High Temperature-Induced Expression of Rice α-Amylases in Developing Endosperm Produces Chalky Grains
Global warming impairs grain filling in rice and reduces starch accumulation in the endosperm, leading to chalky-appearing grains, which damages their market value. We found previously that high temperature-induced expression of starch-lytic α-amylases during ripening is crucial for grain chalkiness...
Saved in:
Published in | Frontiers in plant science Vol. 8; p. 2089 |
---|---|
Main Authors | , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Switzerland
Frontiers Media S.A
06.12.2017
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | Global warming impairs grain filling in rice and reduces starch accumulation in the endosperm, leading to chalky-appearing grains, which damages their market value. We found previously that high temperature-induced expression of starch-lytic α-amylases during ripening is crucial for grain chalkiness. Because the rice genome carries at least eight functional α-amylase genes, identification of the α-amylase(s) that contribute most strongly to the production of chalky grains could accelerate efficient breeding. To identify α-amylase genes responsible for the production of chalky grains, we characterized the histological expression pattern of eight α-amylase genes and the influences of their overexpression on grain appearance and carbohydrate components through a series of experiments with transgenic rice plants. The promoter activity of most α
amylase genes was elevated to various extents at high temperature. Among them, the expression of
and
was induced in the internal, especially basal to dorsal, region of developing endosperm, whereas that of
was confined near the ventral aleurone. These regions coincided with the site of occurrence of chalkiness, which was in clear contrast to conventionally known expression patterns of the enzyme in the scutellum and aleurone during seed germination. Furthermore, overexpression of α-amylase genes, except for
, in developing endosperm produced various degrees of chalky grains without heat exposure, whereas that of
yielded normal translucent grains, as was the case in the vector control, even though
-overexpressing grains contained enhanced α-amylase activities. The weight of the chalky grains was decreased due to reduced amounts of starch, and microscopic observation of the chalky part of these grains revealed that their endosperm consisted of loosely packed round starch granules that had numerous pits on their surface, confirming the hydrolysis of the starch reserve by α-amylases. Moreover, the chalky grains contained increased amounts of soluble sugars including maltooligosaccharides at the expense of starch. The integrated analyses proposed that expression of
, and
at the specific regions of the developing endosperm could generate the chalkiness. This finding provides the fundamental knowledge to narrow down the targets for the development of high temperature-tolerant premium rice. |
---|---|
Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 This article was submitted to Plant Metabolism and Chemodiversity, a section of the journal Frontiers in Plant Science Edited by: Yasunori Nakamura, Akita Prefectural University, Japan These authors have contributed equally to this work. Reviewed by: Naoko Fujita, Akita Prefectural University, Japan; Chung-An Lu, National Central University, Taiwan Present address: Makoto Hakata, Kyushu Okinawa Agricultural Research Center, National Agriculture and Food Research Organization, Chikugo, Japan |
ISSN: | 1664-462X 1664-462X |
DOI: | 10.3389/fpls.2017.02089 |