A cellular mechanism underlying the restoration of thermo/photoperiod-sensitive genic male sterility.

During anther development, the transformation of the microspore into mature pollen occurs under the protection of first the tetrad wall and later the pollen wall. Mutations in genes involved in this wall transition often lead to microspore rupture and male sterility; some such mutants, such as the reversible male sterile (rvms) mutant, are thermo/photoperiod-sensitive genic male sterile (P/TGMS) lines. Previous studies have shown that slow development is a general mechanism of P/TGMS fertility restoration. In this study, we identified restorer of rvms-2 (res2), which is an allele of QUARTET 3 (QRT3) encoding a polygalacturonase that shows delayed degradation of the tetrad pectin wall. We found that MS188, a tapetum-specific transcription factor essential for pollen wall formation, can activate QRT3 expression for pectin wall degradation, indicating a non-cell-autonomous pathway involved in the regulation of the cell wall transition. Further assays showed that a delay in degradation of the tetrad pectin wall is responsible for the fertility restoration of rvms and other P/TGMS lines, whereas early expression of QRT3 eliminates low temperature restoration of rvms-2 fertility. Taken together, these results suggest a likely cellular mechanism of fertility restoration in P/TGMS lines, that is, slow development during the cell wall transition of P/TGMS microspores may reduce the requirement for their wall protection and thus support their development into functional pollens, leading to restored fertility.

OsMS188 Is a Key Regulator of Tapetum Development and Sporopollenin Synthesis in Rice.

BACKGROUND: During anther development, the tapetum provides essential nutrients and materials for pollen development. In rice, multiple transcription factors and enzymes essential for tapetum development and pollen wall formation have been cloned from male-sterile lines. RESULTS: In this study, we obtained several lines in which the MYB transcription factor OsMS188 was knocked out through the CRISPR-Cas9 approach. The osms188 lines exhibited a male-sterile phenotype with aberrant development and degeneration of tapetal cells, absence of the sexine layer and defective anther cuticles. CYP703A3, CYP704B2, OsPKS1, OsPKS2, DPW and ABCG15 are sporopollenin synthesis and transport-related genes in rice. Plants with mutations in these genes are male sterile, with a defective sexine layer and anther cuticle. Further biochemical assays demonstrated that OsMS188 binds directly to the promoters of these genes to regulate their expression. UDT1, OsTDF1, TDR, bHLH142 and EAT1 are upstream regulators of rice tapetum development. Electrophoretic mobility shift assays (EMSAs) and activation assays revealed that TDR directly regulates OsMS188 expression. Additionally, protein interaction assays indicated that TDR interacts with OsMS188 to regulate downstream gene expression. CONCLUSION: Overall, OsMS188 is a key regulator of tapetum development and pollen wall formation. The gene regulatory network established in this work may facilitate future investigations of fertility regulation in rice and in other crop species.

[Effects of thinning and reshaping on canopy micro-domain environment and leaf physiological characteristics in dense Fuji apple orchard on Loess Plateau of eastern Gansu, China]. / é—´ä¼æ”¹å½¢å¯¹é™‡ä¸œé«˜åŽŸå¯†é—­å¯Œå£«è‹¹æžœå›­å† å±‚å¾®åŸŸçŽ¯å¢ƒåŠå¶ç‰‡ç”Ÿç†ç‰¹æ€§çš„å½±å“.

We examined the effects of thinning and reshaping on the canopy micro-domain environment, leaves micro-structure, physiological characteristics and photosynthetic capacity of 16 year-old Fuji apple dense orchards by measuring canopy relative light intensity, temperature, relative humidity, leaf chlorophyll content, micro-structure, and photosynthetic fluorescence. After thinning and reshaping, relative light intensity and temperature of tree canopy were significantly improved, and the distribution was balanced. Effective light intensity (>30%) was 57% higher than that of control (thinning and reshaping, CK), and temperature increased by 1.1 ℃. Due to the improvement of relative light intensity and temperature in the canopy, leaf chlorophyll, leaf thickness, and palisade tissue thickness of thinning trees were increased by 8.7%, 5.4%, and 9.2%, respectively. Net photosynthetic rate, transpiration rate and stomatal conductance of the leaves were also significantly increased, being 12.6%, 17.1% and 7.3% higher than CK, respectively. Leaf photosynthesis capacity of both treatments was limited by non-stomatal factors. After thinning and reshaping, Fm (maximum fluorescence) and qN(non-photochemical quenching coefficient) of PSⅡ in leaves were increased by 1.5% and 2.1%. Leaves did not suffer strong light photoinhibition, with ABS/RC (unit reaction center absorbs light energy), ETo/RC (energy used for electron transfer captured by unit reaction center) and TRo/RC (energy captured by the unit reaction center to reduce QA) of leaves being significantly improved. The physiological characteristics of leaves were closely related to light and temperature environment. After thinning, light and temperature of the orchard canopy were improved, which promoted leaves growth and development, improved foliar micro-structure and photosynthetic efficiency. Thinning and reshaping were suitable strategies for the adjustment and optimization of Fuji orchard density in Loess Plateau of eastern Gansu.

[Effect of thinning and reshaping on the canopy structure and leaf quality at late growth stage in dense apple orchard in Loess Plateau of eastern Gansu, China.] / é—´ä¼æ”¹å½¢å¯¹é™‡ä¸œæ—±å¡¬å¯†é—­è‹¹æžœå›­æ ‘ä½“å† å±‚ç»“æž„å’Œå‘è‚²åŽæœŸå¶ç‰‡è´¨é‡çš„å½±å“.

In order to examine the effects of thinning and reshaping on canopy structure, leaf physio-logical property at late growth stage, characteristic of nutrient accumulation and distribution in leaf, and the spatial and temporal distribution of soil moisture, 18 year-old 'Fuji' apple trees in dense apple orchards were used to measure the canopy size, types and numbers of branches, leaf area index before and after the thinning and reshaping practices. The results showed that before pruning, the photosynthesis was limited by non-stomatal factors, with a reduction in Fv/Fm, Fv/Fo PIabs by 1.2%, 11.5%, 13.9%, respectively. However, the thinning and reshaping practices reduced leaf area index and canopy coverage, increased light interception up to 79% and improved tree construction. The total number of shoots decreased to 1100400 per hectare, while the individual shoot numbers were increased by 5.0% and the ratio of spur increased up to 73%. Due to the improvement of canopy lighting distribution, the average leaf area, specific leaf quality, hundred leaf mass and chlorophyll content were increased. With the increases of photosynthesis, the accumulation of photosynthate such as starch was increased by 143.5%. There was a close correlation between leaf development and light interception. Our results indicated that tree structure and canopy light interception could be improved by thinning and reshaping the dense trees, which resulted in higher leaf growth, development and photosynthetic capability but less water loss. Thinning and reshaping should be recommended to the renewal of the dense apple orchards in Loess Plateau of eastern Gansu.

[Response of distribution pattern and physiological characteristics of apple roots grown in the dry area of eastern Gansu to ground mulching]. / é™‡ä¸œæ—±å¡¬è‹¹æžœæ ¹ç³»åˆ†å¸ƒè§„å¾‹åŠç”Ÿç†ç‰¹æ€§å¯¹åœ°è¡¨è¦†ç›–çš„å“åº”.

The objective of the experiment is to ascertain the effects of different mulching materials on the distribution and physiological activity of apple roots as well as the soil physicochemical pro-perties in the rain-fed Longdong arid areas. With fourteen years old apple trees as test material, the different classes of roots were collected by using soil profile method and stratified sampling in soil profile to investigate the spatial distribution, root biomass, root length and surface area. The activity of root and antioxidant enzymes and some antioxidant indexes were measured. Soil bulk density and soil porosity in different soil layers were determined. The results indicated that ground covering treatment increased the soil moisture, porosity and organic matter content, and the amplification were 2.7%-11.6%, 3.2%-27.7%, 5.1%-36.0%, respectively compared with the control. The soil bulk density was reduced by 88.7%-96.4%. The roots of CK distributed mainly in soil layer of 0-60 cm in depth, 30-120 cm away from the trunk. However, with straw and plastic mulching the roots distributed mainly in the layer of 0-100 cm in depth, 0-150 cm and 0-60 cm away from the trunk, respectively, mostly concentrated in the 20-40 cm layer close to the ground. Plastic mul-ching made a narrower horizontal root distribution than CK and the total fine root amount was 96.4% of that of CK, and that in 0-60 cm layer accounted for 51.6% of the total fine root amount. More-over, the mulching resulted in a higher activity of root and antioxidant enzymes in 0-80 cm layer. The root activity with straw mulching was 111.3%-136.7% as much as the control. For sake of the efficacy on improving root distribution and physiological activity, the straw mulching was suggested as a better way for soil management in apple orchard in dry area of eastern Gansu.