Polyploidization mechanisms: temperature environment can induce diploid gamete formation in Rosa sp.

Abstract

Polyploidy is an important evolutionary phenomenon but the mechanisms by which polyploidy arises still remain underexplored. There may be an environmental component to polyploidization. This study aimed to clarify how temperature may promote diploid gamete formation considered an essential element for sexual polyploidization. First of all, a detailed cytological analysis of microsporogenesis and microgametogenesis was performed to target precisely the key developmental stages which are the most sensitive to temperature. Then, heat-induced modifications in sporad and pollen characteristics were analysed through an exposition of high temperature gradient. Rosa plants are sensitive to high temperatures with a developmental sensitivity window limited to meiosis. Moreover, the range of efficient temperatures is actually narrow. 36 °C at early meiosis led to a decrease in pollen viability, pollen ectexine defects but especially the appearance of numerous diploid pollen grains. They resulted from dyads or triads mainly formed following heat-induced spindle misorientations in telophase II. A high temperature environment has the potential to increase gamete ploidy level. The high frequencies of diplogametes obtained at some extreme temperatures support the hypothesis that polyploidization events could have occurred in adverse conditions and suggest polyploidization facilitating in a global change context.

Use of 2n Gametes in Plant Breeding

“…Lokker et al (2004) exposed four complete sterile lily genotypes to heat shock treatments and observed that three of the four genotypes became fertile by the production of viable 2n gametes. Also Pécrix et al (2011) observed a production of 2n gametes up to 24.5% in Rosa spp. through an exposition of a high temperature gradient, but the range of efficient temperatures is narrow and should be applied during early meiosis.…”

“…Moreover, frequencies may vary in different populations, within a certain genotype and during time (season) due to environmental fluctuations (Bani-Aameur et al, 1992;Crespel et al, 2006;McCoy, 1982;Ortiz et al, 1998;Ortiz & Vulsteke, 1995;Parrott & Smith, 1984;Pécrix et al, 2011;Veilleux et al, 1982). In Table 2, some recently published data on 2n gamete frequency in different (hybrid and non hybrid) populations are given.…”

Plant germline formation: common concepts and developmental flexibility in sexual and asexual reproduction

“…For example, in rose (Rosa spp.) short periods of heat stress result in partial restitution of male meiosis and the formation of unreduced dyads, but also triads and polyads (Pecrix et al, 2011). Analysis of the effect of redox status on germline specification in maize revealed another link to abiotic stress.…”

Production of Diploid Male Gametes in Arabidopsis by Cold-Induced Destabilization of Postmeiotic Radial Microtubule Arrays

“…Similarly, in rose (Rosa spp. ), short periods of high temperature (48 h at 30°C-36°C) can induce cytomixis and parallel and tripolar spindles at male metaphase II, generating dyads and triads at the end of male sporogenesis (Pécrix et al, 2011). Low-temperature environments can also stimulate 2n gamete formation.…”