Biochemical and Biophysical Research Communications
Narrow leaf 1 (NAL1) regulates leaf shape by affecting cell expansion in rice (Oryza sativa L.)
Introduction
Leaf, one of the source tissues, is the main site of photosynthesis in plants, and morphological traits of leaves affect crop yield. Optimal leaf size is an important target in plant breeding programs [1]. The size of leaves is determined by both cell division and cell expansion [2]. To date, several genes that affect leaf size by regulating cell expansion have been isolated in rice. Rice expansin proteins OsEXPA8 and OsEXPB2 play key roles in regulating leaf size by affecting cell expansion [3,4]. Additionally, the proteins encoded by early auxin-inducible genes, such as Gretchen Hagen 3 (GH3) [5], Auxin response factors (ARFs) [6], and Small auxin-up RNAs (SAURs) [7], also regulate leaf size.
The NAL1 gene encodes a putative trypsin-like serine/cysteine protease and plays a key regulatory role in leaf size by affecting polar auxin transport [8] and cell division [9]. Additionally, NAL1 regulates crop yield [10], photosynthesis, source-sink relationship and adventitious root formation in rice [11]. However, despite the importance of NAL1 in a wide variety of plant processes, its mechanism of action remains unclear.
In this study, we performed RNA sequencing (RNA-Seq) analysis on the leaves of 40-day-old wild-type (WT) and nal1 mutant seedlings to understand how NAL1 regulates leaf size. The results revealed that NAL1 regulates leaf size not only by affecting cell division, as reported previously [9], but also by affecting cell expansion, most likely via the long-standing acid growth mechanism. These results advance our understanding of the factors affecting leaf shape and lay a strong foundation for the development of new rice varieties with an optimal leaf shape and high yield.
Section snippets
Plant material and growth conditions
The rice cultivar Zhefu802 was used as the WT in this study. The rice nal1 mutant used in this study has been described previously [8]. All rice plants were grown in environmentally controlled growth chambers at 31 °C day/22 °C night temperature and under a 12 h light/12 h dark photoperiod.
Observation of epidermal and parenchyma cells
The length and width of leaf epidermal cells were measured as previously described [13]. The anatomical investigations of the epidermal cell and culm parenchyma cell were performed as previously described [8
NAL1 regulates leaf shape by controlling cell division and cell expansion
Under our growth conditions, the leaf width and length of nal1 mutant plants were approximately 50% and 69% smaller than those of the WT, respectively (Fig. 1A–C). The difference in leaf width between the WT and nal1 mutant plants was statistically significant at 40 days after germination (data not shown); this was not observed in previous studies [8,9]. Leaf size is affected by both cell division and expansion. Previous study has demonstrated NAL1's effect on controlling cell division [9]. We
Discussion
In rice, mutations in NAL1 cause narrow leaf phenotypes. Previous studies have shown that NAL1 regulates vein patterning and grain yield; however, the mechanism underlying the regulation of leaf growth and development by NAL1 remains unknown. Recently, Jiang and colleagues reported that NAL1 controls leaf width and plant height through its effects on cell division [9]. In the present study, we found that leaf abaxial epidermal cells and culm parenchyma cells in the nal1 mutant were
Acknowledgements
This work was funded by Ministry of Agriculture-Chinese (2016ZX08009003-001-006).
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