A large increase in IAA during development of rice grains correlates with the expression of tryptophan aminotransferase OsTAR1 and a grain‐specific YUCCA

Abstract

The indole-3-acetic acid (IAA) content of developing grains of Oryza sativa subsp. japonica was measured by combined liquid chromatography, tandem mass spectrometry in multiple-reaction-monitoring mode. The increase from 50 ng g(-1) fresh weight to 2.9 µg g(-1) fresh weight from 1 to 14 days after pollination was much larger than that previously reported by enzyme-linked immunoassay methods. The largest increase in IAA content coincided with the start of the major starch deposition phase of grain-fill. The increase in IAA content was strongly correlated with the expression of putative IAA biosynthesis genes, OsYUC9, OsYUC11 and OsTAR1, measured by quantitative reverse transcriptase polymerase chain reaction. These results confirm the importance of the tryptophan aminotransferase/YUCCA pathway in this system. All three genes were expressed in endosperm; expression of OsYUC11 appeared to be confined to endosperm tissue. Phylogenetic analysis indicated that OsYUC11 and AtYUC10 belong to a separate clade of YUCCAs, which do not have orthologues outside the Angiosperms. This clade may have evolved with a specific role in endosperm. Expression of tryptophan decarboxylase in developing rice grains did not correlate with IAA levels, indicating that tryptamine is unlikely to be important for IAA synthesis in this system. In light of these observations, we hypothesize that IAA production in developing rice grains is controlled via expression of OsTAR1, OsYUC9, OsYUC11 and that IAA may be important during starch deposition in addition to its previously suggested role early in grain development.

Heat Stress Is More Damaging to Superior Spikelets than Inferiors of Rice (Oryza sativa L.) due to Their Different Organ Temperatures

“…The greater decrease in kernel weight of superior spikelets than inferiors caused by heat stress might mainly ascribe to the changes in the activity of Q enzymes and IAA concentration, which had been reported to play an important role in mediating the grain-filling in spikelets (Yang et al, 2002; Tao et al, 2003; Abu-Zaitoon et al, 2012). We observed that heat stress significantly decreased the Q enzyme and IAA in the spikelets in both genotypes, but higher reduce were shown in superior spikelet than inferiors.…”

Translating auxin responses into ovules, seeds and yield: Insight from Arabidopsis and the cereals

“…However in monocot species such as maize, Brachypodium and rice, mutations in auxin biosynthetic genes such as TAA1 lead to dramatic developmental defects (Abu‐Zaitoon et al ; Pacheco‐Villalobos et al ; Yoshikawa et al ; Pacheco‐Villalobos et al ). Conversely in monocots, auxin transporter genes, such as PIN1, appear to have more redundant copies than Arabidopsis ; for example, two copies of PIN1 exist in barley, HvPIN1a and HvPIN1b (O'Connor et al ), versus one for Arabidopsis .…”

Contribution of the IAM Pathway to IAA Pool in Developing Rice Grains

“…Additionally, no endogenous IAM was detected from various rice organs including shoots, roots, calli and young fruits (19). Braz Unlike the IAM pathway, the IPA pathway was reported by our research group to have a pivot role in IAA synthesis in rice grains (25). Changes in the expression of OsYUCCA9, OsYUCCA11 as well as OsTAA1were found to significantly correlate with the abrupt and large change in IAA synthesis in the active period of IAA accumulation (between 4 and 7 DAF).…”

“…Braz It has been reported that IAA is produced in high amount in rice kernels compared to vegetative tissue. Abu-Zaitoon, et al (25) showed that IAA levels in kernels increase from undetectable limit at 4 DAF to 2µg/g FW during 14 days from anthesis. The greatest change in auxin synthesis occurs from 4 to 7 DAF.…”

“…The abundance of genetic information derived from microarrays, expressed sequence tags, massively parallel signature sequencing make rice an ideal monocot plant to explore genes involved in the IAM pathway of IAA synthesis. Rice was reported to accumulate large amount of IAA during grain's development (25). The largest increase in IAA was detected between 4 and 7 DAF.…”