Pleiotropic Effect of GNP1 Underlying Grain Number per Panicle on Sink, Source and Flow in Rice.

Laiyuan Zhai,An Yan,Feng Wang,Jianlong Xu,Shu Wang,Chengwei Liang,Yun Wang

doi:10.3389/fpls.2020.00933

Abstract

Rice yield potential is largely determined by the balance among source capacity, sink strength, and flow fluency. Our previous study indicated that the gene GNP1 encoding gibberellin biosynthesis gene GA20ox1 affects grain number per panicle (GNP) in rice, thus resulting in increase of grain yield. To clarify GNP1 effect on sink, source and flow in regulating rice grain yield, we compared Lemont, a japonica (geng) cultivar, with its near-isogenic line (NIL-GNP1TQ) in Lemont background with introgression of the allele at GNP1 from Teqing, a high-yielding indica (xian) cultivar. NIL-GNP1TQ exhibited averagely 32.8% more GNP than Lemont with the compensation by reduced seed setting rate, panicle number and single-grain weight. However, NIL-GNP1TQ still produced averagely 7.2% higher grain yield than Lemont in two years, mainly attributed to significantly more filled grain number per panicle, and greater vascular system contributing to photoassimilates transport to spikelets. The significantly decreased grain weight of superior spikelets (SS) in NIL-GNP1TQ was ascribed to a significant decrease of grain size while the significantly decreased grain weight of inferior spikelets (IS) ascribed to both grain size and poor grain-filling as compared with Lemont. The low activities of key enzymes of carbon metabolism might account for the poor grain-filling in IS, which resulted in more unfilled grains or small grain bulk density in NIL-GNP1TQ. In addition, low seed setting rate and grain weight of IS in NIL-GNP1TQ might be partially resulted from significantly lower carbohydrate accumulation in culms and leaf sheath before heading compared with Lemont. Our results indicated that significantly increased GNP from introgression of GNP1TQ into Lemont did not highly significantly improve grain yield of NIL-GNP1TQ as expected, due primarily to significant low sink activities in IS and possible insufficient source supply which didn’t fully meet the increased sink capacity. The results provided useful information for improving rice yield potential through reasonably introgressing or pyramiding the favorable alleles underlying source-related or panicle number traits by marker-assisted selection.

Highlights

Rice (Oryza sativa L.), one of the most important cereal crops and a staple food, feeds over 60% of China’s population
The grain number per panicle (GNP) of near-isogenic lines (NIL)-GNP1TQ exhibited averagely 32.8% more than that of Lemont, with much higher (43.5%) number on secondary rachis branches (Table 1)
The NIL-GNP1TQ produced averagely 7.2% higher grain yield than Lemont across the two years. These results suggested that the GNP1TQ is of pleiotropy and has potential value in high yield rice breeding

Summary

Introduction

Rice (Oryza sativa L.), one of the most important cereal crops and a staple food, feeds over 60% of China’s population. Rice breeding experience indicates that good balance of source, sink and translocation capacity (i.e. flow) of assimilates, namely strength sink, strong source and flow fluency is a prerequisite for high yield potential (Peng et al, 2000). Sink is defined as tissues which absorb and utilize photosynthesis, with spikelets being the major primary sink for rice (Li et al, 2018b). Enormous efforts have been made to clarify the physiological mechanism of the relationship among sink size, source capacity and flow transport for improved rice yield potential (Ying et al, 1998; Peng et al, 2000). It is difficult to accurately elucidate the physiological function on relationship of sink size, source capacity and flow fluency in previous comparisons at cultivar level due to the major effect of genetic backgrounds of the examined cultivars

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Results

Discussion

Conclusion