Wheat （Triticum aestivum L.） often experiences photoinhibition due to strong light during the grain filling stage. As such, increasing the tolerance of wheat to photoinhibition is very desirable in breeding efforts focused on increasing grain yields. Previous reports have suggested that PROTON GRADIENT REGULATION 5 （PGR5） plays a central role in the generation of a proton gradient across the thylakoid membrane （ApH） and in acclimation to high light intensity conditions. Three PGR5 homoeologues were isolated from wheat, and mapped onto chromosomes 7A, 7B and 7D, respectively. The TaPGR5s shared highly similar genomic sequences and gene structures. The transcripts of TaPGR5s were found to be abundantly expressed in the flag leaves, and were transiently up-regulated by treatment with high light. High light treatment inhibited the net photosynthetic rate （Pn） and the maximal quantum yield ofphotosystem II （Fv/Fm）. Further, these inhibitions were more evident in the leaves with reduced expression of TaPGR5s achieved using virus-induced gene silencing methods. Moreover, reducing TaPGR5 expression impaired the induction of non-photochemical quenching （NPQ）, which caused more severe cell membrane damage and lipid peroxidation in high light. Additionally, we observed that TaPGR5s transcripts were more abundantly expressed in the wheat genotypes with higher ms-delayed light emission （ms-DLE）, a value reflecting transthylakoid ApH. These results suggested that TaPGR5s play important roles in the tolerance of wheat to photoinhibition.
WANG Yuan-geHE XueMA Wen-yingZHAO Xue-qiangLI BinTONG Yi-ping
Plant height is an important agronomic trait. Dramatic increase in wheat yield during the ＂green revolution＂ is mainly due to the widespread utilization of the Reduced height （Rht）-1gene. We analyzed the natural allelic variations of three homoeologous loci Rht-A1, Rht-B1, and Rht-D1 in Chinese wheat （Triticum aestivum L.） micro-core collections and the Rht-B1/D1 genotypes in over 1,500 bred cultivars and germplasms using a modified EcoTILLING. We identified six new Rht-A1 allelic variations （Rht-Alb-g）, eight new Rht-B1 allelic variations （Rht-Blh-o）, and six new Rht-D1 allelic variations （Rht-Dle-j）. These allelic variations contain single nucleotide polymorphisms （SNPs） or small insertions and deletions in the coding or uncoding regions, involving two frame-shift mutations and 15 missenses. Of which, Rht-Dle and Rht-Dlh resulted in the loss of interactions of GID1-DELLA-GID2, Rht-Blicould increase plant height. We found that the Rht-Blh contains the same SNPs and 197 bp fragment insertion as reported in Rht-Blc. Further detection of Rht-Blh in Tibet wheat germplasms and wheat relatives indicated that Rht-Blc may originate from Rht-Blh. These results suggest rich genetic diversity at the Rht-1 loci and provide new resources for wheat breeding.
Ferric-chelate reductase which functions in the reduction of ferric to ferrous iron on root surface is a critical protein for iron ho- meostasis in strategy I plants. LeFROI is a major ferric-chelate reductase involved in iron uptake in tomato. To identify the natural variations of LeFRO1 and to assess their effect on the ferric-chelate reductase activity, we cloned the coding sequences of LeFRO1 from 16 tomato varieties collected from different regions, and detected three types of LeFRO1 （LeFRO1MM, LeFRO1Ailsa and LeFRO1Monita） with five amino acid variations at the positions 21, 24, 112, 195 and 582. Enzyme activity assay revealed that the three types of LeFRO1 possessed different ferric-chelate reductase activity （LeFRO1AiISa 〉 LeFRO1MM 〉 LeFRO1M^nita）. The 112th amino acid residue Ala of LeFRO1 is critical for maintaining the high activity of ferric-chelate reductase, because modification of this amino acid resulted in a significant reduction of enzyme activity. Further, we showed that the combination of the amino acid residue lie at the site 24 with Lys at the site 582 played a positive role in the enzyme activity of LeFRO1. In conclusion, the findings are helpful to understand the natural adaptation mechanisms of plants to iron-limiting stress, and may provide new knowledge to select and manipulate LeFRO1 for improving the iron deficiency tolerance in tomato.
