Molecular mechanisms of heterosis under drought stress in maize hybrids Zhengdan7137 and Zhengdan7153

Abstract

Maize is one of the most successful crops in utilizing heterosis which significantly improves maize stresses resistance and yield. Drought is a destructive abiotic stress that significantly reduces crop yield, particularly in maize. Drought stress and re-watering frequently occur during the growth and development of maize; however, the molecular mechanisms of heterosis under drought stress and re-watering have rarely been systematically investigated. Zhengdan7137 and Zhengdan7153 are two maize hybrid varieties with robust heterosis, and separately belongs to the SS×NSS and Reid×Tangsipingtou heterotic groups. 54 transcriptomes of these two hybrids and their parental inbred lines were analyzed under well-watering (WW), water-deficit (WD), and re-watering (RW) conditions using RNA-Seq. In this study, we identified 3,411 conserved drought response genes (CDRGs) and 3,133 conserved re-watering response genes (CRRGs) between Zhengdan7137 and Zhengdan7153. When comparing CDRGs and CRRGs to overdominance and underdominance genes, we identified 303 and 252 conservative drought response overdominance genes (DODGs) and underdominance genes (DUDGs), respectively, and 165 and 267 conservative re-watering response overdominance genes (RODGs) and underdominance genes (RUDGs), respectively. DODGs are involved in stress response-related processes, such as L-phenylalanine metabolism, carbohydrate metabolism, and heat response, whereas DUDGs are associated with glucose metabolism, pentose-phosphate shunt, and starch metabolism. RODGs and RUDGs contribute to the recovery of hybrids from drought stress by upregulating cell propagation and photosynthesis processes, and repressing stress response processes, respectively. It indicated overdominant and underdominant genes conservatively contributed to hybrid heterosis under drought stress. These results deepen our understanding of the molecular mechanisms of drought resistance, uncover conservative molecular mechanisms of heterosis under drought stress and re-watering, and provide potential targets for improving drought resistance in maize.

Keywords: RNA-Seq; drought; heterosis; maize; overdominant genes; re-watering; underdominant genes.

Figure 1

Kernels water content (A) and grain yield per ear (B) of AB, CD and their parental inbred lines under well-watering (WW) and water-deficit (WD) conditions. KWC, kernels water content; GY, grain yield per ear; “*”, “**” and ns, p-value<0.05, <0.01 and >0.05 in student’s t test, respectively. AB, hybrid Zhengdan7137; AA, inbred line Zheng1110; BB, inbred line Zheng1117. AA and BB are parental inbred lines of AB. CD, hybrid Zhengdan7153; CC, inbred line Zheng1121; DD, inbred line Zheng641. CC and DD are parental inbred lines of CD.

Figure 2

The Pearson correlation rate analysis of RNA-Seq libraries of AB, CD and their parental inbred lines under WW, WD and RW conditions. (A) the biological repeates of RNA-Seq libraries were high related in the Pearson correlation rate ananlysis; (B) Pearson correlation rates between WW, WD and RW conditions of hybrid AB (middle) were significant lower than its parental inbred lines AA (left) and BB (right); (C) RNA-Seq librarys of hybrids AB and CD were highly correlated under WW, WD and RW conditions. AB, hybrid Zhengdan7137; AA, inbred line Zheng1110; BB, inbred line Zheng1117. AA and BB are parental inbred lines of AB. CD, hybrid Zhengdan7153; CC, inbred line Zheng1121; DD, inbred line Zheng641. CC and DD are parental inbred lines of CD.

Figure 3

Drought response genes of hybrids AB, CD and their parental inbred lines. (A, B) venn diagrams of drought response genes in AB, AA and BB (A), and CD, CC, and DD (B); (C) venn diagrams of drought response genes of AB and CD; (D), top 30 enrichment terms in GO analysis of up- and down- regulated CDRGs; (E), top 20 enrichment terms in KEEG pathways analysis of up- (left) and down- (right) regulated CDRGs. AB, hybrid Zhengdan7137; AA, inbred line Zheng1110; BB, inbred line Zheng1117. AA and BB are parental inbred lines of AB. CD, hybrid Zhengdan7153; CC, inbred line Zheng1121; DD, inbred line Zheng641. CC and DD are parental inbred lines of CD.

Figure 4

Genes expression patterns of hybrids Zhengdan7137 (AB) and Zhengdan7153 (CD) under well-watering (WW), water-deficited (WD) and re-watering (RW) conditions. (A, B) genes in PAV related expression patterns of AB (A) and CD (B). AB and CD, Zhengdan7137 and Zhengdan7153. WW, WD and RW, well-watering, water-deficited and re-watering conditions; I, II, III, IV, and V were co-expression in both parents but not expression in hybrids genes (type I), only one parent specifically expressed genes (type II), hybrids specifically expressed genes (type III), hybrids and one specific parent expressed genes (type IV), and both parent and hybrid co-expression genes (type V); (C, D) nonadditive expression genes of AB (C) and CD (D). AB, hybrid Zhengdan7137; AA, inbred line Zheng1110; BB, inbred line Zheng1117. AA and BB are parental inbred lines of AB. CD, hybrid Zhengdan7153; CC, inbred line Zheng1121; DD, inbred line Zheng641. CC and DD are parental inbred lines of CD.

Figure 5

GO and KEGG analysis of DODGs and DUDGs. (A, B) the top 30 GO enrichment terms for DODGs and DUDGs; (C, D) the top 20 KEGG enrichment terms for DODGs and DUDGs.

Figure 6

qRT-PCR for overdominant genes. ZmGAPDH was used as the internal reference. AB, hybrid Zhengdan7137; AA, inbred line Zheng1110; BB, inbred line Zheng1117. AA and BB are parental inbred lines of AB. CD, hybrid Zhengdan7153; CC, inbred line Zheng1121; DD, inbred line Zheng641. CC and DD are parental inbred lines of CD.