Abstract
Grain size is an important trait influencing both the yield and quality of rice and its major determinant is glume size. However, how glume size is regulated remains largely unknown. Here, we report the characterization of OsKinesin-13A, which regulates cell elongation and glume length in rice. The mutant of OsKinesin-13A, sar1, displayed length reduction in grains and other organs including internodes, leaves and roots. The grain phenotype in sar1 was directly caused by reduction in glume length, which in turn restricted caryopsis size. Histological results revealed that length decrease in sar1 organs resulted from abnormalities in cell elongation. The orientation of cellulose microfibrils was defective in sar1. Consistently, sar1 showed reduced transverse orientation of cortical microtubules. Further observations demonstrated that microtubule turnover was decreased in sar1. OsKinesin-13A was shown to be an active microtubule depolymerase and mainly distributed on vesicles derived from the Golgi apparatus and destined for the cell surface. Thus, our results suggest that OsKinesin-13A utilizes its microtubule depolymerization activity to promote microtubule turnover, which may not only influence transverse orientation of cortical microtubules but also facilitate vesicle transport from the Golgi apparatus to the cell surface, and thus affects cellulose microfibril orientation and cell elongation.
Highlights
Grain size is an important trait influencing both the yield and quality of rice and its major determinant is glume size
Positional cloning of sar[1] showed that a single nucleotide deletion within the eighth exon of SRS3/OsKINESIN-13A resulted in a premature translation termination from the posterior one-third of the kinesin motor domain (Supplemental Figure 3A–D, Supplemental Table 5)
Our study further revealed that the two main parts of grains, namely glumes and caryopses, were both diminished in length in sar[1], mutation in OsKinesin-13A only directly affected glume elongation and glume length
Summary
Grain size is an important trait influencing both the yield and quality of rice and its major determinant is glume size. Our results suggest that OsKinesin-13A utilizes its microtubule depolymerization activity to promote microtubule turnover, which may influence transverse orientation of cortical microtubules and facilitate vesicle transport from the Golgi apparatus to the cell surface, and affects cellulose microfibril orientation and cell elongation. The biochemical and molecular mechanisms underlying glume cell-size control remain largely unknown, despite several genes, such as SRS3/OsKINESIN-13A, SRS5, PGL1 and APG, having been identified to influence glume cell length[9,10,14]. SRS3/OsKINESIN-13A plays an essential role in cell elongation in glumes as well as other organs such as internodes, leaves and roots and may regulate cell length through influencing the orientation of cortical microtubules and cellulose microfibrils. Our results showed that OsKinesin-13A may promote cell elongation via its microtubule depolymerizing activity that enhances microtubule turnover and facilitates vesicle transport
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