HWA1- and HWA2-Mediated Hybrid Weakness in Rice Involves Cell Death, Reactive Oxygen Species Accumulation, and Disease Resistance-Related Gene Upregulation

Abstract

Hybrid weakness is a type of reproductive isolation in which F1 hybrids of normal parents exhibit weaker growth characteristics than their parents. F1 hybrid of the Oryza sativa Indian cultivars ‘P.T.B.7′ and ‘A.D.T.14′ exhibits hybrid weakness that is associated with the HWA1 and HWA2 loci. Accordingly, the aim of the present study was to analyze the hybrid weakness phenotype of the ‘P.T.B.7′ × ‘A.D.T.14′ hybrids. The height and tiller number of the F1 hybrid were lower than those of either parent, and F1 hybrid also exhibited leaf yellowing that was not observed in either parent. In addition, the present study demonstrates that SPAD values, an index correlated with chlorophyll content, are effective for evaluating the progression of hybrid weakness that is associated with the HWA1 and HWA2 loci because it accurately reflects degree of leaf yellowing. Both cell death and H2O2, a reactive oxygen species, were detected in the yellowing leaves of the F1 hybrid. Furthermore, disease resistance-related genes were upregulated in the yellowing leaves of the F1 hybrids, whereas photosynthesis-related genes tended to be downregulated. These results suggest that the hybrid weakness associated with the HWA1 and HWA2 loci involves hypersensitive response-like mechanisms.

Mix‐cropping of rice and water mimosa (Neptunia oleracea Lour.) increases rice photosynthetic efficiency, yield, grain quality and soil available nutrients

“…It is acknowledged that height, tiller number and chlorophyll content are important indicators of rice growth conditions. 29,30 In the present study, rice growth characteristics were significantly improved in the intercropping and mix-cropping treatments compared with those in the monocropping treatment (Fig. 3).…”

“…In this study, rice and water mimosa were cultivated in three patterns (monocropping, intercropping and mix‐cropping), and the growth attributes of rice were examined. It is acknowledged that height, tiller number and chlorophyll content are important indicators of rice growth conditions 29,30 . In the present study, rice growth characteristics were significantly improved in the intercropping and mix‐cropping treatments compared with those in the monocropping treatment (Fig.…”

Parental Genome Imbalance Causes Hybrid Seed Lethality as Well as Ovary Abscission in Interspecific and Interploidy Crosses in Nicotiana

“…Conspecific pollen precedence and gametic incompatibility are examples of post-mating prezygotic isolating barriers ( Rieseberg and Willis, 2007 ). In turn, postzygotic isolation barriers include enlarged ovary (immature fruit) abscission ( Gupta et al, 1996 ; He et al, 2019 ), seed abortion or hybrid seed lethality ( Coughlan et al, 2020 ; Dziasek et al, 2021 ), hybrid weakness ( Shiragaki et al, 2019 , 2020 ), hybrid lethality ( Kawaguchi et al, 2021 ; Si et al, 2021 ; Tezuka et al, 2021 ; Mino et al, 2022 ), and hybrid sterility ( Li et al, 2020 ) in seedlings of the F 1 generation, as well as hybrid breakdown recognized in generations after the F 1 ( Matsubara et al, 2007 ; Zhang et al, 2021 ). These isolating barriers may be observed independently or combined, even in a single cross-combination.…”

A Novel Combination of Genes Causing Temperature-Sensitive Hybrid Weakness in Rice

“…This result should be carefully translated because RNA was extracted from the aerial part of young seedlings where no symptom was observed. To date, several studies have shown that the activation of PR genes is associated with the occurrence of symptoms under various types of conditions ( Yamamoto et al, 2010 ; Chen et al, 2014 ; Shiragaki et al, 2019 ). Therefore, sampling factors such as growth stage and organ source must be taken into consideration.…”