The Shock of Shatter: Understanding Silique and Silicle Dehiscence for Improving Oilseed Crops in Brassicaceae

Abstract

Silique dehiscence, despite being an essential physiological process for seed dispersal for dehiscent fruits, is disadvantageous for the agricultural industry. While crops have been selected against the expression of natural, spontaneous shattering to protect the seeds for harvest, fruit dehiscence in the field can be promoted through abiotic factors such as wind, drought, and hail that can be detrimental in reducing crop yield and profitability. In crops like canola, pennycress, and Camelina, this impact could be as high as 50%, creating economic losses for both the industry and the economy. Mitigating the effects of fruit dehiscence is crucial to prevent seed loss, economic loss, and the persistence of volunteer plants, which interfere with crop rotation and require increased weed control. Developing agronomic traits through genetic manipulation to enhance the strength of the fruiting body can prevent seed dispersal mechanisms from occurring and boost yield efficiency and preservation. Current research into this area has created mutant plants with indehiscent fruits by reducing allele function that determines the identity of the various anatomical layers of the fruit. Future genetic approaches may focus on strengthening siliques by enhancing secondary cell walls through either increased lignification or reducing cell wall-degrading enzymes to achieve shatter tolerance. This review focuses on improving our knowledge within members of the Brassicaceae family to create a better understanding of silique/silicle dehiscence for researchers to establish a groundwork for broader applications across diverse crops. This knowledge will directly lead to improved agricultural productivity and ensure a stable food supply, addressing global challenges the world is facing.

Keywords: agriculture production; cell wall; lignification; oilseed crops; silique dehiscence; yield increases.

FIGURE 1

An illustrative figure of a silique cross‐section and B. napus cross‐section. The two images are representative of a silique cross‐section. The illustrative images are false‐colored to mimic toluidine blue O staining, with the pink/purple color representing the primary cell wall and the blue‐colored cells indicating secondary cell wall lignification. The real B. napus cross‐sections are stained with toluidine blue O. The red dotted line indicates the valve. The green dotted line indicates the lignified layer. The orange dotted line indicates the separation layer. The red line indicates the replum.

FIGURE 2

A model of Arabidopsis silique development and differentiation. The model depicts master regulatory transcription factors of silique development and differentiation, along with downstream interactions between opposing cell identity regulators creating expression gradients between the valve, valve margin, and replum. Known downstream cell wall modification enzymes and transcription factors are depicted. Solid lines indicate known pathways. Dotted lines indicate hypothetical interactions. The solid dark green line indicates the valve. The solid light green line indicates the lignified layer. The solid orange line indicates the separation layer. The solid red line indicates the replum. The silique is stained with toluidine blue O, with the pink/purple color representing the primary cell wall and the blue‐colored cells indicating secondary cell wall lignification.

FIGURE 3

An illustrative figure of a wild‐type Brassica napus silique DZ and mutant variations. The siliques are false‐colored to mimic toluidine blue O staining, with the pink/purple color representing the primary cell wall and the blue‐colored cells indicating secondary cell wall lignification (A–D). The large red arrows represent forces applied onto the silique structure (A–D). A representative wild‐type Brassica napus silique that has not undergone dehiscence (A). A representative Brassica napus wild‐type silique that has undergone dehiscence within the DZ, illustrates the separation of the valve from the replum (B). A mutant Brassica napus silique that no longer has proper cell wall and middle lamella degradation due to hypothetical knockouts in cell wall degrading enzymes (C). A mutant Brassica napus silique that no longer has secondary cell wall deposition within the endocarp b cells and lignified layer due to hypothetical knockouts in lignification deposition/patterning (D).