consistent with its post-meristematic role in phyllotaxis. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

Citation
Burian A, Raczy ska-Szajgin M, Borowska-Wykr t D, Piatek A, Aida M, et al. (2015) The CUP-SHAPED COTYLEDON2 and 3 genes have a post-meristematic effect on Arabidopsis thaliana phyllotaxis. Annals of Botany 115: 807–820. Available: http://dx.doi.org/10.1093/aob/mcv013.

Publisher
Oxford University Press (OUP)

Journal
Annals of Botany

DOI
10.1093/aob/mcv013

PubMed ID
25681504

PubMed Central ID
PMC4373294

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