Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

West, Nick [1], Golenberg, Edward [1].

Feminization pathway mediated by GAI repressor protein in Spinacia oleracea.

Hormones are known to be involved in sexual development in numerous plant species displaying a variety of reproductive types (monoecious, dioecious, gynodioecious etc.). Sexual development of spinach, a type II dioecious species, is influenced by the phytohormone gibberellic acid (GA) and is known to be masculinizing. The mechanism defining hormone influence over sexual development remains an active area of research in many species, here we describe an important link between the GA response pathway and floral organ identity pathway in spinach. This study focused on altering the endogenous levels of GA or its effector protein GIBBERELIC ACID INSENSITIVE (GAI) in spinach. We utilized a RNAi knockdown (KD) mediated approach to reduce the expression of GAI. qPCR was used to characterize expression of GAI in male and female individuals as well as to evaluate the effectiveness of GAI knockdown treatments. GAI KD resulted in a range of floral phenotypes that are likely correlated to the range of knockdown efficiencies inherent in the RNAi system. Observed floral phenotypes include wild-type female, wild-type male, and hermaphrodite flowers. These phenotypes were observed on the same plant and often within the same inflorescence. Interestingly, homeotic mutants were also observed as a result of GAI KD. With some regularity carpels would be seen developing in place of one or more stamen. Expression of GAI was observed to be significantly higher in wild-type females compared to wild-type males. GAI KD plants exhibited lower GAI expression than females and sometimes even lower than males. The variance in GAI expression among GAI KD samples was higher than that found in either control males or females and is consistent with the mosaic phenotypic knockdown pattern and variable penetrance seen previously in our VIGS based system. The observations that GAI KD masculinizes the plant and the differential expression of GAI between males and females suggest, that the repressor protein GAI has a critical function in sexual determination in spinach. The presence of GAI may prevent the transcription of the male specific B-class genes thus flowers will develop only female organs. Elevated levels of the phytohormone gibberellic acid causes the degradation of GAI thus releasing the repression of the B-class genes and male flowers develop. Previous work has shown spinach B-class genes cause the repression of carpel development resulting in flowers with only male organs. These observations suggest that GAI is crucial to feminization in spinach sex determination.

1 - Wayne State University, Department of Biological Sciences, 5047 Gullen Mall , Detroit, MI, 48201, USA

Keywords:
dioecy
spinach
sex determination
gibberellic acid
feminization
GAI
gibberellic acid insensitive
floral development.

Presentation Type: Oral Paper:Papers for Topics
Session: 42
Location: Hall B/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 11:30 AM
Number: 42006
Abstract ID:111
Candidate for Awards:Katherine Esau Award