Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Molecular, Cellular, and Developmental Biology

First Advisor

David J. Hannapel


The objective of this study was to gain insight into how classes of regulatory genes affect the growth and development of potato, particularly, the molecular processes of tuberization. This was accomplished by generating transgenic potato plants that overexpress the homeobox gene, POTH1 , and by using an antisense approach to suppress levels of the MADS box gene, POTM1.;POTH1 was shown to be involved in vegetative pattern formation via mediation of hormone levels. Overexpression of POTH1 resulted in dwarf plants with a 'mouse-ear' leaf phenotype. Leaves were heart-shaped with a decreased midvein and palmate venation. POTH1 overexpression lines exhibited an increase in both the rate of tuberization and the total number of tubers formed in vitro, overcoming the negative effects of a long-day photoperiod on tuberization. Enhanced tuberization can be partially attributed to the decrease in the levels of active gibberellin (GA) caused by POTH1 suppression of the GA biosynthesis gene, GA 20-oxidase1. Similar to other knox genes, POTH1 appears to be a negative regulator of GA biosynthesis.;Suppression of the MADS box gene, POTM1, in potato activated axillary meristem growth. The phenotype of POTM1 suppression lines was characterized by reduced apical dominance, increased lateral growth, and the formation of shoot clusters on the stem. There was also an increase in starch accumulation and cell division, a reduction in tuber formation, and an inhibition of root formation on cuttings. Initiation of axillary meristem formation was not altered, as both the location and number of axillary meristems was normal. Rather, phenotypic alterations are mediated by the activation of axillary meristem growth. The POTM1 suppression phenotype has many similarities to mutants in which the Agrobacterium ipt gene was introduced to overproduce cytokinin. These cytokinin overproduction phenotypes include loss of apical dominance, decreased leaf size and internode length, and poor root growth. POTM1 appears to be involved in maintaining the proper balance of growth between vegetative meristems and lateral organs.



Digital Repository @ Iowa State University,

Copyright Owner

Faye Michelle Rosin



Proquest ID


File Format


File Size

125 pages