Histological Characteristics, Cell Wall Hydrolytic Enzymes Activity and Candidate Genes Expression Associated with Seed Shattering of Elymus sibiricus Accessions.

Xuhong Zhao,Zongyu Zhang,Yanrong Wang,Wengang Xie,Junchao Zhang

doi:10.3389/fpls.2017.00606

Abstract

Elymus sibiricus (siberian wildrye) is a perennial, cool-season, self-pollinating, and allotetraploid grass. As an economically important species, it has been widely grown and used for pasture and hay in northern China. Because of serious seed shattering (SS), however, E. sibiricus is difficult to grow for commercial seed production. To better understand the underlying mechanism of SS, we investigated the differences in SS of cultivars and wild accessions in relation to morphological and genetic diversity, histological characteristics, lignin staining, cell wall hydrolytic enzymes activity and candidate genes expressions. We found high level of morphological and genetic diversity among E. sibiricus accessions. In general, cultivars had higher average pedicel breaking tensile strength (BTS) value than wild accessions, of which PI655199 had the highest average BTS value (144.51 gf) and LQ04 had the lowest average BTS value (47.17 gf) during seed development. SS showed a significant correlation with seed length, awn length and 1000-seed weight. SS was caused by degradation of abscission layers that formed at early heading stage, and degradation of abscission layers occurred at 14 days after heading. Histological analysis of abscission zone (AZ) showed a smooth fracture surface on the rachilla in high SS genotype, suggesting higher degradation degree of abscission layers. This may resulted from the increased cellulase and polygalacturonase activity found in AZ at seed physiological maturity. Staining of pedicels of two contrasting genotypes suggested more lignin deposition in low SS genotype may play a role in resistance of SS. Furthermore, candidate genes that involved in cell wall-degrading enzyme and lignin biosynthesis were differentially expressed in AZ, indicating the involvement and role in SS. This study provided novel insights into the mechanism of SS in E. sibiricus.

Highlights

Seed shattering (SS) is an important adaptive trait for the efficient propagation of offspring in wild plants, but is a major cause of yield loss in crops (Dong and Wang, 2015)
The greatest morphological variation was found for SS (CV = 64.55%), followed by seed width (SW) (CV = 45.89%), 1000-seed weight (KW) (CV = 40.85%), awn length (AL) (CV = 21.76%) and seed length (SL) (CV = 14.19%) (Table 2)
There was a decline of pedicel breaking tensile strength (BTS) at 7 days after heading (DAH) for wild accessions, BTS value of cultivars maintained generally a stable level from 0 DAH to 14 DAH

Summary

Introduction

Seed shattering (SS) is an important adaptive trait for the efficient propagation of offspring in wild plants, but is a major cause of yield loss in crops (Dong and Wang, 2015). During early domestication of grass species (e.g., rice, wheat and barley), loss of SS is considered to be one of the most important traits (Fuller, 2007). As an economically important species, E. sibiricus has been widely grown and used for pasture and hay, owing to its excellent stress tolerance, good forage quality and adaptability to local environment (Xie et al, 2015). Previous study showed shattering can cause up to 80% yield losses if harvesting is delayed (You et al, 2011). The average seed production is only 690 kg·ha−1 due to SS (China Grass Internet, 2013). Selection for seed retention and improvement of SS in this species are, strongly recommended

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