Large changes in anatomy and physiology between diploid Rangpur lime (Citrus limonia) and its autotetraploid are not associated with large changes in leaf gene expression

Abstract

Very little is known about the molecular origin of the large phenotypic differentiation between genotypes arising from somatic chromosome set doubling and their diploid parents. In this study, the anatomy and physiology of diploid (2x) and autotetraploid (4x) Rangpur lime (Citrus limonia Osbeck) seedlings has been characterized. Growth of 2x was more vigorous than 4x although leaves, stems, and roots of 4x plants were thicker and contained larger cells than 2x that may have a large impact on cell-to-cell water exchanges. Leaf water content was higher in 4x than in 2x. Leaf transcriptome expression using a citrus microarray containing 21 081 genes revealed that the number of genes differentially expressed in both genotypes was less than 1% and the maximum rate of gene expression change within a 2-fold range. Six up-regulated genes in 4x were targeted to validate microarray results by real-time reverse transcription-PCR. Five of these genes were apparently involved in the response to water deficit, suggesting that, in control conditions, the genome expression of citrus autotetraploids may act in a similar way to diploids under water-deficit stress condition. The sixth up-regulated gene which codes for a histone may also play an important role in regulating the transcription of growth processes. These results show that the large phenotypic differentiation in 4x Rangpur lime compared with 2x is not associated with large changes in genome expression. This suggests that, in 4x Rangpur lime, subtle changes in gene expression may be at the origin of the phenotypic differentiation of 4x citrus when compared with 2x.

Effect of polyploidization on morphology in two apple (Malus × domestica) genotypes

“…leaf colour and anatomy in Citrus spp. (Allario et al 2011), leaf anatomy in Lonicera ), cell anatomy in Lolium (Sugiyama 2005) and leaf morphology and colour in Rosa (Kermani et al 2003). The variation in leaf colour in our study could be significantly correlated with the pigment concentration per mm² leaf area.…”

“…apple (Lespinasse, Noiton 1986;Blanke et al 1994), Populus (Cohen et al 2010), Citrus spp. (Allario et al 2011) and Arabidopsis (Del Pozo, RamirezParra 2014). The increase in guard cell length, decrease in stomatal density and increase in overall cell size proves to be strongly correlated with an increase in genome size; this seems to be a general observation in plants (Beaulieu et al 2008).…”

“…Morphological effects commonly associated with polyploidy are bigger flowers, an altered leaf length-to-width ratio and changes in size and density of stomata (Sun et al 2009;Van Laere et al 2011;Trojak-Goluch, Skomra 2013;Tan et al 2015). Other frequently occurring characteristics include darker-coloured green leaves and a more compact growth habit (Kermani et al 2003;Liu et al 2007;Allario et al 2011).…”

Enhanced Stomatal Conductance by a Spontaneous Arabidopsis Tetraploid, Me-0, Results from Increased Stomatal Size and Greater Stomatal Aperture

“…These differences related to ABA responsiveness seem to affect stomatal aperture between Me-0 and tetraploid Col. del Pozo and Ramirez-Parra (2014) reported that not only tetraploid Arabidopsis Col but also the Landsberg erecta ecotype have smaller stomatal apertures and exhibit differential expression of genes involved in ABA metabolism, compared with their diploid relatives. Tetraploids of another plant species, Rangpur lime, also alter the expression of ABA-related genes and accumulate excessive ABA, thereby decreasing g s (Allario et al, 2011(Allario et al, , 2013. These reports support the possibility that increasing the ploidy level in some ecotypes and plant species changes ABA responsiveness or biosynthesis; however, tetraploidization does not always affect ABA responsiveness or induce an equal effect on ABA responsiveness, as in Me-0 and tetraploid Col.…”

“…In addition to the negative effects of large stomata on gas exchange , polyploids may have another disadvantage; del Pozo and Ramirez-Parra (2014) showed that artificially induced tetraploids of Arabidopsis have a reduced stomatal density (stomatal number per unit of leaf area) and a lower stomatal index (stomatal number per epidermal cell number). Moreover, tetraploids of Rangpur lime (Citrus limonia) and Arabidopsis have lower transpiration rates and changes in the expression of genes involved in abscisic acid (ABA), a phytohormone that induces stomatal closure (Allario et al, 2011;del Pozo and RamirezParra, 2014). On the other hand, an increase in the ploidy level of Festuca arundinacea results in an increase in the CO 2 -exchange rate (Byrne et al, 1981); hence, polyploids may not necessarily have a reduced gasexchange capacity.…”