SRD1 is involved in the auxin-mediated initial thickening growth of storage root by enhancing proliferation of metaxylem and cambium cells in sweetpotato (Ipomoea batatas)

Abstract

A sweetpotato (Ipomoea batatas cv. ‘Jinhongmi’) MADS-box protein cDNA (SRD1) has been isolated from an early stage storage root cDNA library. The role of the SRD1 gene in the formation of the storage root in sweetpotato was investigated by an expression pattern analysis and characterization of SRD1-overexpressing (ox) transgenic sweetpotato plants. Transcripts of SRD1 were detected only in root tissues, with the fibrous root having low levels of the transcript and the young storage root showing relatively higher transcript levels. SRD1 mRNA was mainly found in the actively dividing cells, including the vascular and cambium cells of the young storage root. The transcript level of SRD1 in the fibrous roots increased in response to 1000 μM indole-3-acetic acid (IAA) applied exogenously. During the early stage of storage root development, the endogenous IAA content and SRD1 transcript level increased concomitantly, suggesting an involvement of SRD1 during the early stage of the auxin-dependent development of the storage root. SRD1-ox sweetpotato plants cultured in vitro produced thicker and shorter fibrous roots than wild-type plants. The metaxylem and cambium cells of the fibrous roots of SRD1-ox plants showed markedly enhanced proliferation, resulting in the fibrous roots of these plants showing an earlier thickening growth than those of wild-type plants. Taken together, these results demonstrate that SRD1 plays a role in the formation of storage roots by activating the proliferation of cambium and metaxylem cells to induce the initial thickening growth of storage roots in an auxin-dependent manner.

Effect of Pot Volume on the Growth of Sweetpotato Cultivated in the New Hydroponic System

“…Exogenous application of cytokinin also activates tuberous root formation (McDavid & Alamu, 1980;Eguchi & Yoshida, 2008). Given that SRD1, a gene which activates the development of storage roots, is highly induced by exogenous auxin treatment (Noh et al, 2010), manipulations of root hormonal levels using pharmacological treatments or environmental regulation may be employed to increase the tuberous root yield. Our hydroponic system may be effective to control root hormonal levels as the tuberous roots were grown in the small pots.…”

Recent Progress in Molecular Studies on Storage Root Formation in Sweetpotato (<i>Ipomoea batatas</i>)

“…Transgenic potato (Solanum tuberosum) plants overexpressing IbMADS1 showed a partial swelling of roots that was mainly attributed to a proliferation of metaxylem cells with thickened cell walls. Noh et al (2010) reported functional characterization of a MADS-box gene (named SRD1) that was 99% identical to IbMADS1 in the nucleotide sequence of the coding region. Expression of SRD1 was observed in the cambium cells of the developing storage roots and regulated by exogenous auxins.…”

Sweet potato expressing the rice Zn transporter <i>OsZIP4</i> exhibits high Zn content in the tuber

“…Most sweet potato is cultivated in developing countries to provide edible storage roots and foliage for humans and animals (Sihachakr and Ducreux 1987). The conventional breeding of many sweet potato varieties is complicated due to its hexaploid genome, and the incompatibility and climate restrictions for florescence (Noh et al 2010;Sihachakr and Ducreux 1987). Genetic engineering offers great potential for the quick development of new improved varieties of sweet potato.…”