Transcriptomic Analysis Reveals a Comprehensive Calcium- and Phytohormone-Dominated Signaling Response in Leymus chinensis Self-Incompatibility.

Shuangyan Chen,Pincang Zhao,Gongshe Liu,Liqin Cheng,Xiaoxia Li,Junting Jia,Xiaobing Dong,Dongmei Qi,Hui Liu,Weiguang Yang

doi:10.3390/ijms20092356

Abstract

Sheepgrass (Leymus chinensis (Trin.) Tzvel.) is an economically and ecologically important forage in the grass family. Self-incompatibility (SI) limits its seed production due to the low seed-setting rate after self-pollination. However, investigations into the molecular mechanisms of sheepgrass SI are lacking. Therefore, microscopic observation of pollen germination and pollen tube growth, as well as transcriptomic analyses of pistils after self- and cross-pollination, were performed. The results indicated that pollen tube growth was rapidly inhibited from 10 to 30 min after self-pollination and subsequently stopped but preceded normally after cross-pollination. Time course comparative transcriptomics revealed different transcriptome dynamics between self- and cross-pollination. A pool of SI-related signaling genes and pathways was generated, including genes related to calcium (Ca2+) signaling, protein phosphorylation, plant hormone, reactive oxygen species (ROS), nitric oxide (NO), cytoskeleton, and programmed cell death (PCD). A putative SI response molecular model in sheepgrass was presented. The model shows that SI may trigger a comprehensive calcium- and phytohormone-dominated signaling cascade and activate PCD, which may explain the rapid inhibition of self-pollen tube growth as observed by cytological analyses. These results provided new insight into the molecular mechanisms of sheepgrass (grass family) SI.

Highlights

About 40% of flowering plant species and at least 100 families have self-incompatibility (SI)
The results showed that 70% of the pollen grains normally germinated at 5 min after self- and cross-pollination, and this number reached 88% to 90% at 30 min and remained stable at over 90% (Figure 1)
258 (167 upregulated and 91 downregulated), 1326 (1041 upregulated and 285 downregulated), and 9909 (6097 upregulated and 3812 downregulated) Differentially expressed gene (DEG) were detected in cross-pollination at 5 min, 10 min, and 30 min, respectively (Figure 3B,C). These results indicated that many DEGs were rapidly induced at 5 min after self-pollination compared to cross-pollination, in which many DEGs were induced at 30 min

Summary

Introduction

About 40% of flowering plant species and at least 100 families have self-incompatibility (SI). Each S-locus F-box (SLF) protein interacts with one or more S-RNase proteins that are not their own S-haplotypes, called collaborative nonself-recognition, and S-RNase proteins are detoxified via a ubiquitin proteasome pathway [1,9,10]. Papaver rhoeas is another well-characterized GSI system. The cognate interaction of the female determinant, PrsS, and the male S-determinant, PrpS, triggers Ca2+ signaling cascades and protein phosphorylation, subsequently altering the cytoskeleton and initiating programmed cell death (PCD) in incompatible pollen [11,12,13,14,15,16]. Additional factors are involved in SI response, including the E3 ubiquitin ligase arm repeat containing 1 (ARC1) [24], M-locus protein kinase (MLPK) [25], and thioredoxin h-like 1 (THL1) [26]

Methods

Results

Discussion

Conclusion