Robust circadian rhythms of gene expression in Brassica rapa tissue culture.

Xiaodong Xu,Qiguang Xie,C Robertson Mcclung

doi:10.1104/pp.110.155465

Abstract

Circadian clocks provide temporal coordination by synchronizing internal biological processes with daily environmental cycles. To date, study of the plant circadian clock has emphasized Arabidopsis (Arabidopsis thaliana) as a model, but it is important to determine the extent to which this model applies in other species. Accordingly, we have investigated circadian clock function in Brassica rapa. In Arabidopsis, analysis of gene expression in transgenic plants in which luciferase activity is expressed from clock-regulated promoters has proven a useful tool, although technical challenges associated with the regeneration of transgenic plants has hindered the implementation of this powerful tool in B. rapa. The circadian clock is cell autonomous, and rhythmicity has been shown to persist in tissue culture from a number of species. We have established a transgenic B. rapa tissue culture system to allow the facile measurement and manipulation of clock function. We demonstrate circadian rhythms in the expression of several promoter:LUC reporters in explant-induced tissue culture of B. rapa. These rhythms are temperature compensated and are reset by light and temperature pulses. We observe a strong positive correlation in period length between the tissue culture rhythm in gene expression and the seedling rhythm in cotyledon movement, indicating that the circadian clock in B. rapa tissue culture provides a good model for the clock in planta.

Highlights

Circadian clocks provide temporal coordination by synchronizing internal biological processes with daily environmental cycles
Most that is known about the mechanism of the plant circadian clock is based on Arabidopsis, and it is important to determine the extent to which the circadian clock model developed in Arabidopsis can be extended to other plants, especially to crop species
King and colleagues adapted an automated imaging system to measure cotyledon movement in B. oleracea and used this assay to demonstrate transgressive variation in period length and to map quantitative which is consistent with the period lengthening seen in loss-of-function ztl mutants (Somers et al, 2000)

Summary

Introduction

Circadian clocks provide temporal coordination by synchronizing internal biological processes with daily environmental cycles. Since the separation of their common ancestor from Arabidopsis some 16 to 21 million years ago (Koch et al, 2001), Brassica genomes have triplicated (O’Neill and Bancroft, 2000; Rana et al, 2004; Parkin et al, 2005; Town et al, 2006; Yang et al, 2006) and, in some cases, further undergone polyploidization through hybridization (U, 1935), offering opportunity for novel functional diversification, including in circadian timekeeping In this context, it is worth recalling that altered expression of clock genes has been implicated in heterosis, the increased growth vigor often seen in hybrids and allopolyploids (Ni et al, 2009)

Methods

Results

Conclusion