Grain shattering by cell death and fracture in Eragrostis tef

Abstract

Abscission, known as shattering in crop species, is a highly regulated process by which plants shed parts. Although shattering has been studied extensively in cereals and a number of regulatory genes have been identified, much diversity in the process remains to be discovered. Teff (Eragrostis tef) is a crop native to Ethiopia that is potentially highly valuable worldwide for its nutritious grain and drought tolerance. Previous work has suggested that grain shattering in Eragrostis might have little in common with other cereals. In this study, we characterize the anatomy, cellular structure, and gene regulatory control of the abscission zone (AZ) in E. tef. We show that the AZ of E. tef is a narrow stalk below the caryopsis, which is common in Eragrostis species. X-ray microscopy, scanning electron microscopy, transmission electron microscopy, and immunolocalization of cell wall components showed that the AZ cells are thin-walled and break open along with programmed cell death at seed maturity, rather than separating between cells as in other studied species. Knockout of YABBY2/SHATTERING1, documented to control abscission in several cereals, had no effect on abscission or AZ structure in E. tef. RNA sequencing analysis showed that genes related to programmed cell death and cell wall modification are enriched in the AZ at the early seed maturity stage. These data show that E. tef drops its seeds using a unique mechanism. Our results provide the groundwork for understanding grain shattering in Eragrostis and further improvement of shattering in E. tef.

The YABBY gene SHATTERING1 controls activation rather than patterning of the abscission zone in Setaria viridis

“…Samples for TEM were prepared as described in Yu et al . (2023) with modifications. Briefly, AZs at 31 and 38 d were dissected and fixed in 2% (w/v) PFA and 2% (w/v) glutaraldehyde with 0.1% (v/v) Tween 20 in 0.1 M cacodylate buffer at pH 7.4 overnight at 4°C and postfixed in 1% (w/v) osmium tetroxide in cacodylate buffer for 3 h, followed by 1% (w/v) aqueous uranyl acetate at 4°C overnight and then 50°C for 2 h. Samples were dehydrated in a graded acetone series and embedded in Quetol 651 epoxy resin at 60°C for 48 h. Samples were sectioned at 60 nm using a Leica Ultracut UCT ultramicrotome, mounted on formvar/carbon film on slotted gold grids (FCF2010‐Au‐SB; Electron Microscopy Sciences, Hatfield, PA, USA), stained with lead citrate for 8 min and imaged using a Talos L 120C G2 with a CETA 16 M 4 K × 4 K CMOS camera (Thermo Fisher Scientific), and tile mapped with 2 s exposure time using M aps 3 software (v.3.16) at 8500× (pixel size 1.72 nm) and with V elox (Release 3.1) at 17 500× or 22 000× magnifications.…”

“…Cell wall immunofluorescence followed the procedure described in Yu et al . (2023). To calculate average wall intensity for each probe, the probe signal in the AZ was divided by the area of cell wall autofluorescence using F iji (v.2.9.0; Schindelin et al ., 2012).…”

“…senescence) or environmental (biotic and abiotic stresses) cues, abscission initiates by activating cell wall hydrolytic enzymes and degrading the cell wall, mainly the middle lamella, leading to cell separation (Patterson, 2001; Kim, 2014). Programmed cell death is also observed during abscission in some species (Bar‐Dror et al ., 2011; Yu et al ., 2023).…”