Unraveling the Genetic Architecture of Two Complex, Stomata-Related Drought-Responsive Traits by High-Throughput Physiological Phenotyping and GWAS in Cowpea (Vigna. Unguiculata L. Walp).

Xinyi Wu,Wenzhao Xu,Pei Xu,Jian Wang,Xiaohua Wu,Ting Sun,Guojing Li,Ying Wang,Yanwei Li,Baogen Wang,Zhongfu Lu,Yudong Sun

doi:10.3389/fgene.2021.743758

Abstract

Drought is one of the most devasting and frequent abiotic stresses in agriculture. While many morphological, biochemical and physiological indicators are being used to quantify plant drought responses, stomatal control, and hence the transpiration and photosynthesis regulation through it, is of particular importance in marking the plant capacity of balancing stress response and yield. Due to the difficulties in simultaneous, large-scale measurement of stomatal traits such as sensitivity and speed of stomatal closure under progressive soil drought, forward genetic mapping of these important behaviors has long been unavailable. The recent emerging phenomic technologies offer solutions to identify the water relations of whole plant and assay the stomatal regulation in a dynamic process at the population level. Here, we report high-throughput physiological phenotyping of water relations of 106 cowpea accessions under progressive drought stress, which, in combination of genome-wide association study (GWAS), enables genetic mapping of the complex, stomata-related drought responsive traits “critical soil water content” (θcri) and “slope of transpiration rate declining” (KTr). The 106 accessions showed large variations in θcri and KTr, indicating that they had broad spectrum of stomatal control in response to soil water deficit, which may confer them different levels of drought tolerance. Univariate GWAS identified six and fourteen significant SNPs associated with θcri and KTr, respectively. The detected SNPs distributed in nine chromosomes and accounted for 8.7–21% of the phenotypic variation, suggesting that both stomatal sensitivity to soil drought and the speed of stomatal closure to completion were controlled by multiple genes with moderate effects. Multivariate GWAS detected ten more significant SNPs in addition to confirming eight of the twenty SNPs as detected by univariate GWAS. Integrated, a final set of 30 significant SNPs associated with stomatal closure were reported. Taken together, our work, by combining phenomics and genetics, enables forward genetic mapping of the genetic architecture of stomatal traits related to drought tolerance, which not only provides a basis for molecular breeding of drought resistant cultivars of cowpea, but offers a new methodology to explore the genetic determinants of water budgeting in crops under stressful conditions in the phenomics era.

Highlights

Water deficiency caused by soil drought is one of the most severe agricultural problems affecting plant growth and crop yield globally (Gupta et al, 2020)
Plants were grown under identical ambient environmental condition and subject to the same progressive soil drought treatment imposed by water withholding, which mimicked natural field drought
The KTrassociated SNPs were located on chromosomes Vu01, Vu03, Vu04, Vu05, Vu07, Vu08, Vu09 and Vu11, each explaining 9.1–13.2% of the phenotypic variation. These results indicate that both stomatal sensitivity to soil drought and the speed of stomatal closure to completion in cowpea were controlled by multiple genes with moderate effects

Summary

Introduction

Water deficiency caused by soil drought is one of the most severe agricultural problems affecting plant growth and crop yield globally (Gupta et al, 2020). In Arabidopsis, rice, and other plants, many drought-inducible genes with various functions have been identified, involving different molecular responses and gene pathways (Shinozaki and Yamaguchi-Shinozaki, 2007; Park et al, 2015; Wang et al, 2019; Gupta et al, 2020). The Harpin-encoding gene hrf, the RING-finger containing E3 ligase OsSDIR1 modulate stomatal closure and enhance drought tolerance in rice (Gao et al, 2011; Zhang et al, 2011; You et al, 2013), the ABA receptors PYR/PYL/RCAR and SNF1related protein kinases (SnRK2 kinases) could improve water use efficiency in A. thaliana (Park et al, 2015; Wang et al, 2019).

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