Direct development of plantlets from immature panicles of rice in vitro

An L-type lectin receptor-like kinase promotes starch accumulation during rice pollen maturation

Starch accumulation is key for the maturity of rice pollen grains; however, the regulatory mechanism underlying this process remains unknown. Here, we have isolated a male-sterile rice mutant, abnormal pollen 1 (ap1), which produces nonviable pollen grains with defective starch accumulation. Functional analysis revealed that AP1 encodes an active L-type lectin receptor-like kinase (L-LecRLK). AP1 is localized to the plasma membrane and its transcript is highly accumulated in pollen during the starch synthesis phase. RNA-seq and phosphoproteomic analysis revealed that the expression/phosphorylation levels of numerous genes/proteins involved in starch and sucrose metabolism pathway were significantly altered in the mutant pollen, including a known rice UDP-glucose pyrophosphorylase (OsUGP2). We further found that AP1 physically interacts with OsUGP2 to elevate its enzymatic activity, likely through targeted phosphorylation. These findings revealed a novel role of L-LecRLK in controlling pollen maturity via modulating sucrose and starch metabolism.

Supplementation of 2-Ap, Zn and La Improves 2-Acetyl-1-Pyrroline Concentrations in Detached Aromatic Rice Panicles In Vitro

Aromatic rice is highly prized by consumers worldwide due to its special aromatic character. 2-acetyl-1-pyrroline (2-AP) is considered to be the single most important volatile compound responsible for aroma in aromatic rice. The present study demonstrated the effects of 2-AP, zinc (Zn) and lanthanum (La) on the 2-AP concentration of detached aromatic rice panicles in vitro. Detached panicles from three well-known aromatic cultivars, Guixiangzhan, Pin14, and Pin 15, were cultured separately in basic culture medium supplemented with 2-AP, Zn and La, and 2-AP concentrations were assessed at 7 and 14 days after culture (DAC). The results show that supplementation of 2-AP, Zn and La in the basic culture medium significantly increases the accumulation of proline. 2-AP concentration and the activity of proline dehydrogenase (ProDH) were also increased in rice grains. Zn concentrations were also found to be higher when Zn was added to the basic culture medium, and La concentrations in grains were too low to be measured. Additionally, grain 2-AP concentrations were significantly and positively correlated with proline concentrations, ProDH activities in grains and 2-AP in culture medium. In summary, higher grain 2-AP concentrations might be due to Zn- and La-induced increases in proline concentrations and ProDH activities, as well as the direct uptake and transportation of 2-AP from the culture medium. Furthermore, application of both Zn and La might be helpful for improving aroma formation in rice. However, interactions of both these elements with the complex process of 2-AP formation remain to be explored.

Induction of pollen plantlets in rice by spikelet culture

Induction of pollen callus and subsequent regeneration of plantlets from the callus have been achieved from rice spikelets cultured in a liquid medium containing sucrose, α-naphthalene-acetic acid and kinetin. When spikelets are cultured in a medium containing 6% sucrose, calluses are released into the medium where they continue to increase in size without undergoing organogenesis. On the other hand, in a medium containing 2% sucrose, calluses are retained within the anther locule where they differentiate into plantlets. Cytological studies have shown that calluses have their origin either in the vegetative cell of asymmetrically dividing pollen grains or in both cells of pollen grains which divide more or less equally.