Cloning of cDNAs specifically expressed in wheat spikelets at the heading stage, as identified by the simple differential display method

Abstract

Wheat cDNAs expressed in the spikelets at the heading stage were isolated according to the PCR-mediated simple differential display method. The wheat spikelets at the heading stage contain a pair of glumes, a lemma, a palea, a pair of lodicules, three stamens and a pistil. Anthers harbor bi-, and tri-nucleate pollen cells. Out of 76 RAPD primers examined, 13 primers gave 29 spikelet-specific bands. After cloning of these bands, 34 independent cDNAs were recovered by the DNA sequencing of these clones. A homology search of these cDNAs showed the existence of genes homologous to meristem identity genes such as LEAFY and APETALA1 in Arabidopsis as well as other flower organ specific genes encoding UFO, pollen-, anther-, inflorescence-, and immature flower-specific proteins. Additionally, novel genes in the plants were obtained. Northern blot analysis of these clones revealed that rare as well as abundant mRNAs were also clonable, and 14 cDNAs were specifically or highly expressed in the flower organs rather than in the other tissues including young spikes. Fourteen cDNAs were classified into six groups, based on the hybridization patterns. Furthermore, the six groups were divided into two major groups: (1) cDNAs specifically expressed in certain tissues of the wheat flower (lodicule, stamen, pistil and lemma/palea-pistil), and (2) cDNAs continuously transcribed in the flower organs. These genes might play roles in gamete formation and/or maintain the activity of flower organs at the heading stage.