Dominance and Sexual Dimorphism Pervade the Salix purpurea L. Transcriptome

Abstract

The heritability of gene expression is critical in understanding heterosis and is dependent on allele-specific regulation by local and remote factors in the genome. We used RNA-Seq to test whether variation in gene expression among F1 and F2 intraspecific Salix purpurea progeny is attributable to cis- and trans-regulatory divergence. We assessed the mode of inheritance based on gene expression levels and allele-specific expression for F1 and F2 intraspecific progeny in two distinct tissue types: shoot tip and stem internode. In addition, we explored sexually dimorphic patterns of inheritance and regulatory divergence among F1 progeny individuals. We show that in S. purpurea intraspecific crosses, gene expression inheritance largely exhibits a maternal dominant pattern, regardless of tissue type or pedigree. A significantly greater number of cis- and trans-regulated genes coincided with upregulation of the maternal parent allele in the progeny, irrespective of the magnitude, whereas the paternal allele was higher expressed for genes showing cis × trans or compensatory regulation. Importantly, consistent with previous genetic mapping results for sex in shrub willow, we have delimited sex-biased gene expression to a 2 Mb pericentromeric region on S. purpurea chr15 and further refined the sex determination region. Altogether, our results offer insight into the inheritance of gene expression in S. purpurea as well as evidence of sexually dimorphic expression which may have contributed to the evolution of dioecy in Salix.

A willow sex chromosome reveals convergent evolution of complex palindromic repeats

“…This is quite different from the closely related genus Populus where sex-determining regions consistently occur on chromosome 19, with most species showing male heterogamety [23,24]. Previously, we reported that the SDR occupies a large portion of the W chromosome in S. purpurea with suppressed recombination extending over~5 Mb [20,25]. This is substantially larger than the SDR in P. trichocarpa and P. balsamifera, which appears to be approximately 100 kb in size [24,26].…”

The Guppy Sex Chromosome System and the Sexually Antagonistic Polymorphism Hypothesis for Y Chromosome Recombination Suppression

“…SA effects are plausible [ 19 ], including in animals in which sexual selection occurs, or similar differences in investment in attractiveness to pollinators by male plants versus females [ 20 ]. Levels of expression of many genes may differ in the two sexes of animals [ 21 ] and plants [ 22 , 23 , 24 ], supporting the idea that the two sexes have different evolutionary optima for expression. However, SA polymorphisms establish only under restricted conditions [ 25 ], and empirical tests are needed to find out whether such polymorphisms indeed occur and are maintained long enough to cause the effects proposed in theoretical models.…”

A Willow Sex Chromosome Reveals Convergent Evolution of Complex Palindromic Repeats

“…This is quite different from the closely-related genus Populus where sex determining regions consistently occur on chromosome 19, with most species showing male heterogamety [21, 22]. Previously, we reported that the SDR occupies a large portion of the W chromosome in S. purpurea , because a large region on Chr15 shows lack of recombination and a large number of female-biased alleles [18, 23]. This is different from the small SDR observed in P. trichocarpa and P. balsamifera [22, 24].…”