Breeding and Field Performance of Novel Soft and Waxy Transgenic Rice Lines without Selectable Markers

Abstract

Amylose content is one of the important factors affecting rice cooking and eating quality, and controlled by the Waxy (Wx) gene which encoding a granule-bound starch synthase. High amylose levels are usually associated with poor cooking and eating quality. In our prevrious studies, in order to generate transgenic rice varieties with improved quality and without of the selectable marker, the antisense Wx gene was co-transformed together with a selectable marker gene, the hygromycin-resistant gene (HPT), to a high-yielding japonica rice cultivar, Wuxiangjing 9, mediated with Agrobacterium tumeficien. And some select-able marker-free (SMF) transgenic lines had been subsequently selected. In present study, several homozygous transgenic lines with soft or waxy grain property were selected from the offspring of these SMF transformants containing the antisense Wx gene. The results from Northern blot analysis indicated that the levels of both the Wx mature mRNA and unspliced transcripts were reduced differently in the endosperm of different transgenic lines. The Wx protein level in mature seeds of the transgenic lines was also reduced differently. The amylose content of two transgenic lines was reduced to that of soft rice (about 10%) and one line was reduced to that of waxy rice (lower than 2%). The gel consistency of these transgenic lines was softer than that of the wild type. The variance of gelatination temperature between the transgenic lines and the wild type did not reach to significant level. The most of the main agronomic traits of these transgenic lines were similar to that of the wild type. Therefore, three SMF trans-genic homozygous lines with improved quality were successfully bred.