Reeger Jenna E, Wheatley Matthew, Yang Yinong, Brown Kathleen M
Intercollege Graduate Degree Program in Plant Biology Huck Institutes of the Life Sciences Penn State University University Park PA USA.
Department of Plant Pathology and Environmental Microbiology Huck Institute of the Life Sciences The Pennsylvania State University University Park PA USA.
Plant Direct. 2021 Jun 15;5(6):e00328. doi: 10.1002/pld3.328. eCollection 2021 Jun.
Root metaxylem vessels are responsible for axial water transport and contribute to hydraulic architecture. Variation in metaxylem vessel size and number can impact drought tolerance in crop plants, including rice, a crop that is particularly sensitive to drought. Identifying and validating candidate genes for metaxylem development would aid breeding efforts for improved varieties for drought tolerance. We identified three transcription factor candidate genes that potentially regulate metaxylem vessel size and number in rice based on orthologous annotations, published expression data, and available root and drought-related QTL data. Single gene knockout mutants were generated for each candidate using CRISPR-Cas9 genome editing. Root metaxylem vessel area and number were analyzed in 6-week-old knockout mutants and wild-type plants under well-watered and drought conditions in the greenhouse. Compared with wild type, () mutants had fewer, smaller metaxylem vessels in shallow roots and more, larger vessels in deep roots in drought conditions, indicating that may be a repressor of drought-induced metaxylem plasticity. The mutants showed fewer but larger metaxylem vessel area in well-watered conditions, but phenotypes were inconsistent under drought treatment. () mutants had fewer, smaller metaxylem vessels in well-watered conditions with greater effects on xylem number than size. mutants had larger shoots and more, deeper roots than the wild type in well-watered conditions, but there were no differences in performance under drought between mutants and wild type. Though these candidate gene mutants did not exhibit large phenotypic effects, the identification and investigation of candidate genes related to metaxylem traits in rice deepen our understanding of metaxylem development and are needed to facilitate incorporation of favorable alleles into breeding populations to improve drought stress tolerance.
根后生木质部导管负责轴向水分运输，并对水力结构有贡献。后生木质部导管大小和数量的变化会影响作物包括水稻（一种对干旱特别敏感的作物）的耐旱性。鉴定和验证后生木质部发育的候选基因将有助于培育耐旱性改良品种的育种工作。基于直系同源注释、已发表的表达数据以及可用的根系和干旱相关QTL数据，我们鉴定了三个可能调控水稻后生木质部导管大小和数量的转录因子候选基因。使用CRISPR-Cas9基因组编辑为每个候选基因生成了单基因敲除突变体。在温室中，对6周龄的敲除突变体和野生型植株在水分充足和干旱条件下的根后生木质部导管面积和数量进行了分析。与野生型相比，（）突变体在干旱条件下浅根中的后生木质部导管更少、更小，而深根中的导管更多、更大，这表明（）可能是干旱诱导的后生木质部可塑性的抑制因子。（）突变体在水分充足条件下后生木质部导管面积更少但更大，但在干旱处理下表现不一致。（）突变体在水分充足条件下后生木质部导管更少、更小，对木质部数量的影响大于大小。（）突变体在水分充足条件下比野生型有更大的地上部分和更多、更深的根系，但突变体和野生型在干旱条件下的表现没有差异。尽管这些候选基因突变体没有表现出大的表型效应，但对水稻中与后生木质部性状相关的候选基因的鉴定和研究加深了我们对后生木质部发育的理解，并且对于将有利等位基因纳入育种群体以提高干旱胁迫耐受性是必要的。
