Genome-Wide Identification of QTLs for Grain Protein Content Based on Genotyping-by-Resequencing and Verification of qGPC1-1 in Rice.

To clarify the genetic mechanism underlying grain protein content (GPC) and to improve rice grain qualities, the mapping and cloning of quantitative trait loci (QTLs) controlling the natural variation of GPC are very important. Based on genotyping-by-resequencing, a total of 14 QTLs were detected with the Huanghuazhan/Jizi1560 (HHZ/JZ1560) recombinant inbred line (RIL) population in 2016 and 2017. Seven of the fourteen QTLs were repeatedly identified across two years. Using three residual heterozygote-derived populations, a stably inherited QTL named as qGPC1-1 was validated and delimited to a ~862 kb marker interval JD1006-JD1075 on the short arm of chromosome 1. Comparing the GPC values of the RIL population determined by near infrared reflectance spectroscopy (NIRS) and Kjeldahl nitrogen determination (KND) methods, high correlation coefficients (0.966 and 0.983) were observed in 2016 and 2017. Furthermore, 12 of the 14 QTLs were identically identified with the GPC measured by the two methods. These results indicated that instead of the traditional KND method, the rapid and easy-to-operate NIRS was suitable for analyzing a massive number of samples in mapping and cloning QTLs for GPC. Using the gel-based low-density map consisted of 208 simple sequence repeat (SSR) and insert/deletion (InDel) markers, the same number of QTLs (fourteen) were identified in the same HHZ/JZ1560 RIL population, and three QTLs were repeatedly detected across two years. More stably expressed QTLs were identified based on the genome resequencing, which might be attributed to the high-density map, increasing the detection power of minor QTLs. Our results are helpful in dissecting the genetic basis of GPC and improving rice grain qualities through molecular assisted selection.

[Effects of exogenous growth regulators on plant elongation and carbohydrate consumption of rice seedlings under submergence.] / å¤–æºè°ƒèŠ‚å‰‚å¯¹æ·¹æ¶æ°´ç¨»å¹¼è‹—æ ªé«˜åŠç¢³æ°´åŒ–åˆç‰©æ¶ˆè€—çš„å½±å“.

This experiment was conducted to evaluate the effects of exogenous regulators on plant elongation and carbohydrate consumption of rice seedlings under submergence. IR64 and IR64-Sub1 with submergence tolerance gene Sub1 were used. Twenty-day-old seedlings were sprayed with 1-aminocyclopropane-1-carboxylic acid (ACC), paclobutrazol (PB), gibberellic acid (GA), or distilled water (as control) two days prior to the submergence. Plants were completely submerged and water depth was maintained for 0, 4, 8, 12, 16 days respectively in tanks. The plants were allowed to recover for seven days after submergence. We investigated the effects of ACC, PB, and GA on the survival percentage, shoot elongation, chlorophyll degradation and recovery, as well as non-structure carbohydrate (NSC) consumption. The results showed that complete submergence resulted in significant elongation of plant shoots, rapid decline of SPAD, and quick depletion of soluble sugars in leaves. However, the initial NSC content in shoots of IR64-Sub1 was higher than that of IR64, and the consumption rate during submergence was lower, and the starch content in shoots maintained after submergence was higher. PB could significantly enhance rice seedling survival by reducing plant elongation, chlorophyll degradation and NSC consumption, and the effect of PB pretreatment on IR64-Sub1 was more pronounced. Conversely, GA increased plant elongation, leaf chlorophyll degradation and depletion of NSC, which resulted in the lowest recovery capability and survival percentage. However, the inhibition of GA on submergence tolerance of IR64-Sub1 was much poorer compared with IR64. Plant elongation treated by ACC was much lower than by GA. In conclusion, PB could restrain plant elongation effectively, retarding chlorophyll degradation, decelerating NSC consumption and retaining more NSC after de-submergence. The results suggested that PB could increase rapid recovery of rice after submergence stress which was of significance in alleviating flood and waterlogging injury in flash-flood-prone areas.

[Response of indica rice spikelet differentiation and degeneration to air temperature and solar radiation of different sowing dates]. / ç±¼ç¨»é¢–èŠ±åˆ†åŒ–ä¸Žé€€åŒ–å¯¹ä¸åŒæ’­æœŸæ¸©å ‰çš„å“åº”.

In this study, three rice varieties, including three-line hybrid indica rice Wuyou308 and Tianyouhuazhan, and inbred indica rice Huanghuazhan were used to investigate the effects of air temperature and solar radiation on rice growth duration and spikelet differentiation and degeneration. Ten sowing-date treatments were conducted in this field experiment. The results showed that the growth duration of three indica rice varieties were more sensitive to air temperature than to day-length. With average temperature increase of 1 ℃, panicle initiation advanced 1.5 days, but the panicle growth duration had no significant correlation with the temperature and day-length. The number of spikelets and differentiated spikelets revealed significant differences among different sowing dates. Increases in average temperature, maximum temperature, minimum temperature, effective accumulated temperature, temperature gap and the solar radiation benefited dry matter accumulation and spikelet differentiation of all varieties. With increases of effective accumulated temperature, diurnal temperature gap and solar radiation by 50 ℃, 1 ℃, 50 MJ·m-2 during panicle initiation stage, the number of differentiated spikelets increased 10.5, 14.3, 17.1 respectively. The rate of degenerated spikelets had a quadratic correlation with air temperature, extreme high and low temperature aggravated spikelets degeneration, and low temperature stress made worse effect than high temperature stress. The rate of spikelet degeneration dramatically rose with the temperature falling below the critical temperature, the critical effective accumulated temperature, daily average temperature, daily maximum temperature and minimum temperature during panicle initiation were 550-600 ℃, 24.0-26.0 ℃, 32.0-34.0 ℃, 21.0-23.0 ℃, respectively. In practice, the natural condition of appropriate high temperature, large diurnal temperature gap and strong solar radiation were conducive to spikelet differentiation, and hindered the spikelet degeneration.

[Effects of low temperature on formation of spikelets and grain filling of indica inbred rice during panicle initiation in early-season].

A pot experiment in phytotron with controlled temperature was conducted to examine the effects of low temperature (LT) on differentiation and retrogression of branches and spikelets and grain filling of rice during panicle initiation (PI). In this study, indica inbred rice called Zhong-jiazaol7 was planted and treated at 17 and 20 °C of LT during primary branches anlage differentiation (II) and pollen mother cell meiosis stage (VI) of PI. The results showed that the numbers of differentiated and survived branches per panicle were significantly reduced under LT treatment compared with control, and the number of survived spikelets was significantly decreased by 7.2% - 12.4%, but the numbers of retrograded branches and spikelets were increased. Moreover, LT affected significantly the development of floral organ such as pollen activity and anther dehiscence, and caused harmful grain filling, particularly at 17 °C. The numbers of total differentiated and survived branches and spikelets were lower during VI (PI) than during II (PI) under LT stress, but more retrograded secondary branches and spikelets (increased by 11.6%) were found during V (PI) compared with II (PI). Meanwhile, in contrast to II (PI), the seed setting rate was significantly lowered by 3.7% during VI (PI), which was attributed to reductions in pollen activity, pollen grains on stigma, anther dehiscence coefficient and grain filling rate. LT stress impact on rice panicles was higher at 17 °C than at 20 °C during II and VI (PI). The cultivation measure could be correspondingly strengthened and improved in practice.

Low pH-induced changes of antioxidant enzyme and ATPase activities in the roots of rice (Oryza sativa L.) seedlings.

Soil acidification is the main problem in the current rice production. Here, the effects of low pH on the root growth, reactive oxygen species metabolism, plasma membrane functions, and the transcript levels of the related genes were investigated in rice seedlings (Oryza sativa L.) in a hydroponic system at pH 3.5, 4.5, and 5.5. There were two hybrid rice cultivars in this trial, including Yongyou 12 (YY12, a japonica hybrid) and Zhongzheyou 1 (ZZY1, an indica hybrid). Higher H+ activity markedly decreased root length, the proportion of fine roots, and dry matter production, but induced a significant accumulation of hydrogen peroxide (H2O2), and led to serious lipid peroxidation in the roots of the two varieties. The transcript levels of copper/zinc superoxide dismutase 1 (Cu/Zn SOD1), copper/zinc superoxide dismutase 2 (Cu/Zn SOD2), catalase A (CATA) and catalase B (CATB) genes in YY12 and ZZY1 roots were significantly down-regulated after low pH exposure for two weeks. Meanwhile, a significant decrease was observed in the expression of the P-type Ca2+-ATPases in roots at pH 3.5. The activities of antioxidant enzymes (SOD, CAT) and plasma membrane (PM) Ca2+-ATPase in the two varieties were dramatically inhibited by strong rhizosphere acidification. However, the expression levels of ascorbate peroxidase 1 (APX1) and PM H+-ATPase isoform 7 were up-regulated under H+ stress compared with the control. Significantly higher activities of APX and PM H+-ATPase could contribute to the adaptation of rice roots to low pH.

Proteomic identification of OsCYP2, a rice cyclophilin that confers salt tolerance in rice (Oryza sativa L.) seedlings when overexpressed.

BACKGROUND: High Salinity is a major environmental stress influencing growth and development of rice. Comparative proteomic analysis of hybrid rice shoot proteins from Shanyou 10 seedlings, a salt-tolerant hybrid variety, and Liangyoupeijiu seedlings, a salt-sensitive hybrid variety, was performed to identify new components involved in salt-stress signaling. RESULTS: Phenotypic analysis of one protein that was upregulated during salt-induced stress, cyclophilin 2 (OsCYP2), indicated that OsCYP2 transgenic rice seedlings had better tolerance to salt stress than did wild-type seedlings. Interestingly, wild-type seedlings exhibited a marked reduction in maximal photochemical efficiency under salt stress, whereas no such change was observed for OsCYP2-transgenic seedlings. OsCYP2-transgenic seedlings had lower levels of lipid peroxidation products and higher activities of antioxidant enzymes than wild-type seedlings. Spatiotemporal expression analysis of OsCYP2 showed that it could be induced by salt stress in both Shanyou 10 and Liangyoupeijiu seedlings, but Shanyou 10 seedlings showed higher OsCYP2 expression levels. Moreover, circadian rhythm expression of OsCYP2 in Shanyou 10 seedlings occurred earlier than in Liangyoupeijiu seedlings. Treatment with PEG, heat, or ABA induced OsCYP2 expression in Shanyou 10 seedlings but inhibited its expression in Liangyoupeijiu seedlings. Cold stress inhibited OsCYP2 expression in Shanyou 10 and Liangyoupeijiu seedlings. In addition, OsCYP2 was strongly expressed in shoots but rarely in roots in two rice hybrid varieties. CONCLUSIONS: Together, these data suggest that OsCYP2 may act as a key regulator that controls ROS level by modulating activities of antioxidant enzymes at translation level. OsCYP2 expression is not only induced by salt stress, but also regulated by circadian rhythm. Moreover, OsCYP2 is also likely to act as a key component that is involved in signal pathways of other types of stresses-PEG, heat, cold, or ABA.