Annals of Botany

Rye B chromosomes and heat tolerance in microsporogenesis

Rye supernumerary (B) chromosomes possess an accumulation mechanism involving the subtelomeric domain enriched by B chromosome specific DNA sequence families, D1100 and E3900. Pereira et al. show that presence of rye B chromosomes may protect pollen mother cells at meiosis against heat stress induced damage.

Dynamics of tE3900 (red) and D1100 (green) throughout pre-meiotic interphase and prophase I in 2B plants grown in control conditions.
Dynamics of tE3900 (red) and D1100 (green) throughout pre-meiotic interphase and prophase I in 2B plants grown in control conditions. (A) PMI showing E3900 and D1100 domains partially decondensed in Rabl configuration. (B) (i) Leptotene with D1100 and E3900 B sub-telomeric domains associated with clustered telomeric heterochromatin, (ii) black and white image and (iii) schematic representation showing a striking extension of well-resolved chromosome fibres corresponding to B regions enriched in D1100 and E3900 from the telomeric heterochromatic cluster towards the opposite cell pole. (C) (i) Pachytene with paired B D1100/E3900-enriched regions evident as single extended FISH signals containing two distinct D1100 domains. (ii) High-resolution images of paired pachytene B chromosomes show tE3900 overlapping with the condensed blocks of the proximal D1100 domain and its complete absence in D1100 gaps. The distal D1100 region is highly enriched in both 2·7- and 3·9-kb E3900 variants and is consistently decondensed in a homogeneous manner. (D) Diakinesis with highly condensed D1100 and E3900 signals visible on commonly early resolved B chromosomes. (E) Schematic representation of dynamics in the condensation state of D1100- and E3900-enriched regions in early prophase I. D1100-rich/E3900-poor region is represented in green and D1100/E3900-rich region in red. Condensed mitotic metaphase B chromosome is presented as a reference. (F,G) Pachytene nuclei from a plant with two B chromosomes with a large deletion in the distal extended domain (2B-del). (F) Nucleus showing overlapping of tE3900 (red) and E3900 (yellow). (G) Nucleus showing the proximal condensed D1100 blocks (green) and interstitial regions, which appear intact, together with tE3900 (red). Scale bar = 10 μm.

Heat resulted in equal up-regulation of heat shock protein Hsp101 transcripts in plants with zero or 2B chromosomes. A significant up-regulation of E3900 related transcripts occurred in 2B plants at meiotic prophase I, compared to in 0B plants that showed significantly greater heat induced nuclear anomalies. Bioinformatics revealed a high density of known heat responsive cis-regulatory elements within the E3900 sequence and a truncated variant, supporting stress induced response of transcription and a role for B chromosomes in the protection against heat stress induce damage.


Pereira, H. S., Delgado, M., Viegas, W., Rato, J. M., Barão, A., & Caperta, A. D. (2016). Rye (Secale cereale) supernumerary (B) chromosomes associated with heat tolerance during early stages of male sporogenesis. Annals of Botany, 119(3), 325–337.

About the author

Annals of Botany Office

The Annals of Botany Office is based at the University of Oxford.